Search

Defects in cilia formation and function result in a range of human skeletal and visceral abnormalities. Mutations in several genes have been identified to cause a proportion of these disorders, some of which display genetic (locus) heterogeneity. Mouse models are valuable for dissecting the function of these genes, as well as for more detailed analysis of the underlying developmental defects. The short-rib polydactyly (SRP) group of disorders are among the most severe human phenotypes caused by cilia dysfunction. We mapped the disease locus from two siblings affected by a severe form of SRP to 2p24, where we identified an in-frame homozygous deletion of exon 5 in WDR35. We subsequently found compound heterozygous missense and nonsense mutations in WDR35 in an independent second case with a similar, severe SRP phenotype. In a mouse mutation screen for developmental phenotypes, we identified a mutation in Wdr35 as the cause of midgestation lethality, with abnormalities characteristic of defects in the Hedgehog signaling pathway. We show that endogenous WDR35 localizes to cilia and centrosomes throughout the developing embryo and that human and mouse fibroblasts lacking the protein fail to produce cilia. Through structural modeling, we show that WDR35 has strong homology to the COPI coatamers involved in vesicular trafficking and that human SRP mutations affect key structural elements in WDR35. Our report expands, and sheds new light on, the pathogenesis of the SRP spectrum of ciliopathies. [ABSTRACT FROM AUTHOR]

Recently, mutations in DJ-1 (PARK7) were described as a novel cause of early-onset parkinsonism. We analysed the DJ-1 gene in a cohort of patients originating from Taiwan with early-onset Parkinson's disease; 41 subjects were clinically and genetically examined. These patients were evaluated previously for the presence of parkin mutations (PARK2) and were found to be negative. The entire DJ-1 open-reading frame was amplified from cDNA, analysed for size alterations indicative of mutations affecting splice motifs, and sequenced to identify coding variants. In addition, we developed quantitative polymerase chain reaction assays to examine the genomic copy number of DJ-1 exons. No potential splice site mutations, coding sequence alterations, or exon deletion/duplications were detected. Our results and previous studies suggest that alterations to DJ-1 are not a common cause of early-onset Parkinson's disease and other causes, genetic and/or environmental, remain to be identified. [ABSTRACT FROM AUTHOR]

Mutations in torsinA, a member of the AAA+ family of ATPases, are associated with early onset-dystonia. A closely related homologue, torsinB, has also been described but the significance of this second form is not clear. Here, we demonstrate that in transfected cells, torsinB has similar electrophoretic mobility to torsinA but is more basic consistent with predictions from the cDNA sequence. Like torsinA, torsinB is glycosylated and localized to PDI-positive structures in cells. However, torsinB unlike torsinA has a tendency to form intracellular inclusions when expressed at similar levels. We were able to confirm previous reports that torsinA is present in brainstem Lewy bodies, but we saw no torsinB-like immunoreactivity in the same structures. These results show that torsins A and B are similar proteins, although there are differences in the abundance of the two homologues and in their recruitment into Lewy bodies. [Copyright &y& Elsevier]

Parkinson's disease (PD) is a common neurodegenerative disorder with clinical features of bradykinesia, rigidity and resting tremor resulting from the deficiency of dopamine in the nigrostriatal system. Recently, PARK6 was identified as a novel locus associated with autosomal recessive PD. Here we report the identification and characterization of a novel human deubiquitylating gene ( USP31 ), which maps to the critical PARK6 region. Database analysis and 5′ RACE identified a 4070 bp cDNA, encoded by 27 exons spanning approximately 105 kbp of genomic sequence. The predicted protein of 1035 amino acids included a conserved ubiquitin hydrolase region (Prosite profile PS50235), a DUSP (domain in ubiquitin specific proteases-Smart00695) and a ubiquitin-like domain (Prosite pattern PS00299). Northern blot analysis revealed a single USP31 transcript of approximately 4 kb, which was primarily expressed in the testis and lung. [ABSTRACT FROM AUTHOR]

Mutations of the parkin gene on chromosome 6q25-27 are the predominant genetic cause of early-onset and autosomal recessive juvenile parkinsonism. Parkin is a multi-domain protein with ubiquitin–protein E3 ligase activity that has a role in the proteasome-mediated degradation of target substrates. Although the parkin gene contains an expanded intron/exon structure and spans more than 1.3 Mb, we have identified a novel transcript that initiates 204 bp upstream of parkin and spans over 0.6 Mb, antisense to parkin. We have tentatively named this novel gene Parkin co-regulated gene, or PACRG. A 35 bp site of bi-directional transcription activation within the common promoter was mapped using dual-luciferase assays. This region appeared to be responsible for the majority of transcription regulation of both genes, and comparison of the mouse and human sequences revealed conserved transcription factor-binding sites. A 15 bp interval within the activation region, containing a non-canonical myc-binding site, bound nuclear protein derived from human substantia nigra. Database analysis identified highly conserved homologs of PACRG encoded by the mouse and Drosophila genomes, and Northern analysis demonstrated that PACRG and parkin were co-expressed in many tissues, including brain, heart and muscle. Western analysis revealed a protein of the predicted size, approximately 30 kDa, which was expressed in mouse and human brain. Although PACRG protein lacks known functional domains, in silico prediction suggests a potential link to the ubiquitin/proteasome system. [Copyright &y& Elsevier]

The Wilson disease (WD) protein (ATP7B) is a copper-transporting P-type ATPase that is responsible for the efflux of hepatic copper into the bile, a process that is essential for copper homeostasis in mammals. Compared with other mammals, sheep have a variant copper phenotype and do not efficiently excrete copper via the bile, often resulting in excessive copper accumulation in the liver. To investigate the function of sheep ATP7B and its potential role in the copper-accumulation phenotype, cDNAs encoding the two forms of ovine ATP7B were transfected into immortalised fibroblast cell lines derived from a Menkes disease patient and a normal control. Both forms of ATP7B were able to correct the copper-retention phenotype of the Menkes cell line, demonstrating each to be functional copper-transporting molecules and suggesting that the accumulation of copper in the sheep liver is not due to a defect in the copper transport function of either form of sATP7B. [Copyright &y& Elsevier]

Parkinson‘s disease (PD) is a common neurodegenerative disorder with clinical features of bradykinesia, rigidity and resting tremor resulting from the deficiency of dopamine in the nigrostriatal system. Previously we mapped a susceptibility gene for an autosomal dominant form of PD to a 10.6 cM region of chromosome 2p (PARK3; OMIM 602404). Here we report the identification and characterization of the human sideroflexin 5 gene (SFXN5), which maps to the critical PARK3 region. Database analysis and 5′-RACE (rapid amplification of cDNA ends) identified a 4191 bp cDNA, encoding a predicted protein of 340 amino acids. The genomic sequence and structure of SFXN5 confirmed the cDNA sequence. Northern blot analysis revealed a single SFXN5 transcript of approximately 4.3 kb, which was primarily expressed in the brain. An examination of SFXN5 expression in specific regions of the human brain revealed high levels of expression in all regions analyzed. Sequence analysis of 2p13 linked individuals affected with PD did not reveal any potentially pathogenic mutations within SFXN5, suggesting SFXN5 does not correspond to PARK3. [Copyright &y& Elsevier]

