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Ciliopathies are clinically and genetically heterogeneous diseases. We studied three patients from two independent families presenting with features of Joubert syndrome: abnormal breathing pattern during infancy, developmental delay/intellectual disability, cerebellar ataxia, molar tooth sign on magnetic resonance imaging scans, and polydactyly. We identified biallelic loss‐of‐function (LOF) variants in CBY1, segregating with the clinical features of Joubert syndrome in the families. CBY1 localizes to the distal end of the mother centriole, contributing to the formation and function of cilia. In accordance with the clinical and mutational findings in the affected individuals, we demonstrated that depletion of Cby1 in zebrafish causes ciliopathy‐related phenotypes. Levels of CBY1 transcript were found reduced in the patients compared with controls, suggesting degradation of the mutated transcript through nonsense‐mediated messenger RNA decay. Accordingly, we could detect CBY1 protein in fibroblasts from controls, but not from patients by immunofluorescence. Furthermore, we observed reduced ability to ciliate, increased ciliary length, and reduced levels of the ciliary proteins AHI1 and ARL13B in patient fibroblasts. Our data show that CBY1 LOF‐variants cause a ciliopathy with features of Joubert syndrome.

Mitochondrial DNA depletion syndromes (MTDPS) represent a clinically and genetically heterogeneous group of autosomal recessive disorders, caused by mutations in genes involved in maintenance of mitochondrial DNA (mtDNA). Biallelic mutations in FBXL4 were recently described to cause encephalomyopathic MTDPS13. The syndrome has infantile onset and presents with hypotonia, feeding difficulties, a pattern of mild facial dysmorphisms, global developmental delay and brain atrophy. Laboratory investigations reveal elevated blood lactate levels, unspecific mitochondrial respiratory chain (MRC) enzyme deficiencies and mtDNA depletion. We report a novel missense variant, c.1442T > C (p.Leu481Pro), in FBXL4 (NM_012160.4) in a Norwegian boy with clinical, biochemical and cerebral MRI characteristics consistent with MTDPS13. The FBXL4 c.1442T > C (p.Leu481Pro) variant was not present in public databases, 149 Norwegian controls nor an in-house database containing whole exome sequencing data from 440 individuals, and it was predicted in silico to be deleterious to the protein function. Activities of MRC enzymes were normal in muscle tissue (complexes I-IV) and cultured skin fibroblasts (complexes I-V) from the patient, but mtDNA depletion was confirmed in muscle, thus supporting the predicted pathogenicity of the FBXL4 c.1442T > C (p.Leu481Pro) variant. On clinical indication of mitochondrial encephalomyopathy, sequencing of FBXL4 should be performed, even when the activity levels of the MRC enzymes are normal.

The transcription factor SOX3 is widely expressed in early vertebrate brain development. In humans, duplication of SOX3 and polyalanine expansions at its C-terminus may cause intellectual disability and hypopituitarism. Sox3 knock-out mice show a variable phenotype including structural and functional anomalies affecting the branchial arches and midline cerebral structures such as the optic chiasm and the hypothalamo-pituitary axis. SOX3 is claimed to be required in normal brain development and function in mice and humans, as well as in pituitary and craniofacial development. We report on an 8-year-old boy with a 2.1 Mb deletion in Xq27.1q27.2, which was found to be inherited from his healthy mother. To our knowledge, this is the smallest deletion including the entire SOX3 gene in a male reported to date. He is mildly intellectually disabled with language delay, dysarthria, behavior problems, minor facial anomalies, and hyperphagia. Hormone levels including growth, adrenocorticotropic and thyroid stimulating hormones are normal. Magnetic resonance imaging (MRI) at age 6 years showed no obvious brain anomalies. Genetic redundancy between the three members of the B1 subfamily of SOX proteins during early human brain development likely explains the apparently normal development of brain structures in our patient who is nullisomic for SOX3. © 2013 Wiley Periodicals, Inc.

