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Objective Dominant optic atrophy (DOA) is the most common inherited optic neuropathy, with a prevalence of 1:12,000 to 1:25,000. OPA1 mutations are found in 70% of DOA patients, with a significant number remaining undiagnosed. Methods We screened 286 index cases presenting optic atrophy, negative for OPA1 mutations, by targeted next generation sequencing or whole exome sequencing. Pathogenicity and molecular mechanisms of the identified variants were studied in yeast and patient-derived fibroblasts. Results Twelve cases (4%) were found to carry novel variants in AFG3L2, a gene that has been associated with autosomal dominant spinocerebellar ataxia 28 (SCA28). Half of cases were familial with a dominant inheritance, whereas the others were sporadic, including de novo mutations. Biallelic mutations were found in 3 probands with severe syndromic optic neuropathy, acting as recessive or phenotype-modifier variants. All the DOA-associated AFG3L2 mutations were clustered in the ATPase domain, whereas SCA28-associated mutations mostly affect the proteolytic domain. The pathogenic role of DOA-associated AFG3L2 mutations was confirmed in yeast, unraveling a mechanism distinct from that of SCA28-associated AFG3L2 mutations. Patients' fibroblasts showed abnormal OPA1 processing, with accumulation of the fission-inducing short forms leading to mitochondrial network fragmentation, not observed in SCA28 patients' cells. Interpretation This study demonstrates that mutations in AFG3L2 are a relevant cause of optic neuropathy, broadening the spectrum of clinical manifestations and genetic mechanisms associated with AFG3L2 mutations, and underscores the pivotal role of OPA1 and its processing in the pathogenesis of DOA. ANN NEUROL 2020 ANN NEUROL 2020;88:18-32.

Biallelic mutations in the C1QBP gene have been associated with mitochondrial cardiomyopathy and combined respiratory-chain deficiencies, with variable onset (including intrauterine or neonatal forms), phenotypes, and severity. We studied two unrelated adult patients from consanguineous families, presenting with progressive external ophthalmoplegia (PEO), mitochondrial myopathy, and without any heart involvement. Muscle biopsies from both patients showed typical mitochondrial alterations and the presence of multiple mitochondrial DNA deletions, whereas biochemical defects of the respiratory chain were present only in one subject. Using next-generation sequencing approaches, we identified homozygous mutations in C1QBP. Immunoblot analyses in patients' muscle samples revealed a strong reduction in the amount of the C1QBP protein and varied impairment of respiratory chain complexes, correlating with disease severity. Despite the original study indicated C1QBP mutations as causative for mitochondrial cardiomyopathy, our data indicate that mutations in C1QBP have to be considered in subjects with PEO phenotype or primary mitochondrial myopathy and without cardiomyopathy.

The 2-oxoglutarate dehydrogenase-like (OGDHL) protein is a rate-limiting enzyme in the Krebs cycle that plays a pivotal role in mitochondrial metabolism. OGDHL expression is restricted mainly to the brain in humans. Here, we report nine individuals from eight unrelated families carrying bi-allelic variants in OGDHL with a range of neurological and neurodevelopmental phenotypes including epilepsy, hearing loss, visual impairment, gait ataxia, microcephaly, and hypoplastic corpus callosum. The variants include three homozygous missense variants (p.Pro852Ala, p.Arg244Trp, and p.Arg299Gly), three compound heterozygous single-nucleotide variants (p.Arg673Gln/p.Val488Val, p.Phe734Ser/p.Ala327Val, and p.Trp220Cys/p.Asp491Val), one homozygous frameshift variant (p.Cys553Leufs∗16), and one homozygous stop-gain variant (p.Arg440Ter). To support the pathogenicity of the variants, we developed a novel CRISPR-Cas9-mediated tissue-specific knockout with cDNA rescue system for dOgdh, the Drosophila ortholog of human OGDHL. Pan-neuronal knockout of dOgdh led to developmental lethality as well as defects in Krebs cycle metabolism, which was fully rescued by expression of wild-type dOgdh. Studies using the Drosophila system indicate that p.Arg673Gln, p.Phe734Ser, and p.Arg299Gly are severe loss-of-function alleles, leading to developmental lethality, whereas p.Pro852Ala, p.Ala327Val, p.Trp220Cys, p.Asp491Val, and p.Arg244Trp are hypomorphic alleles, causing behavioral defects. Transcript analysis from fibroblasts obtained from the individual carrying the synonymous variant (c.1464T>C [p.Val488Val]) in family 2 showed that the synonymous variant affects splicing of exon 11 in OGDHL. Human neuronal cells with OGDHL knockout exhibited defects in mitochondrial respiration, indicating the essential role of OGDHL in mitochondrial metabolism in humans. Together, our data establish that the bi-allelic variants in OGDHL are pathogenic, leading to a Mendelian neurodevelopmental disease in humans.

Many studies based on chromosomal microarray and next-generation sequencing (NGS) have identified hundreds of genes associated with autism spectrum disorder (ASD) risk, demonstrating that there are several complex genetic factors that contribute to ASD risk. We performed targeted NGS gene panels for 120 selected genes, in a clinical population of 40 children with well-characterized ASD. The variants identified were annotated and filtered, focusing on rare variants with a minimum allele frequency &lt, 1% in GnomAD. We found 147 variants in 39 of the 40 patients. It was possible to perform family segregation analysis in 28 of the 40 patients. We found 4 de novo and 101 inherited variants. For the inherited variants, we observed that all the variants identified in the patients came equally from the paternal and maternal genetic makeup. We identified 9 genes that are more frequently mutated than the others, and upon comparing the mutational frequency of these 9 genes in our cohort and the mutational frequency in the GnomAD population, we found significantly increased frequencies of rare variants in our study population. This study supports the hypothesis that ASD is the result of a combination of rare deleterious variants (low contribution) and many low-risk alleles (genetic background), highlighting the importance of MET and SLIT3 and the potentially stronger involvement of FAT1 and VPS13B in ASD. Taken together, our findings reinforce the importance of using gene panels to understand the contribution of the different genes already associated with ASD in the pathogenesis of the disease.