Objectives: Spinocerebellar ataxia 27B due to GAA repeat expansions in the fibroblast growth factor 14 (FGF14) gene has recently been recognized as a common cause of late‐onset hereditary cerebellar ataxia. Here we present the first report of this disease in the US population, characterizing its clinical manifestations, disease progression, pathological abnormalities, and response to 4‐aminopyridine in a cohort of 102 patients bearing GAA repeat expansions. Methods: We compiled a series of patients with SCA27B, recruited from 5 academic centers across the United States. Clinical manifestations and patient demographics were collected retrospectively from clinical records in an unblinded approach using a standardized form. Post‐mortem analysis was done on 4 brains of patients with genetically confirmed SCA27B. Results: In our cohort of 102 patients with SCA27B, we found that SCA27B was a late‐onset (57 ± 12.5 years) slowly progressive ataxia with an episodic component in 51% of patients. Balance and gait impairment were almost always present at disease onset. The principal finding on post‐mortem examination of 4 brain specimens was loss of Purkinje neurons that was most severe in the vermis most particularly in the anterior vermis. Similar to European populations, a high percent of patients 21/28 (75%) reported a positive treatment response with 4‐aminopyridine. Interpretation: Our study further estimates prevalence and further expands the clinical, imaging and pathological features of SCA27B, while looking at treatment response, disease progression, and survival in patients with this disease. Testing for SCA27B should be considered in all undiagnosed ataxia patients, especially those with episodic onset. ANN NEUROL 2024;96:1092–1103 [ABSTRACT FROM AUTHOR]

The document published in the Journal of Neurology discusses a case study of a 45-year-old male with Cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS). The patient presented with typical clinical features of CANVAS, including cognitive impairment, progressive imbalance, and sensory neuronopathy. Genetic analysis revealed a compound heterozygous copy number variant (CNV) and a pathogenic AAGGG(n) expansion in RFC1, expanding the understanding of the genetic mechanisms underlying CANVAS. The study highlights the importance of sequencing RFC1 in patients with a clinical diagnosis of CANVAS to identify potential genetic causes. [Extracted from the article]

As a result, ddPCR has become a routine research genetic testing method for FCD samples collected from the Epilepsy Surgery Program at the Royal Children's Hospital, Melbourne. Previous studies showed that I MTOR i variants account for ~20-35% of FCD,[2],[[4], [6]] and the five most common I MTOR i variants constitute ~75% of all I MTOR i variants found in FCD (Supplementary Table 1). We read with interest the recent article by Pirozzi I et al. i [1] demonstrating the utility of droplet digital PCR (ddPCR) for the molecular genetic diagnosis of focal malformations of cortical development (FMCD) including focal cortical dysplasia (FCD), hemimegalencephaly (HMEG) and dysplastic megalencephaly (DMEG). This is an effective selection of probes to study DMEG, HMEG and FCD at the same time, resulting in a diagnostic rate of 24.2% for FCD and 81.8% for HMEG/DMEG. [Extracted from the article]

Many drugs on the World Health Organization's list of critical medicines are ototoxic, destroying sensory hair cells within the ear. These drugs preserve life, but patients can experience side effects including permanent hearing loss and vestibular dysfunction. Aminoglycoside ototoxicity was first recognised 80 years ago. However, no preventative treatments have been developed. In order to develop such treatments, we must identify the factors driving hair cell death. In vivo, studies of cell death are typically conducted using mouse models. However, a robust model of aminoglycoside ototoxicity does not exist. Previous studies testing aminoglycoside delivery via intraperitoneal or subcutaneous injection have produced variable ototoxic effects in the mouse. As a result, surgical drug delivery to the rodent ear is often used to achieve ototoxicity. However, this technique does not accurately model clinical practice. In the clinic, aminoglycosides are administered to humans intravenously (i.v.). However, repeated i.v. delivery has not been reported in the mouse. This study evaluated whether repeated i.v. administration of amikacin or tobramycin would induce hearing loss. Daily i.v. injections over a two-week period were well tolerated and transient low frequency hearing loss was observed in the aminoglycoside treatment groups. However, the hearing changes observed did not mimic the high frequency patterns of hearing loss observed in humans. Our results indicate that the i.v. delivery of tobramycin or amikacin is not an effective technique for inducing ototoxicity in mice. This result is consistent with previously published reports indicating that the mouse cochlea is resistant to systemically delivered aminoglycoside ototoxicity. • Daily intravenous injections are well-tolerated by mice over a two week period. • Repeated i.v. injections of amikacin or tobramycin do not induce high frequency hearing loss in mice. • Mice are resistant to amikacin or tobramycin nephrotoxicity. [ABSTRACT FROM AUTHOR]

p38 mitogen-activated protein kinases (P38α and β) and c-Jun N-terminal kinases (JNK1, 2, and 3) are key mediators of the cellular stress response. However, prolonged P38 and JNK signalling is associated with damaging inflammatory responses, reactive oxygen species–induced cell death, and fibrosis in multiple tissues, such as the kidney, liver, central nervous system, and cardiopulmonary systems. These responses are associated with many human diseases, including arthritis, dementia, and multiple organ dysfunctions. Attempts to prevent P38- and JNK-mediated disease using small molecule inhibitors of P38 or JNK have generally been unsuccessful. However, apoptosis signal-regulating kinase 1 (ASK1), an upstream regulator of P38 and JNK, has emerged as an alternative drug target for limiting P38- and JNK-mediated disease. Within this review, we compile the evidence that ASK1 mediates damaging cellular responses via prolonged P38 or JNK activation. We discuss the potential benefits of ASK1 inhibition as a therapeutic and summarise the studies that have tested the effects of ASK1 inhibition in cell and animal disease models, in addition to human clinical trials for a variety of disorders. [ABSTRACT FROM AUTHOR]

Bottom-of-sulcus dysplasia (BOSD) is increasingly recognized as a cause of drug-resistant, surgically-remediable, focal epilepsy, often in seemingly MRI-negative patients. We describe the clinical manifestations, morphological features, localization patterns and genetics of BOSD, with the aims of improving management and understanding pathogenesis. We studied 85 patients with BOSD diagnosed between 2005–2022. Presenting seizure and EEG characteristics, clinical course, genetic findings and treatment response were obtained from medical records. MRI (3 T) and 18F-FDG-PET scans were reviewed systematically for BOSD morphology and metabolism. Histopathological analysis and tissue genetic testing were performed in 64 operated patients. BOSD locations were transposed to common imaging space to study anatomical location, functional network localization and relationship to normal MTOR gene expression. All patients presented with stereotyped focal seizures with rapidly escalating frequency, prompting hospitalization in 48%. Despite 42% patients having seizure remissions, usually with sodium channel blocking medications, most eventually became drug-resistant and underwent surgery (86% seizure-free). Prior developmental delay was uncommon but intellectual, language and executive dysfunction were present in 24%, 48% and 29% when assessed preoperatively, low intellect being associated with greater epilepsy duration. BOSDs were missed on initial MRI in 68%, being ultimately recognized following repeat MRI, 18F-FDG-PET or image postprocessing. MRI features were grey-white junction blurring (100%), cortical thickening (91%), transmantle band (62%), increased cortical T1 signal (46%) and increased subcortical FLAIR signal (26%). BOSD hypometabolism was present on 18F-FDG-PET in 99%. Additional areas of cortical malformation or grey matter heterotopia were present in eight patients. BOSDs predominated in frontal and pericentral cortex and related functional networks, mostly sparing temporal and occipital cortex, and limbic and visual networks. Genetic testing yielded pathogenic mTOR pathway variants in 63% patients, including somatic MTOR variants in 47% operated patients and germline DEPDC5 or NPRL3 variants in 73% patients with familial focal epilepsy. BOSDs tended to occur in regions where the healthy brain normally shows lower MTOR expression, suggesting these regions may be more vulnerable to upregulation of MTOR activity. Consistent with the existing literature, these results highlight (i) clinical features raising suspicion of BOSD; (ii) the role of somatic and germline mTOR pathway variants in patients with sporadic and familial focal epilepsy associated with BOSD; and (iii) the role of 18F-FDG-PET alongside high-field MRI in detecting subtle BOSD. The anatomical and functional distribution of BOSDs likely explain their seizure, EEG and cognitive manifestations and may relate to relative MTOR expression. [ABSTRACT FROM AUTHOR]