Import of peroxisomal matrix proteins, crucial for peroxisome biogenesis, is mediated by the cytosolic receptors PEX5 and PEX7 that recognize proteins carrying peroxisomal targeting signals 1 or 2 (PTS1 or PTS2), respectively. Mutations in PEX5 or 12 other PEX genes cause peroxisome biogenesis disorders, collectively named the Zellweger spectrum disorders (ZSDs), whereas mutations in PEX7 cause rhizomelic chondrodysplasia punctata type 1 (RCDP1). Three additional RCDP types, RCDP2-3-4, are caused, respectively, by mutations in GNPAT, AGPS and FAR1, encoding enzymes involved in plasmalogen biosynthesis. Here we report a fifth type of RCDP (RCDP5) caused by a novel mutation in PEX5. In four patients with RCDP from two independent families, we identified a homozygous frame shift mutation c.722dupA (p.Val242Glyfs(∗)33) in PEX5 (GenBank: NM_001131023.1). PEX5 encodes two isoforms, PEX5L and PEX5S, and we show that the c.722dupA mutation, located in the PEX5L-specific exon 9, results in loss of PEX5L only. Both PEX5 isoforms recognize PTS1-tagged proteins, but PEX5L is also a co-receptor for PTS2-tagged proteins. Previous patients with PEX5 mutations had ZSD, mainly due to deficient import of PTS1-tagged proteins. Similarly to mutations in PEX7, loss of PEX5L results in deficient import of PTS2-tagged proteins only, thus causing RCDP instead of ZSD. We demonstrate that PEX5L expression restores the import of PTS2-tagged proteins in patient fibroblasts. Due to the biochemical overlap between RCDP1 and RCDP5, sequencing of PEX7 and exon 9 in PEX5 should be performed in patients with a selective defect in the import of PTS2-tagged proteins.

2p15p16.1-deletion syndrome was first described in 2007 based on the clinical presentation of two patients. The syndrome is characterized by intellectual disability, autism spectrum disorders, microcephaly, dysmorphic facial features and a variety of congenital organ defects. The precise genotype–phenotype correlation in 2p15-deletion syndrome is not understood. However, greater insight can be obtained by thorough clinical investigation of patients carrying deletions, especially those of small size. We report a 21-year-old male patient with features overlapping the clinical spectrum of the 2p15p16.1-deletion syndrome, such as intellectual disability, dysmorphic facial features, and congenital defects. He carried a 230 kb de novo deletion (chr2:61500346-61733075 bp, hg19), which affects the genes USP34, SNORA70B and XPO1. While there is a lack of functional data on SNORA70B, the involvement of USP34 and XPO1 in the regulation of fundamental developmental processes is well known. We suggest that haploinsufficiency of one or both of these genes is likely to be responsible for the disease in our patient.

We report a 11 year old male patient ascertained for mild intellectual disability and minor dysmorphic features, carrying a 1 Mb de novo deletion on chromosome 11q13.1q13.2 detected by aCGH. This is the first report of a deletion in this region in a patient presenting with intellectual impairment and mild dysmorphic traits. The 1 Mb deleted area encompasses 47 RefSeq genes, including Cornichon homologue 2 (CNIH2), Cofilin-1 (CFL1) and neuronal PAS domain-containing protein 4 (NPAS4), which are highly expressed in the central nervous system. Knockout of the CNIH2 and CFL1 orthologues in animals results in migration disturbances, while low or no expression of Npas4 in mice results in impairment of memory and learning. These three genes have previously been suggested as candidate genes for neurological disorders.

We report on a 11-year-old boy investigated for a clinical suspicion of Angelman syndrome (AS) (OMIM 105830) who was found to carry a de novo interstitial deletion of chromosome 15q13.2q13.3. The deletion overlaps the critical region for the newly recognized recurrent 15q13.3 deletion syndrome. This is the first report of a patient with 15q13.3 deletion syndrome with clinical features similar to that of AS, thus broadening the phenotypic spectrum associated with the 15q13.3 microdeletion syndrome.