Editorial on the Research Topic Application of Omics Approaches to the Diagnosis of Genetic Neurological Disorders Neurological disorders comprise a huge variety of complex diseases, affecting the nervous systems and the skeletal muscle, which represent major causes of death and disability worldwide. Variants in a rapidly expanding number of genes involved in a broad variety of cellular functions are causally linked to a significant proportion of neurological disorders, acting alone or in combination with environmental factors. Over the past few years, the application of the different high-throughput approaches, also known as omics approaches (e.g., genomics, transcriptomics, proteomics, and metabolomics), has developed rapidly and revolutionized both the diagnosis and the understanding of the pathophysiology of neurological disorders, by providing un unbiased identification of disease-causing gene variants, biomarkers, and targets for potential therapeutic strategies. Omics techniques have been widely used in the past to research the genetic and molecular basis of neurological disorders. Today, given their rapidly decreasing costs, the increasing standardization of protocols, and the rapid turn-around time, these technologies are emerging also as a powerful addition to standard diagnostic procedures. In this Research Topic four original papers highlight the potentialities of omics approaches in the diagnosis of genetic neurological disorders. One of the most powerful diagnostic tool based on Next Generation Sequencing (NGS) is represented by targeted gene panels. Targeted re-sequencing using custom-made panels is highly efficient for the screening of up to hundreds potentially clinically relevant genes. This approach allows to perform genetic analysis in large cohorts of patients with affordable costs within a short timeframe, with the advantage of generating relatively low amount of data and easy to interpret results. In this Research Topic, to highlight the importance of targeted gene panels in the genetic diagnosis of neurological disorders, a study based on the genetic screening of more than 1,000 patients affected by autosomal optic atrophy have been included (Charif et al.). Going beyond gene panels, a Whole Exome Sequencing (WES) approach allows the sequencing of all exons and exon-intron boundaries for all protein-coding genes in the genome. Its massive application in the last decade has dramatically increased the pace of disease gene discovery. The extensive, unbiased approach of WES usually lead to identification of around 20,000 coding variants per individuals, thus the analysis of results requires more advanced and complex strategies compared to targeted panel NGS. Often the interpretation of WES results needs to be integrated with additional available information such as clinical, metabolic, neuroimaging and biochemical data. However, WES approach can represent a powerful diagnostic tool in familiar cases, especially when a detailed clinical description and DNA samples from multiple family members are available. This is demonstrated by the case report added in our Research Topic, in which WES successfully identified a disease causing variant in a consanguineous family affected by spastic quadriplegia (Elsayed et al.). In order to better characterize hidden genotype-phenotype correlations, it is crucial to develop integrative approaches that combine biological information coming from different sources to highlight the interrelationships of the involved biomolecules and their functions. This strategy can provide insights in the understanding, the diagnosis, the treatment of neurological diseases, and explore the boundaries of personalized medicine. For example, extracting and integrating heterogeneous information from neuroimaging and genomics can contribute to better define the correlation between neurological presentations and genetic alterations, improving the diagnostic process for several pathological conditions affecting the nervous system. This type of approach has been performed for the diagnosis of neuronal intranuclear inclusion in an original research article included in this Research Topic (Pang et al.). In addition to genomics, also proteomics technology offers great promise in the understanding and treatment of the molecular basis of neurological diseases. Pathological conditions are the result of protein dysfunctions resulting from alterations of protein structure, abundance, activity, and/or interactions. The fast growing field of clinical proteomics aims to decipher protein changes associated to a specific disease, thereby providing ideal biomarkers for diagnosis, prognosis, and prediction of therapeutic response. Mainly based on its enormous hypothetical relevance, clinical proteomics is an ever-growing field. In the present Research Topic we included an original research article describing the use of proteomics for the identification of new potential biomarkers associated with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) (Morani et al.). Pathogenic variants discovered in research cohorts of genetic diseases are ultra-rare and usually private to a family, highlighting the need to ensure that non-European populations are included in gene discovery efforts. Furthermore, it also emphasizes the need to use population specific allele frequencies to ensure variants are interpreted in the correct context. This Research Topic was diverse not only in genomic technologies outlined above but also included studies from Chinese (Pang et al.) and Sudanese (Elsayed et al.) populations. This Research Topic would not have been possible without the contributions of several people. We would like to thank the authors of the submitted manuscripts for their precious studies and valuable data. We also thank the staff of Frontiers in Neurology for their dedicated assistance and support. AL, EG, MS, and ML had the role of guest associate editors for the...