This document discusses a study that explores two new repeat expansion disorders for late-onset cerebellar ataxia (CA) that are often accompanied by vestibulopathy and neuropathy. The study compares the severity of bilateral vestibulopathy (BV) in patients with RFC1 repeat expansions and FGF14 repeat expansions. The results show that BV is more severe in RFC1-expansion-positive patients compared to FGF14-expansion-positive patients. The study suggests that the severity of BV may help distinguish RFC1-positive individuals from other ataxic individuals, but further research is needed to investigate these findings due to limitations in the study. [Extracted from the article]

We examined more than 97,000 families from four neurodevelopmental disease cohorts and the UK Biobank to identify phenotypic and genetic patterns in parents contributing to neurodevelopmental disease risk in children. We identified within- and cross-disorder correlations between six phenotypes in parents and children, such as obsessive-compulsive disorder (R = 0.32–0.38, p < 10−126). We also found that measures of sub-clinical autism features in parents are associated with several autism severity measures in children, including biparental mean Social Responsiveness Scale scores and proband Repetitive Behaviors Scale scores (regression coefficient = 0.14, p = 3.38 × 10−4). We further describe patterns of phenotypic similarity between spouses, where spouses show correlations for six neurological and psychiatric phenotypes, including a within-disorder correlation for depression (R = 0.24–0.68, p < 0.001) and a cross-disorder correlation between anxiety and bipolar disorder (R = 0.09–0.22, p < 10−92). Using a simulated population, we also found that assortative mating can lead to increases in disease liability over generations and the appearance of "genetic anticipation" in families carrying rare variants. We identified several families in a neurodevelopmental disease cohort where the proband inherited multiple rare variants in disease-associated genes from each of their affected parents. We further identified parental relatedness as a risk factor for neurodevelopmental disorders through its inverse relationship with variant pathogenicity and propose that parental relatedness modulates disease risk by increasing genome-wide homozygosity in children (R = 0.05–0.26, p < 0.05). Our results highlight the utility of assessing parent phenotypes and genotypes toward predicting features in children who carry rare variably expressive variants and implicate assortative mating as a risk factor for increased disease severity in these families. [Display omitted] Many rare genetic variants are variably expressive, conferring risk for a range of clinical features with incomplete penetrance. We implicate assortative mating as a risk factor for disease in families carrying these variants by increasing genetic disease liability over generations, leading to the "genetic anticipation" observed in these families. [ABSTRACT FROM AUTHOR]

Objective: Friedreich ataxia (FRDA) is an inherited neurodegenerative disease characterized by ataxia and cardiomyopathy. Homozygous GAA trinucleotide repeat expansions in the first intron of FXN occur in 96% of affected individuals and reduce frataxin expression. Remaining individuals are compound heterozygous for a GAA expansion and a FXN point/insertion/deletion mutation. We examined disease-causing mutations and the impact on frataxin structure/function and clinical outcome in FRDA.Methods: We compared clinical information from 111 compound heterozygotes and 131 individuals with homozygous expansions. Frataxin mutations were examined using structural modeling, stability analyses and systematic literature review, and categorized into four groups: (1) homozygous expansions, and three compound heterozygote groups; (2) null (no frataxin produced); (3) moderate/strong impact; and (4) minimal impact. Mean age of onset and the presence of cardiomyopathy and diabetes mellitus were compared using regression analyses.Results: Mutations in the hydrophobic core of frataxin affected stability whereas surface residue mutations affected interactions with iron sulfur cluster assembly and heme biosynthetic proteins. The null group of compound heterozygotes had significantly earlier age of onset and increased diabetes mellitus, compared to the homozygous expansion group. There were no significant differences in mean age of onset between homozygotes and the minimal and moderate/strong impact groups.Interpretation: In compound heterozygotes, expression of partially functional mutant frataxin delays age of onset and reduces diabetes mellitus, compared to those with no frataxin expression from the non-expanded allele. This integrated analysis of categorized frataxin mutations and their correlation with clinical outcome provide a definitive resource for investigating disease pathogenesis in FRDA. [ABSTRACT FROM AUTHOR]

Objective: Favorable seizure outcome is reported following resection of bottom‐of‐sulcus dysplasia (BOSD). We assessed the distribution of epileptogenicity and dysplasia in and around BOSD to better understand this clinical outcome and the optimal surgical approach. Methods: We studied 27 children and adolescents with magnetic resonance imaging (MRI)‐positive BOSD who underwent epilepsy surgery; 85% became seizure‐free postresection (median = 5.0 years follow‐up). All patients had resection of the dysplastic sulcus, and 11 had additional resection of the gyral crown (GC) or adjacent gyri (AG). Markers of epileptogenicity were relative cortical hypometabolism on preoperative 18F‐fluorodeoxyglucose (FDG) positron emission tomography (PET), and spiking, ripples, fast ripples, spike–high‐frequency oscillation cross‐rate, and phase amplitude coupling (PAC) on preresection and postresection electrocorticography (ECoG), all analyzed at the bottom‐of‐sulcus (BOS), top‐of‐sulcus (TOS), GC, and AG. Markers of dysplasia were increased cortical thickness on preoperative MRI, and dysmorphic neuron density and variant allele frequency of somatic MTOR mutations in resected tissue, analyzed at similar locations. Results: Relative cortical metabolism was significantly reduced and ECoG markers were significantly increased at the BOS compared to other regions. Apart from spiking and PAC, which were greater at the TOS compared to the GC, there were no significant differences in PET and other ECoG markers between the TOS, GC, and AG, suggesting a cutoff of epileptogenicity at the TOS rather than a tapering gradient on the cortical surface. MRI and tissue markers of dysplasia were all maximal in the BOS, reduced in the TOS, and mostly absent in the GC. Spiking and PAC reduced significantly over the GC after resection of the dysplastic sulcus. Significance: These findings support the concept that dysplasia and intrinsic epileptogenicity are mostly limited to the dysplastic sulcus in BOSD and support resection or ablation confined to the MRI‐visible lesion as a first‐line surgical approach. 18F‐FDG PET and ECoG abnormalities in surrounding cortex seem to be secondary phenomena. [ABSTRACT FROM AUTHOR]

Reelin, a large extracellular protein, plays several critical roles in brain development and function. It is encoded by RELN , first identified as the gene disrupted in the reeler mouse, a classic neurological mutant exhibiting ataxia, tremors and a 'reeling' gait. In humans, biallelic variants in RELN have been associated with a recessive lissencephaly variant with cerebellar hypoplasia, which matches well with the homozygous mouse mutant that has abnormal cortical structure, small hippocampi and severe cerebellar hypoplasia. Despite the large size of the gene, only 11 individuals with RELN -related lissencephaly with cerebellar hypoplasia from six families have previously been reported. Heterozygous carriers in these families were briefly reported as unaffected, although putative loss-of-function variants are practically absent in the population (probability of loss of function intolerance = 1). Here we present data on seven individuals from four families with biallelic and 13 individuals from seven families with monoallelic (heterozygous) variants of RELN and frontotemporal or temporal-predominant lissencephaly variant. Some individuals with monoallelic variants have moderate frontotemporal lissencephaly, but with normal cerebellar structure and intellectual disability with severe behavioural dysfunction. However, one adult had abnormal MRI with normal intelligence and neurological profile. Thorough literature analysis supports a causal role for monoallelic RELN variants in four seemingly distinct phenotypes including frontotemporal lissencephaly, epilepsy, autism and probably schizophrenia. Notably, we observed a significantly higher proportion of loss-of-function variants in the biallelic compared to the monoallelic cohort, where the variant spectrum included missense and splice-site variants. We assessed the impact of two canonical splice-site variants observed as biallelic or monoallelic variants in individuals with moderately affected or normal cerebellum and demonstrated exon skipping causing in-frame loss of 46 or 52 amino acids in the central RELN domain. Previously reported functional studies demonstrated severe reduction in overall RELN secretion caused by heterozygous missense variants p.Cys539Arg and p.Arg3207Cys associated with lissencephaly suggesting a dominant-negative effect. We conclude that biallelic variants resulting in complete absence of RELN expression are associated with a consistent and severe phenotype that includes cerebellar hypoplasia. However, reduced expression of RELN remains sufficient to maintain nearly normal cerebellar structure. Monoallelic variants are associated with incomplete penetrance and variable expressivity even within the same family and may have dominant-negative effects. Reduced RELN secretion in heterozygous individuals affects only cortical structure whereas the cerebellum remains intact. Our data expand the spectrum of RELN -related neurodevelopmental disorders ranging from lethal brain malformations to adult phenotypes with normal brain imaging. [ABSTRACT FROM AUTHOR]

Mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE) is an important cause of drug-resistant epilepsy. A significant subset of individuals diagnosed with MOGHE display somatic mosaicism for loss-of-function variants in SLC35A2 , which encodes the UDP-galactose transporter. We developed a mouse model to investigate how disruption of this transporter leads to a malformation of cortical development. We used in utero electroporation and CRISPR/Cas9 to knockout Slc35a2 in a subset of layer 2/3 cortical neuronal progenitors in the developing brains of male and female fetal mice to model mosaic expression. Mosaic Slc35a2 knockout was verified through next-generation sequencing and immunohistochemistry of GFP-labelled transfected cells. Histology of brain tissue in mosaic Slc35a2 knockout mice revealed the presence of upper layer-derived cortical neurons in the white matter. Reconstruction of single filled neurons identified altered dendritic arborisation with Slc35a2 knockout neurons having increased complexity. Whole-cell electrophysiological recordings revealed that Slc35a2 knockout neurons display reduced action potential firing, increased afterhyperpolarisation duration and reduced burst-firing when compared with control neurons. Mosaic Slc35a2 knockout mice also exhibited significantly increased epileptiform spiking and increased locomotor activity. We successfully generated a mouse model of mosaic Slc35a2 deficiency, which recapitulates features of the human phenotype, including impaired neuronal migration. We show that knockout in layer 2/3 cortical neuron progenitors is sufficient to disrupt neuronal excitability, increase epileptiform activity and cause hyperactivity in mosaic mice. Our mouse model provides an opportunity to further investigate the disease mechanisms that contribute to MOGHE and facilitate the development of precision therapies. • A mouse model of MOGHE was generated by cortical mosaic Slc35a2 knockout. • Slc35a2 mosaicism causes increased network-level epileptiform activity. • Excitatory neuron dendritic arborisation is altered by Slc35a2 knockout. • Electrophysiological recordings from knockout neurons reveal decreased excitability. [ABSTRACT FROM AUTHOR]

Abstract: PArkin Co-Regulated Gene is a gene that shares a bidirectional promoter with the Parkinson''s disease associated gene parkin. The encoded protein (PACRG) is found in Lewy bodies and glial cytoplasmic inclusions, the pathological hallmarks of parkinsonian disorders. To investigate the function and regulation of PACRG, cells were treated with the proteasomal inhibitor, MG-132. As previously reported with parkin, inhibition of the proteasome resulted in the formation of aggresomes that contained endogenous PACRG. Increased levels of exogenous PACRG resulted in an increase in aggresome formation, and conferred significant resistance to aggresome disruption and cell death mediated by microtubule depolymerisation. In contrast, shRNA mediated knockdown of PACRG significantly reduced aggresome numbers. Elevated levels of PACRG also resulted in increased autophagy, as demonstrated by biochemical and quantitative analysis of autophagic vesicles, whereas lowered levels of PACRG resulted in reduced autophagy. These results suggest a role for PACRG in aggresome formation and establish a further link between the UPS and autophagy. [Copyright &y& Elsevier]

Abstract: Mutation of the parkin gene (parkin) is the most common cause of early-onset Parkinson’s disease and to date over 100 different mutations have been described. However, screening of parkin is complicated by its genomic architecture and context. Notably, dosage alterations in parkin account for greater than 50% of mutations detected in some cohort studies. To improve the accuracy and reproducibility of parkin genomic dosage assays we have identified and analysed cell lines with chromosomal abnormalities affecting 6q26. FISH and real-time PCR analysis identified cell lines with reduced or increased copy number spanning the entire parkin locus. These cell lines represent a valuable resource to facilitate accurate copy number determination of any parkin exon. The reagents are easily obtainable and are compatible with current quantitative technologies and platforms. [Copyright &y& Elsevier]

Aminoglycoside antibiotics are lifesaving medicines, crucial for the treatment of chronic or drug resistant infections. However, aminoglycosides are toxic to the sensory hair cells in the inner ear. As a result, aminoglycoside-treated individuals can develop permanent hearing loss and vestibular impairment. There is considerable evidence that reactive oxygen species (ROS) production and the subsequent phosphorylation of c-Jun N-terminal kinase (JNK) and P38 mitogen-activated protein kinase (P38) drives apoptosis in aminoglycoside-treated hair cells. However, treatment strategies that directly inhibit ROS, JNK, or P38 are limited by the importance of these molecules for normal cellular function. Alternatively, the upstream regulator apoptosis signal-regulating kinase 1 (ASK1/MAP3K5) is a key mediator of ROS-induced JNK and P38 activation under pathologic but not homeostatic conditions. We investigated ASK1 as a mediator of drug-induced hair cell death using cochlear explants from Ask1 knockout mice, demonstrating that Ask1 deficiency attenuates neomycin-induced hair cell death. We then evaluated pharmacological inhibition of ASK1 with GS-444217 as a potential otoprotective therapy. GS-444217 significantly attenuated hair cell death in neomycin-treated explants but did not impact aminoglycoside efficacy against P. aeruginosa in the broth dilution test. Overall, we provide significant pre-clinical evidence that ASK1 inhibition represents a novel strategy for preventing aminoglycoside ototoxicity. Key messages: ASK1 is an upstream, redox-sensitive regulator of P38 and JNK, which are known mediators of hair cell death. Ask1 knockout does not affect hair cell development in vivo, but significantly reduces aminoglycoside-induced hair cell death in vitro. A small-molecule inhibitor of ASK1 attenuates neomycin-induced hair cell death, and does not impact antibiotic efficacy in vitro. ASK1 may be a novel molecular target for preventing aminoglycoside-induced hearing loss. [ABSTRACT FROM AUTHOR]

Spinocerebellar ataxia type 2 (SCA2) has been recognized recently as an uncommon cause of parkinsonism, an alternate presentation to the typical cerebellar disorder. This research review summarizes the existing literature on parkinsonism-predominant presentation SCA2 and presents new clinical cases of patients with this condition. Various phenotypes are noted in this subtype of SCA2, including parkinsonism indistinguishable from idiopathic Parkinson's disease (PD), parkinsonism plus ataxia, motor neuron disease, and postural tremor. In several kindreds with multiple affected family members, the SCA2 expansion segregated with disease; in addition, several single cases of parkinsonism with and without a family history are also described. The number of repeats in symptomatic patients ranged from 33 to 43. Interruption of the CAG repeat with CAA, CGG, or CCG was found in some individuals, possibly stabilizing the repeat structure and accounting for the relative stability of the repeat size across generations in some families; allele length is not necessarily indicative of trinucleotide repeat architecture. Positron emission tomography scanning in one family showed reduced fluorodopa uptake and normal to increased raclopride binding with a rostrocaudal gradient similar to that found in idiopathic PD. This review emphasizes the importance of testing for SCA2 in patients with parkinsonism and a family history of neurodegenerative disorders. Testing for SCA2 is also important in studies of inherited parkinsonism. © 2004 Movement Disorder Society [ABSTRACT FROM AUTHOR]

One hypothesis for the etiology of Parkinson''s disease (PD) is that subsets of neurons are vulnerable to a failure in proteasome-mediated protein turnover. Here we show that overexpression of mutant α-synuclein increases sensitivity to proteasome inhibitors by decreasing proteasome function. Overexpression of parkin decreases sensitivity to proteasome inhibitors in a manner dependent on parkin''s ubiquitin-protein E3 ligase activity, and antisense knockdown of parkin increases sensitivity to proteasome inhibitors. Mutant α-synuclein also causes selective toxicity to catecholaminergic neurons in primary midbrain cultures, an effect that can be mimicked by the application of proteasome inhibitors. Parkin is capable of rescuing the toxic effects of mutant α-synuclein or proteasome inhibition in these cells. Therefore, parkin and α-synuclein are linked by common effects on a pathway associated with selective cell death in catecholaminergic neurons. [Copyright &y& Elsevier]

Parkinson's disease (PD) is a common neurodegenerative disorder with clinical features of bradykinesia, rigidity, resting tremor and postural instability resulting from the deficiency of dopamine in the nigrostriatal system. Previously we mapped a susceptibility gene for an autosomal dominant form of PD to a 10.6 cM region of chromosome 2p (PARK3; OMIM 602404). A common haplotype shared by two North American kindreds (Families B and C) genealogically traced to Southern Denmark and Northern Germany suggested a founder effect. Here we report progress in the refinement of the PARK3 locus and sequence analysis of candidate genes within the region. Members of families B and C were genotyped using polymorphic markers, reducing the minimum common haplotype to eight markers spanning a physical distance of 2.5 Mb. Analysis of 14 genes within the region did not reveal any potentially pathogenic mutations segregating with the disease, implying that none of these genes are likely candidates for PARK3. [ABSTRACT FROM AUTHOR]

Focal cortical dysplasia (FCD) and hemimegalencephaly (HME) are related malformations with shared etiologies. We report three patients with a spectrum of cortical malformations associated with pathogenic brain‐specific somatic Ras homolog enriched in brain (RHEB) variants. The somatic variant load directly correlated with the size of the malformation, with upregulated mTOR activity confirmed in dysplastic tissues. Laser capture microdissection showed enrichment of RHEB variants in dysmorphic neurons and balloon cells. Our findings support the role of RHEB in a spectrum of cortical malformations confirming that FCD and HME represent a disease continuum, with the extent of dysplastic brain directly correlated with the somatic variant load. [ABSTRACT FROM AUTHOR]

Chudley-McCullough syndrome, a rare autosomal recessive disorder due to pathogenic variants in the GPSM2 (G-protein signaling modulator 2) gene, is characterized by early-onset sensorineural deafness and a typical combination of brain malformations, including ventriculomegaly, (partial) agenesis of the corpus callosum, cerebellar dysplasia, arachnoid cysts, frontal subcortical heterotopia, and midline polymicrogyria. When hearing loss is managed early, most patients have minor or no impairment of motor and cognitive development, despite the presence of brain malformations. We report 2 cases of Chudley-McCullough syndrome, one presenting with congenital deafness and normal development except for speech delay and one presenting prenatally with ventriculomegaly and an atypical postnatal course characterized by epileptic spasms, deafness, and moderate intellectual disability. These highlight the challenges faced by clinicians when predicting prognosis based on pre- or postnatal imaging of brain malformations. We have also reviewed the phenotype and genotype of previous published cases to better understand Chudley-McCullough syndrome. [ABSTRACT FROM AUTHOR]

Background: Spinocerebellar ataxias are often caused by expansions of short tandem repeats. Recent methodological advances have made repeat expansion (RE) detection with whole-genome sequencing (WGS) feasible.Objectives: The objective of this study was to determine the genetic basis of ataxia in a multigenerational Australian pedigree with autosomal-dominant inheritance.Methods and Results: WGS was performed on 3 affected relatives. The sequence data were screened for known pathogenic REs using 2 RE detection tools: exSTRa and ExpansionHunter. This screen provided a clear and rapid diagnosis (<5 days from receiving the sequencing data) of spinocerebellar ataxia 36, a rare form of ataxia caused by an intronic GGCCTG RE in NOP56.Conclusions: The diagnosis of rare ataxias caused by REs is highly feasible and cost-effective with WGS. We propose that WGS could potentially be implemented as the frontline, cost-effective methodology for the molecular testing of individuals with a clinical diagnosis of ataxia. © 2020 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Purpose: The complexity and severity of rare genetic conditions pose substantial burden to families. While the importance of spillovers on carers' health in resource allocation decisions is increasingly recognised, there is significant lack of empirical evidence in the context of rare diseases. The objective of this study was to estimate the health spillovers of paediatric rare genetic conditions on parents. Methods: Health-related quality-of-life (HRQoL) data from children with rare genetic conditions (genetic kidney diseases, mitochondrial diseases, epileptic encephalopathies, brain malformations) and their parents were collected using the CHU9D and SF-12 measures, respectively. We used two approaches to estimate parental health spillovers. To quantify the 'absolute health spillover', we matched our parent cohort to the Australian general population. To quantify the 'relative health spillover', regression models were applied using the cohort data. Results: Parents of affected children had significantly lower HRQoL compared to matched parents in the general public (− 0.06; 95% CIs − 0.08, − 0.04). Multivariable regression demonstrated a positive association between parental and child health. The mean magnitude of HRQoL loss in parents was estimated to be 33% of the HRQoL loss observed in children (95% CIs 21%, 46%). Conclusion: Paediatric rare genetic conditions appear to be associated with substantial parental health spillovers. This highlights the importance of including health effects on family members and caregivers into economic evaluation of genomic technologies and personalised medicine. Overlooking spillover effects may undervalue the benefits of diagnosis and management in this context. This study also expands the knowledge of family spillover to the rare disease spectrum. [ABSTRACT FROM AUTHOR]

Pathogenic variants in the gene encoding deleted in colorectal cancer (DCC) are the first genetic cause of isolated agenesis of the corpus callosum (ACC). Here we present the detailed neurological, brain magnetic resonance imaging (MRI), and neuropsychological characteristics of 12 individuals from three families with pathogenic variants in DCC (aged 8-50y), who showed ACC and mirror movements (n=5), mirror movements only (n=2), ACC only (n=3), or neither ACC nor mirror movements (n=2). There was heterogeneity in the neurological and neuroimaging features on brain MRI, and performance across neuropsychological domains ranged from extremely low (impaired) to within normal limits (average). Our findings show that ACC and/or mirror movements are associated with low functioning in select neuropsychological domains and a DCC pathogenic variant alone is not sufficient to explain the disability. WHAT THIS PAPER ADDS: Neuropsychological impairment severity is related to presence of mirror movements and/or agenesis of the corpus callosum. A DCC pathogenic variant in isolation is associated with the best prognosis. [ABSTRACT FROM AUTHOR]