Mitochondria are highly dynamic organelles, undergoing continuous fission and fusion. The DNM1L (dynamin-1 like) gene encodes for the DRP1 protein, an evolutionary conserved member of the dynamin family, responsible for fission of mitochondria, and having a role in the division of peroxisomes, as well. DRP1 impairment is implicated in several neurological disorders and associated with either de novo dominant or compound heterozygous mutations. In five patients presenting with severe epileptic encephalopathy, we identified five de novo dominant DNM1L variants, the pathogenicity of which was validated in a yeast model. Fluorescence microscopy revealed abnormally elongated mitochondria and aberrant peroxisomes in mutant fibroblasts, indicating impaired fission of these organelles. Moreover, a very peculiar finding in our cohort of patients was the presence, in muscle biopsy, of core like areas with oxidative enzyme alterations, suggesting an abnormal distribution of mitochondria in the muscle tissue.

Here we report on a singleton patient affected by a complicated congenital syndrome characterized by growth delay, retinal dystrophy, sensorineural deafness, myopathy, ataxia, combined pituitary hormone deficiency, associated with mitochondrial impairment. Targeted clinical exome sequencing led to the identification of a homozygous missense variant in OTX2. Since only dominant mutations within OTX2 have been associated with cases of syndromic microphthalmia, retinal dystrophy with or without pituitary dysfunctions, this represents the first report of an OTX2 recessive mutation. Part of the phenotype, including ataxia, myopathy and multiple mitochondrial respiratory chain defects, seemed not related to OTX2. Further analysis of next generation sequencing (NGS) data revealed additional candidate variants: a homozygous variant in LETM1, and heterozygous rare variants in AFG3L2 and POLG. All three genes encode mitochondrial proteins and the last two are known to be associated with ataxia, a neurological sign present also in the father of the proband. With our study, we aim to encourage the integration of NGS data with a detailed analysis of clinical description and family history in order to unravel composite genotypes sometimes associated with complicated phenotypes.

Pearson marrow pancreas syndrome (PMPS) is a sporadic mitochondrial disease, resulting from the clonal expansion of a mutated mitochondrial DNA (mtDNA) molecule bearing a macro-deletion, and therefore missing essential genetic information. PMPS is characterized by the presence of deleted (Δ) mtDNA that co-exist with the presence of a variable amount of wild-type mtDNA, a condition termed heteroplasmy. All tissues of the affected individual, including the haemopoietic system and the post-mitotic, highly specialized tissues (brain, skeletal muscle, and heart) contain the large-scale mtDNA deletion in variable amount. We generated human induced pluripotent stem cells (hiPSCs) from two PMPS patients, carrying different type of large-scale deletion.

Leigh syndrome is a progressive neurodegenerative disorder, most commonly observed in paediatric mitochondrial disease, and is often associated with pathogenic variants in complex I structural subunits or assembly factors resulting in isolated respiratory chain complex I deficiency. Clinical heterogeneity has been reported, but key diagnostic findings are developmental regression, elevated lactate and characteristic neuroimaging abnormalities. Here, we describe three affected children from two unrelated families who presented with Leigh syndrome due to homozygous variants (c.346_*7del and c.173A>T p.His58Leu) in NDUFC2, encoding a complex I subunit. Biochemical and functional investigation of subjects’ fibroblasts confirmed a severe defect in complex I activity, subunit expression and assembly. Lentiviral transduction of subjects’ fibroblasts with wild‐type NDUFC2 cDNA increased complex I assembly supporting the association of the identified NDUFC2 variants with mitochondrial pathology. Complexome profiling confirmed a loss of NDUFC2 and defective complex I assembly, revealing aberrant assembly intermediates suggestive of stalled biogenesis of the complex I holoenzyme and indicating a crucial role for NDUFC2 in the assembly of the membrane arm of complex I, particularly the ND2 module., This work describes the first confirmed pathogenic variants in NDUFC2 in a case of mitochondrial disease presenting with symptoms of Leigh syndrome and a severe deficiency in OXPHOS complex I. NDUFC2 was shown to be important for the assembly of the membrane arm of complex I.

Next Generation Sequencing (NGS) technologies are revolutionizing the diagnostic screening for rare disease entities, including primary mitochondrial disorders, particularly those caused by nuclear gene defects. NGS approaches are able to identify the causative gene defects in small families and even single individuals, unsuitable for investigation by traditional linkage analysis. These technologies are contributing to fill the gap between mitochondrial disease cases defined on the basis of clinical, neuroimaging and biochemical readouts, which still outnumber by approximately 50% the cases for which a molecular-genetic diagnosis is attained. We have been using a combined, two-step strategy, based on targeted genes panel as a first NGS screening, followed by whole exome sequencing (WES) in still unsolved cases, to analyze a large cohort of subjects, that failed to show mutations in mtDNA and in ad hoc sets of specific nuclear genes, sequenced by the Sanger's method. Not only this approach has allowed us to reach molecular diagnosis in a significant fraction (20%) of these difficult cases, but it has also revealed unexpected and conceptually new findings. These include the possibility of marked variable penetrance of recessive mutations, the identification of large-scale DNA rearrangements, which explain spuriously heterozygous cases, and the association of mutations in known genes with unusual, previously unreported clinical phenotypes. Importantly, WES on selected cases has unraveled the presence of pathogenic mutations in genes encoding non-mitochondrial proteins (e.g. the transcription factor E4F1), an observation that further expands the intricate genetics of mitochondrial disease and suggests a new area of investigation in mitochondrial medicine. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

This study focused on the molecular characterization of patients with leukoencephalopathy associated with a specific biochemical defect of mitochondrial respiratory chain complex III, and explores the impact of a distinct magnetic resonance imaging pattern of leukoencephalopathy to detect biallelic mutations in LYRM7 in patients with biochemically unclassified leukoencephalopathy. ‘Targeted resequencing’ of a custom panel including genes coding for mitochondrial proteins was performed in patients with complex III deficiency without a molecular genetic diagnosis. Based on brain magnetic resonance imaging findings in these patients, we selected additional patients from a database of unclassified leukoencephalopathies who were scanned for mutations in LYRM7 by Sanger sequencing. Targeted sequencing revealed homozygous mutations in LYRM7 , encoding mitochondrial LYR motif-containing protein 7, in four patients from three unrelated families who had a leukoencephalopathy and complex III deficiency. Two subjects harboured previously unreported variants predicted to be damaging, while two siblings carried an already reported pathogenic homozygous missense change. Sanger sequencing performed in the second cohort of patients revealed LYRM7 mutations in three additional patients, who were selected on the basis of the magnetic resonance imaging pattern. All patients had a consistent magnetic resonance imaging pattern of progressive signal abnormalities with multifocal small cavitations in the periventricular and deep cerebral white matter. Early motor development was delayed in half of the patients. All patients but one presented with subacute neurological deterioration in infancy or childhood, preceded by a febrile infection, and most patients had repeated episodes of subacute encephalopathy with motor regression, irritability and stupor or coma resulting in major handicap or death. LYRM7 protein was strongly reduced in available samples from patients; decreased complex III holocomplex was observed in fibroblasts from a patient carrying a splice site variant; functional studies in yeast confirmed the pathogenicity of two novel mutations. Mutations in LYRM7 were previously found in a single patient with a severe form of infantile onset encephalopathy. We provide new molecular, clinical, and neuroimaging data allowing us to characterize more accurately the molecular spectrum of LYRM7 mutations highlighting that a distinct and recognizable magnetic resonance imaging pattern is related to mutations in this gene. Inter- and intrafamilial variability exists and we observed one patient who was asymptomatic by the age of 6 years.

Background KARS encodes lysyl- transfer ribonucleic acid (tRNA) synthetase, which catalyzes the aminoacylation of tRNA-Lys in the cytoplasm and mitochondria. Eleven families/sporadic patients and 16 different mutations in KARS have been reported to date. The associated clinical phenotype is heterogeneous ranging from early onset encephalopathy to isolated peripheral neuropathy or nonsyndromic hearing impairment. Recently additional presentations including leukoencephalopathy as predominant cerebral involvement or cardiomyopathy, isolated or associated with muscular and cerebral involvement, have been reported. A progressive Leukoencephalopathy with brainstem and spinal cord calcifications was previously described in a singleton patient and in two siblings, without the identification of the genetic cause. We reported here about a new severe phenotype associated with biallelic KARS mutations and sharing some common points with the other already reported phenotypes, but with a distinct clinical and neuroimaging picture. Review of KARS mutant patients published to date will be also discussed. Results Herein, we report the clinical, biochemical and molecular findings of 2 unreported Italian patients affected by developmental delay, acquired microcephaly, spastic tetraparesis, epilepsy, sensory-neural hypoacusia, visual impairment, microcytic hypochromic anaemia and signs of hepatic dysfunction. MRI pattern in our patients was characterized by progressive diffuse leukoencephalopathy and calcifications extending in cerebral, brainstem and cerebellar white matter, with spinal cord involvement. Genetic analysis performed on these 2 patients and in one subject previously described with similar MRI pattern revealed the presence of biallelic mutations in KARS in all 3 subjects. Conclusions With our report we define the molecular basis of the previously described Leukoencephalopathy with Brainstem and Spinal cord Calcification widening the spectrum of KARS related disorders, particularly in childhood onset disease suggestive for mitochondrial impairment. The review of previous cases does not suggest a strict and univocal genotype/phenotype correlation for this highly heterogeneous entity. Moreover, our cases confirm the usefulness of search for common brain and spine MR imaging pattern and of broad genetic screening, in syndromes clinically resembling mitochondrial disorders in spite of normal biochemical assay. Electronic supplementary material The online version of this article (10.1186/s13023-018-0788-4) contains supplementary material, which is available to authorized users.

Biallelic mutations in NDUFAF6 have been identified as responsible for cases of autosomal recessive Leigh syndrome associated with mitochondrial complex I deficiency. Here we report two siblings and two unrelated subjects with Leigh syndrome, in which we found the same compound heterozygous missense (c.532G>C:p.A178P) and deep intronic (c.420+784C>T) variants in NDUFAF6. We demonstrated that the identified intronic variant creates an alternative splice site, leading to the production of an aberrant transcript. A detailed analysis of whole-exome sequencing data together with the functional validation based on mRNA analysis may reveal pathogenic variants even in non-exonic regions.

Background Hereditary myopathy with lactic acidosis and myopathy with deficiency of succinate dehydrogenase and aconitase are variants of a recessive disorder characterised by childhood-onset early fatigue, dyspnoea and palpitations on trivial exercise. The disease is non-progressive, but life-threatening episodes of widespread weakness, metabolic acidosis and rhabdomyolysis may occur. So far, this disease has been molecularly defined only in Swedish patients, all homozygous for a deep intronic splicing affecting mutation in ISCU encoding a scaffold protein for the assembly of iron–sulfur (Fe-S) clusters. A single Scandinavian family was identified with a different mutation, a missense change in compound heterozygosity with the common intronic mutation. The aim of the study was to identify the genetic defect in our proband. Methods A next-generation sequencing (NGS) approach was carried out on an Italian male who presented in childhood with ptosis, severe muscle weakness and exercise intolerance. His disease was slowly progressive, with partial recovery between episodes. Patient’s specimens and yeast models were investigated. Results Histochemical and biochemical analyses on muscle biopsy showed multiple defects affecting mitochondrial respiratory chain complexes. We identified a single heterozygous mutation p.Gly96Val in ISCU , which was absent in DNA from his parents indicating a possible de novo dominant effect in the patient. Patient fibroblasts showed normal levels of ISCU protein and a few variably affected Fe-S cluster-dependent enzymes. Yeast studies confirmed both pathogenicity and dominance of the identified missense mutation. Conclusion We describe the first heterozygous dominant mutation in ISCU which results in a phenotype reminiscent of the recessive disease previously reported.