Background: Pathogenic variants in the small GTPase Ras Analogue in Brain 39b (RAB39B) have been linked to the development of early-onset parkinsonism. The study was aimed at delineating the clinical and neuropathological features associated with a previously reported pathogenic variant in RAB39B (c.503C>A p.T168K) and testing for dysregulation of RAB39B in idiopathic PD.Methods: Clinical details of a male individual hemizygous for the T168K variant were collected by systematic review of medical records. Neuropathological studies of fixed brain tissue were performed and steady-state RAB39B levels were determined by western blot analysis.Results: Neuropathological examination showed extensive dopaminergic neuron loss, widespread Lewy pathology, and iron accumulation in the substantia nigra. Additional pathology was observed in the hippocampus and thalamus. Western blot analysis demonstrated that the T168K variant results in loss of RAB39B. In individuals with idiopathic PD (n = 10, 6 male/4 female), steady-state RAB39B was significantly reduced in the prefrontal cortex and substantia nigra.Conclusions: T168K RAB39B is unstable in vivo and associated with dopaminergic neuron loss and Lewy pathology. Dysregulation of RAB39B in the prefrontal cortex and substantia nigra of individuals with idiopathic PD potentially implicates the protein more broadly in the pathological mechanisms underlying PD and related Lewy body disorders. © 2020 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Background: Pathogenic variants in the small GTPase Ras Analogue in Brain 39b (RAB39B) have been linked to the development of early‐onset parkinsonism. The study was aimed at delineating the clinical and neuropathological features associated with a previously reported pathogenic variant in RAB39B (c.503C>A p.T168K) and testing for dysregulation of RAB39B in idiopathic PD. Methods: Clinical details of a male individual hemizygous for the T168K variant were collected by systematic review of medical records. Neuropathological studies of fixed brain tissue were performed and steady‐state RAB39B levels were determined by western blot analysis. Results: Neuropathological examination showed extensive dopaminergic neuron loss, widespread Lewy pathology, and iron accumulation in the substantia nigra. Additional pathology was observed in the hippocampus and thalamus. Western blot analysis demonstrated that the T168K variant results in loss of RAB39B. In individuals with idiopathic PD (n = 10, 6 male/4 female), steady‐state RAB39B was significantly reduced in the prefrontal cortex and substantia nigra. Conclusions: T168K RAB39B is unstable in vivo and associated with dopaminergic neuron loss and Lewy pathology. Dysregulation of RAB39B in the prefrontal cortex and substantia nigra of individuals with idiopathic PD potentially implicates the protein more broadly in the pathological mechanisms underlying PD and related Lewy body disorders. © 2020 International Parkinson and Movement Disorder Society [ABSTRACT FROM AUTHOR]

Pathogenic variants in the gene encoding the small GTPase Ras analogue in Brain 39b (RAB39B) are associated with early-onset parkinsonism. In this study we investigated the expression and localization of RAB39B (RNA and protein) in mouse brain tissue to gain a better understanding of its normal physiological function(s) and role in disease. We developed novel resources, including monoclonal antibodies directed against RAB39B and mice with Rab39b knockout, and performed real-time PCR and western blot analysis on whole brain lysates. To determine the spatial localization of Rab39b RNA and protein, we performed in-situ hybridization and immunohistochemistry on fresh frozen and fixed brain tissue. Our results show that RAB39B is localized throughout the cortex, hippocampus and substantia nigra of mice throughout postnatal life. We found high levels of RAB39B within MAP2 positive cortical and hippocampal neurons, and TH positive dopaminergic neurons in the substantia nigra pars compacta. Our studies support and extend current knowledge of the localization of RAB39B. We validate RAB39B as a neuron-enriched protein and demonstrate that it is present throughout the mouse cortex and hippocampus. Further, we observe high levels in the substantia nigra pars compacta, the brain region most affected in Parkinson's disease pathology. The distribution of Rab39b is consistent with human disease associations with parkinsonism and cognitive impairment. We also describe and validate novel resources, including monoclonal antibodies directed against RAB39B and mice with Rab39b knockout, both of which are valuable tools for future studies of the molecular function of RAB39B. [ABSTRACT FROM AUTHOR]

The Mendelian disorders of chromatin machinery (MDCMs) represent a distinct subgroup of disorders that present with neurodevelopmental disability. The chromatin machinery regulates gene expression by a range of mechanisms, including by post-translational modification of histones, responding to histone marks, and remodelling nucleosomes. Some of the MDCMs that impact on histone modification may have potential therapeutic interventions. Two potential treatment strategies are to enhance the intracellular pool of metabolites that can act as substrates for histone modifiers and the use of medications that may inhibit or promote the modification of histone residues to influence gene expression. In this article we discuss the influence and potential treatments of histone modifications involving histone acetylation and histone methylation. Genomic technologies are facilitating earlier diagnosis of many Mendelian disorders, providing potential opportunities for early treatment from infancy. This has parallels with how inborn errors of metabolism have been afforded early treatment with newborn screening. Before this promise can be fulfilled, we require greater understanding of the biochemical fingerprint of these conditions, which may provide opportunities to supplement metabolites that can act as substrates for chromatin modifying enzymes. Importantly, understanding the metabolomic profile of affected individuals may also provide disorder-specific biomarkers that will be critical for demonstrating efficacy of treatment, as treatment response may not be able to be accurately assessed by clinical measures. [ABSTRACT FROM AUTHOR]

Background: Intraoperative awareness with recall while under apparently adequate general anesthesia is a rare, unexplained, and often very distressing phenomenon. It is possible that a relatively small number of genetic variants might underlie the failure of general anesthetic drugs to adequately suppress explicit memory formation and recall in the presence of apparently adequate anesthesia concentrations.Methods: The authors recruited 12 adult patients who had experienced an episode of intraoperative awareness with recall (compared with 12 controls), performed whole exome sequencing, and applied filtering to obtain a set of genetic variants that might be associated with intraoperative awareness with recall. The criteria were that the variant (1) had a minor allele frequency less than 0.1% in population databases, (2) was within exonic or splicing regions, (3) caused a nonsynonymous change, (4) was predicted to be functionally damaging, (5) was expressed in the top 50% of genes expressed in the brain, and (6) was within genes in Kyoto Encyclopedia of Genes and Genomes pathways associated with general anesthesia, drug metabolism, arousal, and memory.Results: The authors identified 29 rare genetic variants in 27 genes that were absent in controls and could plausibly be associated with this disorder. One variant in CACNA1A was identified in two patients and two different variants were identified in both CACNA1A and CACNA1S. Of interest was the relative overrepresentation of variants in genes encoding calcium channels and purinergic receptors.Conclusions: Within the constraints of the filtering process used, the authors did not find any single gene variant or gene that was strongly associated with intraoperative awareness with recall. The authors report 27 candidate genes and associated pathways identified in this pilot project as targets of interest for future larger biologic and epidemiologic studies. [ABSTRACT FROM AUTHOR]

Focal cortical dysplasia (FCD) causes drug‐resistant epilepsy and is associated with pathogenic variants in mTOR pathway genes. How germline variants cause these focal lesions is unclear, however a germline + somatic "2‐hit" model is hypothesized. In a boy with drug‐resistant epilepsy, FCD, and a germline DEPDC5 pathogenic variant, we show that a second‐hit DEPDC5 variant is limited to dysmorphic neurons, and the somatic mutation load correlates with both dysmorphic neuron density and the epileptogenic zone. These findings provide new insights into the molecular and cellular correlates of FCD determining drug‐resistant epilepsy and refine conceptualization of the epileptogenic zone. [ABSTRACT FROM AUTHOR]