The classic features of deoxyguanosine kinase (DGUOK) deficiency are infantile onset hepatic failure with nystagmus and hypotonia; mitochondrial DNA studies on affected tissue reveal mitochondrial DNA depletion. Later, it has been shown that the mutations in the same gene may present with adult-onset mitochondrial myopathy and mitochondrial DNA multiple deletions in skeletal muscle. Here we report the case of a 42-year-old Italian woman presenting with a chronic progressive external ophthalmoplegia and myopathy with mtDNA multiple deletions and the compound heterozygous c.462T>A (p.Asn154Lys) and c.707+2T>G pathogenic variants in DGUOK.

A 60-year-old man is presented with progressive involuntary muscle movements and neuropsychiatric symptoms who developed a variety of additional complaints over 2 years. Brain imaging revealed bilateral basal ganglia calcifications suggesting primary familial brain calcification. Analysis of the SLC20A2 gene revealed a missense mutation (c.541C>T, p.(Arg181Trp)), in silico predicted to be deleterious and not found in available databases. Segregation analysis confirmed his asymptomatic father to harbor the same mutation, though on brain imaging basal ganglia calcifications were found. This report illustrates the intrafamilial variability of the phenotype and generalized myoclonus as the presenting symptom.

Mitochondrial Fission Factor (MFF) is part of a protein complex that promotes mitochondria and peroxisome fission. Hitherto, only 5 patients have been reported harboring mutations in MFF, all of them with the clinical features of a very early onset Leigh-like encephalopathy. We report on an 11-year-old boy with epileptic encephalopathy. He presented with neurological regression, epileptic myoclonic seizures, severe intellectual disability, microcephaly, tetraparesis, optic atrophy, and ophthalmoplegia. Brain MRI pattern was compatible with Leigh syndrome. NGS-based analysis of a gene panel for mitochondrial disorders revealed a homozygous c.892C>T (p. Arg298*) in the MFF gene. Fluorescence staining detected abnormal morphology of mitochondria and peroxisomes in fibroblasts from the patient; a strong reduction in MFF protein levels and the presence of truncated forms were observed. No biochemical alterations denoting peroxisomal disorders were found. As reported in other disorders affecting the dynamics of intracellular organelles, our patient showed clinical features suggesting both mitochondrial and peroxisomal impairment. High levels of lactate in our case suggested an involvement of the energetic metabolism but without clear respiratory chain deficiency, while biomarkers of peroxisomal dysfunction were normal. We confirm that MFF mutations are associated with epileptic encephalopathy with Leigh-like MRI pattern.

Background Heterozygous mutations in OPA1 are a common cause of autosomal dominant optic atrophy, sometimes associated with extra-ocular manifestations. Few cases harboring compound heterozygous OPA1 mutations have been described manifesting complex neurodegenerative disorders in addition to optic atrophy. Results We report here three patients: one boy showing an early-onset mitochondrial disorder with hypotonia, ataxia and neuropathy that was severely progressive, leading to early death because of multiorgan failure; two unrelated sporadic girls manifesting a spastic ataxic syndrome associated with peripheral neuropathy and, only in one, optic atrophy. Using a targeted resequencing of 132 genes associated with mitochondrial disorders, in two probands we found compound heterozygous mutations in OPA1: in the first a 5 nucleotide deletion, causing a frameshift and insertion of a premature stop codon (p.Ser64Asnfs*7), and a missense change (p.Ile437Met), which has recently been reported to have clinical impact; in the second, a novel missense change (p.Val988Phe) co-occurred with the p.Ile437Met substitution. In the third patient a homozygous mutation, c.1180G > A (p.Ala394Thr) in OPA1 was detected by a trio-based whole exome sequencing approach. One of the patients presented also variants in mitochondrial DNA that may have contributed to the peculiar phenotype. The deleterious effect of the identified missense changes was experimentally validated in yeast model. OPA1 level was reduced in available patients’ biological samples, and a clearly fragmented mitochondrial network was observed in patients’ fibroblasts. Conclusions This report provides evidence that bi-allelic OPA1 mutations may lead to complex and severe multi-system recessive mitochondrial disorders, where optic atrophy might not represent the main feature. Electronic supplementary material The online version of this article (doi:10.1186/s13023-017-0641-1) contains supplementary material, which is available to authorized users.