Background: Bi-allelic mutations in PARK7 are a rare cause of autosomal recessive early onset Parkinson's disease (EO-PD). To date, 30 individuals harbouring 20 unique causative variants have been described. Understanding of the spectrum of clinical features and natural history of PARK7 mediated EO-PD remain limited.Methods: We studied a family with three offspring, two of whom were affected with EO-PD. Family members underwent detailed clinical examination and DNA samples from both affected individuals and parents were analysed by exome sequencing.Results: Two brothers of Iranian descent presented at age 29 years with Parkinsonism associated with high-pitched voice and hypomimia. The brothers were followed over a six and fifteen-year period and displayed typical levodopa responsive slowly-progressive Parkinsonism. A novel homozygous frameshift mutation in PARK7 [NM_007262.4:c.90dupG, p(Ile31Aspfs*2)] was identified.Conclusions: Here we report the clinical presentation and progression of EO-PD in brothers with a novel pathogenic PARK7 variant. We expand the clinical phenotype and provide an update of clinical and pathological features of the disorder. [ABSTRACT FROM AUTHOR]

Repeat expansions cause more than 30 inherited disorders, predominantly neurogenetic. These can present with overlapping clinical phenotypes, making molecular diagnosis challenging. Single-gene or small-panel PCR-based methods can help to identify the precise genetic cause, but they can be slow and costly and often yield no result. Researchers are increasingly performing genomic analysis via whole-exome and whole-genome sequencing (WES and WGS) to diagnose genetic disorders. However, until recently, analysis protocols could not identify repeat expansions in these datasets. We developed exSTRa (expanded short tandem repeat algorithm), a method that uses either WES or WGS to identify repeat expansions. Performance of exSTRa was assessed in a simulation study. In addition, four retrospective cohorts of individuals with eleven different known repeat-expansion disorders were analyzed with exSTRa. We assessed results by comparing the findings to known disease status. Performance was also compared to three other analysis methods (ExpansionHunter, STRetch, and TREDPARSE), which were developed specifically for WGS data. Expansions in the assessed STR loci were successfully identified in WES and WGS datasets by all four methods with high specificity and sensitivity. Overall, exSTRa demonstrated more robust and superior performance for WES data than did the other three methods. We demonstrate that exSTRa can be effectively utilized as a screening tool for detecting repeat expansions in WES and WGS data, although the best performance would be produced by consensus calling, wherein at least two out of the four currently available screening methods call an expansion. [ABSTRACT FROM AUTHOR]

Mutations in DEPDC5 and NPRL3 subunits of GATOR1, a modulator of mechanistic target of rapamycin (mTOR), are linked to malformations of cortical development (MCD). Brain specimens from these individuals reveal abnormal cortical lamination, altered cell morphology, and hyperphosphorylation of ribosomal S6 protein (PS6), a marker for mTOR activation. While numerous studies have examined GATOR1 subunit function in non-neuronal cell lines, few have directly assessed loss of GATOR1 subunit function in neuronal cell types. We hypothesized that DEPDC5 or NPRL3 shRNA-mediated knockdown ( DEPDC5/NPRL3 KD) leads to inappropriate functional activation of mTOR and mTOR-dependent alterations in neuronal morphology. Neuronal size was determined in human specimens harboring DEPDC5 or NPRL3 mutations resected for epilepsy treatment. DEPDC5/NPRL3 KD effects on cell size, filopodial extension, subcellular mTOR complex 1 (mTORC1) localization, and mTORC1 activation during nutrient deprivation were assayed in mouse neuroblastoma cells (N2aC) and mouse subventricular zone derived neural progenitor cells (mNPCs). mTORC1-dependent effects of DEPDC5/NPRL3 KD were determined using the mTOR inhibitor rapamycin. Changes in mTOR subcellular localization and mTORC1 pathway activation following DEPDC5/NPRL3 KD were determined by examining the proximity of mTOR to the lysosomal surface during amino acid starvation. Neurons exhibiting PS6 immunoreactivity (Ser 235/236) in human specimens were 1.5× larger than neurons in post-mortem control samples. DEPDC5/NPRL3 KD caused mTORC1, but not mTORC2, hyperactivation, soma enlargement, and increased filopodia in N2aC and mNPCs compared with wildtype cells. DEPDC5/NPRL3 KD led to inappropriate mTOR localization at the lysosome along with constitutive mTOR activation following amino acid deprivation. DEPDC5/NPRL3 KD effects on morphology and functional mTOR activation were reversed by rapamycin. mTOR-dependent effects of DEPDC5/NPRL3 KD on morphology and subcellular localization of mTOR in neurons suggests that loss-of-function in GATOR1 subunits may play a role in MCD formation during fetal brain development. [ABSTRACT FROM AUTHOR]

The identification of pathogenic mutations in Ras analog in brain 39B (RAB39B) and Ras analog in brain 32 (RAB32) that cause Parkinson's disease (PD) has highlighted the emerging role of protein trafficking in disease pathogenesis. Ras analog in brain (Rab) Guanosine triphosphatase (GTPase) function as master regulators of membrane trafficking, including vesicle formation, movement along cytoskeletal networks, and membrane fusion. Recent studies have linked Rab GTPases with α-synuclein, Leucine-rich repeat kinase 2, and Vacuolar protein sorting 35, 3 key proteins in PD pathogenesis. In this review, we discuss the various RAB GTPases associated with PD, current progress in the research, and potential future directions. Investigations into the function of RAB GTPases will likely provide significant insight into the etiology of PD and identify novel therapeutic targets for a currently incurable disease. © 2018 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Objective: To characterize the clinical features and neuropathology associated with recessive VAC14 mutations. Methods: Whole-exome sequencing was used to identify the genetic etiology of a rapidly progressive neurological disease presenting in early childhood in two deceased siblings with distinct neuropathological features on post mortem examination. Results: We identified compound heterozygous variants in VAC14 in two deceased siblings with early childhood onset of severe, progressive dystonia, and neurodegeneration. Their clinical phenotype is consistent with the VAC14-related childhood-onset, striatonigral degeneration recently described in two unrelated children. Post mortem examination demonstrated prominent vacuolation associated with degenerating neurons in the caudate nucleus, putamen, and globus pallidus, similar to previously reported ex vivo vacuoles seen in the late-endosome/lysosome of VAC14-deficient neurons. We identified upregulation of ubiquitinated granules within the cell cytoplasm and lysosomal-associated membrane protein (LAMP2) around the vacuole edge to suggest a process of vacuolation of lysosomal structures associated with active autophagocytic-associated neuronal degeneration. Interpretation: Our findings reveal a distinct clinicopathological phenotype associated with recessive VAC14 mutations. [ABSTRACT FROM AUTHOR]

Defects in mRNA export from the nucleus have been linked to various neurodegenerative disorders. We report mutations in the gene MCM3AP, encoding the germinal center associated nuclear protein (GANP), in nine affected individuals from five unrelated families. The variants were associated with severe childhood onset primarily axonal (four families) or demyelinating (one family) Charcot-Marie-Tooth neuropathy. Mild to moderate intellectual disability was present in seven of nine affected individuals. The affected individuals were either compound heterozygous or homozygous for different MCM3AP variants, which were predicted to cause depletion of GANP or affect conserved amino acids with likely importance for its function. Accordingly, fibroblasts of affected individuals from one family demonstrated severe depletion of GANP. GANP has been described to function as an mRNA export factor, and to suppress TDP-43-mediated motor neuron degeneration in flies. Thus our results suggest defective mRNA export from nucleus as a potential pathogenic mechanism of axonal degeneration in these patients. The identification of MCM3AP variants in affected individuals from multiple centres establishes it as a disease gene for childhood-onset recessively inherited Charcot-Marie-Tooth neuropathy with intellectual disability. [ABSTRACT FROM AUTHOR]