The FARS2 gene encodes the mitochondrial phenylalanyl-tRNA synthetase and is implicated in autosomal recessive combined oxidative phosphorylation deficiency 14, a clinical condition characterized by infantile onset epilepsy and encephalopathy. Mutations in FARS2 have been reported in only few patients, but a detailed description of seizures, electroencephalographic patterns, magnetic resonance imaging findings, and long-term follow-up is still needed. We provide a clinical report of a child with FARS2-related disease manifesting drug-resistant infantile spasms associated with focal seizures. By comparative genomic hybridization analysis we identified a heterozygous microdeletion in the short arm of chromosome 6, inherited from the mother, that encompasses the first coding exon of FARS2. By sequencing of the FARS2 gene we identified a variant c.1156C>G; p.(R386G), inherited from the father. By using standard spectrophotometric techniques in skin fibroblasts, we found a combined abnormality of complexes I and IV of the mitochondrial respiratory chain. The main clinical features of the patient included axial hypotonia, mild distal hypertonia, and psychomotor delay. The magnetic resonance imaging showed microcephaly, frontal cerebral atrophy, and signal changes of dentate nuclei. At the age of 3 years and 6 months, the patient was still under treatment with vigabatrin and he has been seizure free for the last 23 months. © 2016 Wiley Periodicals, Inc.

International audience; Primary familial brain calcification (PFBC) is a rare cerebral microvascular calcifying disorder with a wide spectrum of motor, cognitive, and neuropsychiatric symptoms. It is typically inherited as an autosomal-dominant trait with four causative genes identified so far: SLC20A2, PDGFRB, PDGFB, and XPR1. Our study aimed at screening the coding regions of these genes in a series of 177 unrelated probands that fulfilled the diagnostic criteria for primary brain calcification regardless of their family history. Sequence variants were classified as pathogenic, likely pathogenic, or of uncertain significance (VUS), based on the ACMG-AMP recommendations. We identified 45 probands (25.4%) carrying either pathogenic or likely pathogenic variants (n = 34, 19.2%) or VUS (n = 11, 6.2%). SLC20A2 provided the highest contribution (16.9%), followed by XPR1 and PDGFB (3.4% each), and PDGFRB (1.7%). A total of 81.5% of carriers were symptomatic and the most recurrent symptoms were parkinsonism, cognitive impairment, and psychiatric disturbances (52.3%, 40.9%, and 38.6% of symptomatic individuals, respectively), with a wide range of age at onset (from childhood to 81 years). While the pathogenic and likely pathogenic variants identified in this study can be used for genetic counseling, the VUS will require additional evidence, such as recurrence in unrelated patients, in order to be classified as pathogenic.

A homoallelic missense founder mutation of the iron-sulfur cluster assembly 2 (ISCA2) gene has been recently reported in six cases affected by an autosomal recessive infantile neurodegenerative mitochondrial disorder. We documented a case of a 2-month-old girl presenting with severe hypotonia and nystagmus, who rapidly deteriorated and died at the age of three months. Increased cerebral spinal fluid level of lactate, documented also at the brain spectroscopy, involvement of the cortex, restricted diffusion of white and gray matter abnormalities, sparing of the corpus callosum and extensive involvement of the spinal cord were observed. Her clinical presenting features and course as well as some neuroradiological findings mimicked those of early-onset leukoencephalopathy with brainstem and spinal cord involvement and high brain lactate (LBSL). The analysis of the mitochondrial respiratory chain function showed a reduced activity of complexes II and IV. The girl harboured two heterozygous mutations in the ISCA2 gene. A comprehensive review of the literature and a comparison with the cases of early onset LBSL enabled us to highlight significant differences in the clinical, biochemical and neuroradiological phenotype between the two conditions, which also emerged from the comparison with the other 6 reported cases of ISCA2 gene mutation previously reported. In summary, this represents the second report ever published associating ISCA2 gene mutation with a mitochondrial leukoencephalopathy, with a different genetic mechanism to the previous cases. Molecular analysis of ISCA2 should be included in the genetic panel for the diagnosis of early onset mitochondrial leukoencephalopathies.

Aims Primary familial brain calcification (PFBC) is a rare disorder characterized by abnormal deposits of calcium in the basal ganglia and cerebellum. PFBC can present with a spectrum of neuropsychiatric symptoms resembling those seen in dementia and schizophrenia. Mutations in a few genes have been identified as causing PFBC: namely, the SLC20A2 gene that codes for the sodium-dependent phosphate transporter and the PDGFRB gene that codes for the platelet-derived growth factor receptor β (PDGF-Rβ). A recent study identified mutations in PDGFB coding for PDGF-B, the main ligand for PDGF-Rβ, in six families with PFBC. Here we report the first Japanese family with PFBC carrying a mutation in PDGFB, which causes the substitution of an arginine with a stop codon at amino acid 149 of the PDGF-B protein (p. Arg149*). Methods Clinical histories and computed tomography scan images were provided. Sanger sequencing was performed for the exome analysis of SLC20A2 and PDGFB genes. Results One family member began to complain of auditory hallucination at 16 years of age and had been treated for schizophrenia. His father suffered from memory and gait disturbances in his late 60s. A computed tomography scan revealed a symmetrical area of calcification over the basal ganglia in both cases. A known mutation in PDGFB (c.445C>T, p.Arg149*) was consistently detected in both PFBC cases by Sanger sequencing. No mutations in SLC20A2 were detected. Conclusions Our findings suggest that this mutation in PDGF-B is responsible for PFBC in this Japanese family and that abnormal PDGF signaling may be involved in the pathophysiology of certain psychiatric disorders.

To date, 3 AIFM1 (apoptosis inducing factor mitochondrial 1, located on Xq26.1) mutations have been reported: 2 missense changes (c.923G>A/p.Gly308Glu; c.1478A>T/p.Glu493Val) and a 3-basepair deletion (c.601delAGA/p.Arg201del). Two mutations have been described in early-onset severe mitochondrial encephalomyopathy related to impaired oxidative phosphorylation.(1,2) A third mutation is associated with Cowchock syndrome, or Charcot-Marie-Tooth X4 (CMTX4), a slowly progressive disorder characterized by axonal neuropathy, hearing loss, and mental retardation.(3,4

Patients with pathogenic truncating mutations in the prion gene (PRNP) usually present with prolonged disease courses with severe neurofibrillary tangle and cerebral amyloidosis pathology, but more atypical phenotypes also occur, including those with dysautonomia and peripheral neuropathy. We describe the neurological, cognitive, neuroimaging, and electrophysiological features of a31-year-old man presenting with an orbitofrontal syndrome, gastrointestinal symptoms, and peripheral neuropathy associated with PRNP Q160X nonsense mutation, with symptom onset at age 27. The mutation was also detected in his asymptomatic father and asymptomatic paternal cousin; several members of prior generations died from early onset dementia. This is the first report of afamily affected with the nonsense PRNP mutation Q160X displaying clear autosomal dominant disease in multiple family members and reduced penetrance. This case strengthens the evidence suggesting an association between PRNP truncating mutations and prion systemic amyloidosis. PRNP gene testing shouldbeconsidered in any patient with atypical dementia, especially with early onset and neuropathy, even in the absence of afamily history.

Primary familial brain calcification (PFBC) is a neurological disease characterized by calcium phosphate deposits in the basal ganglia and other brain regions and has thus far been associated with SLC20A2, PDGFB or PDGFRB mutations. We identified in multiple families with PFBC mutations in XPR1, a gene encoding a retroviral receptor with phosphate export function. These mutations alter phosphate export, implicating XPR1 and phosphate homeostasis in PFBC. Lung GO Sequencing Project Lung GO Sequencing Project Women's Health Initiative (WHI) Sequencing Project Broad GO Sequencing Project Seattle GO Sequencing Project Heart GO Sequencing Project United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Neurological Disorders & Stroke (NINDS) Association Francaise contre les Myopathies Ligue Nationale contre le Cancer (Comite de l'Herault) Fondation pour la Recherche Medicale FEDER European Union Languedoc-Roussillon grant National Institute of Neurological Disorders and Stroke Informatics Center for Neurogenetics and Neurogenomics Fondation pour la Recherche Medicale Institut National du Cancer (INCA) France Labex GR-Ex Labex EpiGenMed French National Research Agency (ANR) Institut National de la Sante et de la Recherche Medicale (Inserm) European Commission Instituto de Salud Carlos III (ISCIII) INNOPHARMA project MINECO-USC Servizo Galego de Saúde (SERGAS) National Council for Scientific and Technological Development (CNPq) United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Mental Health (NIMH) United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Neurological Disorders & Stroke (NINDS) University Hospital of Rouen French CNR-MAJ United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Heart Lung & Blood Institute (NHLBI) United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Mental Health (NIMH) United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Neurological Disorders & Stroke (NINDS)

Introduction Although TDP-43 is the main constituent of the ubiquitinated cytoplasmic inclusions in the most common forms of frontotemporal lobar degeneration, TARDBP mutations are not a common cause of familial frontotemporal dementia, especially in the absence of motor neuron disease. Results We describe a pedigree presenting with a complex autosomal dominant disease, with a heterogeneous clinical phenotype, comprising unspecified dementia, parkinsonism, frontotemporal dementia and motor neuron disease. Genetic analyses identified a novel P112H TARDBP double variation located in exon 3 coding for the first RNA recognition motif of the protein (RRM1). This double mutation is probably pathogenic based on neuropathological findings, in silico prediction analysis and exome sequencing. The two autopsied siblings described here presented with frontotemporal dementia involving multiple cognitive domains and behavior but lacking symptoms of motor neuron disease throughout the disease course. The siblings presented with strikingly similar, although atypical, neuropathological features, including an unclassifiable TDP-43 inclusion pattern, a high burden of tau-negative β-amyloid neuritic plaques with an AD-like biochemical profile, and an unclassifiable 4-repeat tauopathy. The co-occurrence of multiple protein inclusions points to a pathogenic mechanism that facilitates misfolded protein interaction and aggregation or a loss of TDP-43 function that somehow impairs protein clearance. Conclusions TARDBP mutation screening should be considered in familial frontotemporal dementia cases, even without signs or symptoms of motor neuron disease, especially when other more frequent causes of genetic frontotemporal dementia (i.e. GRN, C9ORF72, MAPT) have been excluded and when family history is complex and includes parkinsonism, motor neuron disease and frontotemporal dementia. Further investigations in this family may provide insight into the physiological functions of TARDBP. Electronic supplementary material The online version of this article (doi:10.1186/s40478-015-0190-6) contains supplementary material, which is available to authorized users.

A familial behavioral variant frontotemporal dementia associated with astrocyte-predominant tauopathy is described in 2 sisters born from consanguineous parents. The neuropathologic examination revealed massive accumulation of abnormally hyperphosphorylated, conformational, truncated tau at aspartic acid 421, ubiquitinated and nitrated tau at Tyr29 in cortical astrocyte (including their perivascular foot processes), and Bergmann glia. Smaller amounts of abnormal tau were observed in neurons and rarely in oligodendrocytes. There was decreased expression of glial glutamate transporter in the majority of tau-positive astrocytes. Gel electrophoresis of sarkosyl-insoluble fractions showed 2 bands of 64 and 60 kDa and a doublet of 67 to 70 kDa (which are different from those seen in Alzheimer disease and in typical 4R and 3R tauopathies) together with several bands of lower molecular weight indicative of truncated tau. Analysis of the expression of MAPT isoforms further revealed altered splicing and representation of tau isoforms involving exons 2, 3, and 10. Genetic testing revealed no known mutations in PSEN1, PSEN2, APP, MAPT, GRN, FUS, and TARDBP and no pathologic expansion in C9ORF72. However, a novel rare heterozygous sequence variant(p.Q140H) of uncertain significance was identified in FUS in both siblings.