Objective To explore the diagnostic utility and cost effectiveness of whole exome sequencing ( WES) in a cohort of individuals with peripheral neuropathy. Methods Singleton WES was performed in individuals recruited though one pediatric and one adult tertiary center between February 2014 and December 2015. Initial analysis was restricted to a virtual panel of 55 genes associated with peripheral neuropathies. Patients with uninformative results underwent expanded analysis of the WES data. Data on the cost of prior investigations and assessments performed for diagnostic purposes in each patient was collected. Results Fifty patients with a peripheral neuropathy were recruited (median age 18 years; range 2-68 years). The median time from initial presentation to study enrollment was 6 years 9 months (range 2 months-62 years), and the average cost of prior investigations and assessments for diagnostic purposes AU$4013 per patient. Eleven individuals received a diagnosis from the virtual panel. Eight individuals received a diagnosis following expanded analysis of the WES data, increasing the overall diagnostic yield to 38%. Two additional individuals were diagnosed with pathogenic copy number variants through SNP microarray. Conclusions This study provides evidence that WES has a high diagnostic utility and is cost effective in patients with a peripheral neuropathy. Expanded analysis of WES data significantly improves the diagnostic yield in patients in whom a diagnosis is not found on the initial targeted analysis. This is primarily due to diagnosis of conditions caused by newly discovered genes and the resolution of complex and atypical phenotypes. [ABSTRACT FROM AUTHOR]

Disturbed mitochondrial fusion and fission have been linked to various neurodegenerative disorders. In siblings from two unrelated families who died soon after birth with a profound neurodevelopmental disorder characterized by pontocerebellar hypoplasia and apnoea, we discovered a missense mutation and an exonic deletion in the SLC25A46 gene encoding a mitochondrial protein recently implicated in optic atrophy spectrum disorder. We performed functional studies that confirmed the mitochondrial localization and pro-fission properties of SLC25A46. Knockdown of slc24a46 expression in zebrafish embryos caused brain malformation, spinal motor neuron loss, and poor motility. At the cellular level, we observed abnormally elongated mitochondria, which was rescued by co-injection of the wild-type but not the mutant slc25a46 mRNA. Conversely, overexpression of the wild-type protein led to mitochondrial fragmentation and disruption of the mitochondrial network. In contrast to mutations causing non-lethal optic atrophy, missense mutations causing lethal congenital pontocerebellar hypoplasia markedly destabilize the protein. Indeed, the clinical severity appears inversely correlated with the relative stability of the mutant protein. This genotype-phenotype correlation underscores the importance of SLC25A46 and fine tuning of mitochondrial fission and fusion in pontocerebellar hypoplasia and central neurodevelopment in addition to optic and peripheral neuropathy across the life span. [ABSTRACT FROM AUTHOR]

We describe first cousin sibling pairs with focal epilepsy, one of each pair having focal cortical dysplasia (FCD) IIa. Linkage analysis and whole-exome sequencing identified a heterozygous germline frameshift mutation in the gene encoding nitrogen permease regulator-like 3 (NPRL3). NPRL3 is a component of GAP Activity Towards Rags 1, a negative regulator of the mammalian target of rapamycin complex 1 signaling pathway. Immunostaining of resected brain tissue demonstrated mammalian target of rapamycin activation. Screening of 52 unrelated individuals with FCD identified 2 additional patients with FCDIIa and germline NPRL3 mutations. Similar to DEPDC5, NPRL3 mutations may be considered as causal variants in patients with FCD or magnetic resonance imaging-negative focal epilepsy. [ABSTRACT FROM AUTHOR]

Whole-exome sequencing of two brothers with drug-resistant, early-onset, focal epilepsy secondary to extensive type IIA focal cortical dysplasia identified a paternally inherited, nonsense variant of DEPDC5 (c.C1663T, p.Arg555*). This variant has previously been reported to cause familial focal epilepsy with variable foci in patients with normal brain imaging. Immunostaining of resected brain tissue from both brothers demonstrated mammalian target of rapamycin ( mTOR) activation. This report shows the histopathological features of cortical dysplasia associated with a DEPDC5 mutation, confirms mTOR dysregulation in the malformed tissue and expands the spectrum of neurological manifestations of DEPDC5 mutations to include severe phenotypes with large areas of cortical malformation. [ABSTRACT FROM AUTHOR]

Copy number variants (CNVs) are associated with many neurocognitive disorders; however, these events are typically large, and the underlying causative genes are unclear. We created an expanded CNV morbidity map from 29,085 children with developmental delay in comparison to 19,584 healthy controls, identifying 70 significant CNVs. We resequenced 26 candidate genes in 4,716 additional cases with developmental delay or autism and 2,193 controls. An integrated analysis of CNV and single-nucleotide variant (SNV) data pinpointed 10 genes enriched for putative loss of function. Follow-up of a subset of affected individuals identified new clinical subtypes of pediatric disease and the genes responsible for disease-associated CNVs. These genetic changes include haploinsufficiency of SETBP1 associated with intellectual disability and loss of expressive language and truncations of ZMYND11 in individuals with autism, aggression and complex neuropsychiatric features. This combined CNV and SNV approach facilitates the rapid discovery of new syndromes and genes involved in neuropsychiatric disease despite extensive genetic heterogeneity. [ABSTRACT FROM AUTHOR]

Neurodegenerative disorders such as Friedreich ataxia (FRDA) present significant challenges in developing effective therapeutic intervention. Current treatments aim to manage symptoms and thus improve quality of life, but none can cure, nor are proven to slow, the neurodegeneration inherent to this disease. The primary clinical features of FRDA include progressive ataxia and shortened life span, with complications of cardiomyopathy being the major cause of death. FRDA is most commonly caused by an expanded GAA trinucleotide repeat in the first intron of FXN that leads to reduced levels of frataxin, a mitochondrial protein important for iron metabolism. The GAA expansion in FRDA does not alter the coding sequence of FXN. It results in reduced production of structurally normal frataxin, and hence any increase in protein level is expected to be therapeutically beneficial. Recently, there has been increased interest in developing novel therapeutic applications like cell and/or gene therapies, and these cutting-edge applications could provide effective treatment options for FRDA. Importantly, since individuals with FRDA produce frataxin at low levels, increased expression should not elicit an immune response. Here we review the advances to date and highlight the future potential for cell and gene therapy to treat this debilitating disease. [ABSTRACT FROM AUTHOR]

Borrone Dermato-Cardio-Skeletal (BDCS) syndrome is a severe progressive autosomal recessive disorder characterized by coarse facies, thick skin, acne conglobata, dysmorphic facies, vertebral abnormalities and mitral valve prolapse. We identified a consanguineous kindred with a child clinically diagnosed with BDCS. Linkage analysis of this family (BDCS1) identified five regions homozygous by descent with a maximum LOD score of 1.75. Linkage analysis of the family that originally defined BDCS (BDCS3) identified an overlapping linkage peak at chromosome 5q35.1. Sequence analysis identified two different homozygous mutations in BDCS1 and BDCS3, affecting the gene encoding the protein SH3 and PX domains 2B (SH3PXD2B), which localizes to 5q35.1. Western blot analysis of patient fibroblasts derived from affected individuals in both families demonstrated complete loss of SH3PXD2B. Homozygosity mapping and sequence analysis in a second published BDCS family (BDCS2) excluded SH3PXD2B. SH3PXD2B is required for the formation of functional podosomes, and loss-of-function mutations in SH3PXD2B have recently been shown to underlie 7 of 13 families with Frank-Ter Haar syndrome (FTHS). FTHS and BDCS share some overlapping clinical features; therefore, our results demonstrate that a proportion of BDCS and FTHS cases are allelic. Mutations in other gene(s) functioning in podosome formation and regulation are likely to underlie the SH3PXD2B-mutation-negative BDSC/FTHS patients. [ABSTRACT FROM AUTHOR]