We report about a patient with infantile-onset neurodegenerative disease associated with isolated mitochondrial respiratory chain complex III (cIII) deficiency. The boy, now 13 years old, presented with language regression and ataxia at 4 years of age and then showed a progressive course resulting in the loss of autonomous gait and speaking during the following 2 years. Brain MRI disclosed bilateral striatal necrosis. Sequencing of a panel containing nuclear genes associated with cIII deficiency revealed a previously undescribed homozygous rearrangement (c.782_786delinsGAAAAG) in TTC19 gene, which results in a frameshift with premature termination (p.Glu261Glyfs(*)8). TTC19 protein was absent in patient's fibroblasts. TTC19 encodes tetratricopeptide 19, a putative assembly factor for cIII. To date TTC19 mutations have been reported only in few cases, invariably associated with cIII deficiency, but presenting heterogeneous clinical phenotypes. We reviewed the genetic, biochemical, clinical and neuroradiological features of TTC19 mutant patients described to date.

Short-term studies have shown that octreotide, a long-acting somatostatin analog, blunts postprandial glycemic responses and reduces insulin requirement in insulin treated diabetic patients. The aim of our study was to investigate the effects of three single, different doses of octreotide on the glycemic response to a mixed meal in eight insulin treated type 2 diabetic patients after secondary failure with hypoglycemic agents. Previous treatments were substituted by regular insulin, 0.5 U/kg/day divided into three sc injections, for at least seven days. All patients received: (a) regular insulin (0.1 U/kg, sc) at 7.30 am; (b) octreotide 25 micrograms sc or (c) 50 micrograms sc or (d) 100 micrograms sc simultaneously with insulin but injected at different sites. From 8.00 to 8.15 the patients consumed a preconstituted fluid mixed meal of 250 ml. Following insulin alone a significant increase in blood glucose levels was observed after the meal. Abolished and not significantly different blood glucose responses to the meal after each of the three doses of octreotide were observed. Our findings suggest that with a low dose of octreotide (25 micrograms) it is possible to abolish the postprandial glycemic peak in type 2 diabetic patients treated with insulin.

Primary familial brain calcification (PFBC) is a heterogeneous neuropsychiatric disorder, with affected individuals presenting a wide variety of motor and cognitive impairments, such as migraine, parkinsonism, psychosis, dementia, and mood swings. Calcifications are usually symmetrical, bilateral, and found predominantly in the basal ganglia, thalamus, and cerebellum. So far, variants in three genes have been linked to PFBC: SLC20A2, PDGFRB, and PDGFB. Variants in SLC20A2 are responsible for most cases identified so far and, therefore, the present review is a comprehensive worldwide summary of all reported variants to date. SLC20A2 encodes an inorganic phosphate transporter, PiT-2, widely expressed in various tissues, including brain, and is part of a major family of solute carrier membrane transporters. Fifty variants reported in 55 unrelated patients so far have been identified in families of diverse ethnicities and only few are recurrent. Various types of variants were detected (missense, nonsense, frameshift) including full or partial SLC20A2 deletions. The recently reported SLC20A2 knockout mouse will enhance our understanding of disease mechanism and allow for screening of therapeutic compounds. In the present review, we also discuss the implications of these recent exciting findings and consider the possibility of treatments based on manipulation of inorganic phosphate homeostasis.

OBJECTIVE The prevalence of neuropathy, a common complication of diabetes, was determined in diabetic patients recruited from 109 outpatient diabetes clinics in Italy. RESEARCH DESIGN AND METHODS Neuropathy was diagnosed using the Diabetic Neuropathy Index (DNI), a standardized examination developed for use in the outpatient setting. A total of 8,757 diabetic patients were studied, 51.2% men and 48.8% women, with average and median ages of 56 and 58 years, respectively. RESULTS Of the 8,757 patients, 32.3% had neuropathy, defined as a positive score of > 2 points on the DNI. A total of 2,033 (49.6% men and 50.4% women) were administered the Diabetic Neuropathy Score (DNS), the second component of the screening program, by a neurologist. This component consists of a quantitative neurological examination and nerve conduction studies that together provide a summated score. A total of 335 patients (16.5%) were not neuropathic, and 395 (19.4%) had borderline, 453 (22.3%) mild, 592 (29.1%) moderate, and 258 (12.7%) severe neuropathy. The concordance between a positive score on the DNI and a DNS indicating neuropathy was 83.5%. The severity of neuropathy increased with both age and disease duration. Of patients with neuropathy, 64.1% had an average age between 58 and 59 years with a disease duration between 12.4 ± 8.4 years (mild neuropathy) and 15.6 ± 9.7 years (severe neuropathy). CONCLUSIONS Neuropathy is a common complication of diabetes and, in this study, was present in 32.3% of all patients. An increased awareness of the high prevalence of neuropathy can lead to early therapeutic intervention and possible prevention of later neuropathic complications, such as infection and foot ulcers.