We report of a spinocerebellar ataxia (SCA)27 in a daughter and her mother whose karyotype is 46, XX t(5;13)(q31.2;q33.1). The translocation breakpoint is identical in both patients, disrupting the gene-encoding fibroblast growth factor 14 isoform b (FGF14-1b). Clinically, both show signs of SCA, although the daughter is the most affected with early onset cerebellar ataxia, microcephaly, and severe mental retardation. FGF14-1b is the predominant isoform in brain, where it interacts with the voltage gated Na channel. Fgf14(-/-) mice develop ataxia and paroxysmal dyskinesia and have cognitive deficits. One missense and one non-sense mutation in FGF14 have previously been linked to SCA27. Truncation of one allele in our patients suggests that haploinsuffiency of FGF14 can cause SCA27.

Background Nineteen patients with deletions in chromosome 6p22-p24 have been published so far. The syndromic phenotype is varied, and includes intellectual disability, behavioural abnormalities, dysmorphic features and structural organ defects. Heterogeneous deletion breakpoints and sizes (1–17 Mb) and overlapping phenotypes have made the identification of the disease causing genes challenging. We suggest JARID2 and ATXN1, both harbored in 6p22.3, as disease causing genes. Methods and results We describe five unrelated patients with de novo deletions (0.1-4.8 Mb in size) in chromosome 6p22.3-p24.1 detected by aCGH in a cohort of approximately 3600 patients ascertained for neurodevelopmental disorders. Two patients (Patients 4 and 5) carried non-overlapping deletions that were encompassed by the deletions of the remaining three patients (Patients 1–3), indicating the existence of two distinct dosage sensitive genes responsible for impaired cognitive function in 6p22.3 deletion-patients. The smallest region of overlap (SRO I) in Patients 1–4 (189 kb) included the genes JARID2 and DTNBP1, while SRO II in Patients 1–3 and 5 (116 kb) contained GMPR and ATXN1. Patients with deletion of SRO I manifested variable degrees of cognitive impairment, gait disturbance and distinct, similar facial dysmorphic features (prominent supraorbital ridges, deep set eyes, dark infraorbital circles and midface hypoplasia) that might be ascribed to the haploinsufficiency of JARID2. Patients with deletion of SRO II showed intellectual disability and behavioural abnormalities, likely to be caused by the deletion of ATXN1. Patients 1–3 presented with lower cognitive function than Patients 4 and 5, possibly due to the concomitant haploinsufficiency of both ATXN1 and JARID2. The chromatin modifier genes ATXN1 and JARID2 are likely candidates contributing to the clinical phenotype in 6p22-p24 deletion-patients. Both genes exert their effect on the Notch signalling pathway, which plays an important role in several developmental processes. Conclusions Patients carrying JARID2 deletion manifested with cognitive impairment, gait disturbance and a characteristic facial appearance, whereas patients with deletion of ATXN1 seemed to be characterized by intellectual disability and behavioural abnormalities. Due to the characteristic facial appearance, JARID2 haploinsufficiency might represent a clinically recognizable neurodevelopmental syndrome.

Biallelic mutations in IGHMBP2 cause spinal muscular atrophy with respiratory distress type 1 (SMARD1) or Charcot–Marie–Tooth type 2S (CMT2S). We report three families variably affected by IGHMBP2 mutations. Patient 1, an 8-year-old boy with two homozygous variants: c.2T>C and c.861C>G, was wheelchair bound due to sensorimotor axonal neuropathy and chronic respiratory failure. Patient 2 and his younger sister, Patient 3, had compound heterozygous variants: c.983_987delAAGAA and c.1478C>T. However, clinical phenotypes differed markedly as the elder with sensorimotor axonal neuropathy had still unaffected respiratory function at 4.5 years, whereas the younger presented as infantile spinal muscular atrophy and died from relentless respiratory failure at 11 months. Patient 4, a 6-year-old girl homozygous for IGHMBP2 c.449+1G>T documented to result in two aberrant transcripts, was wheelchair dependent due to axonal polyneuropathy. The clinical presentation in Patients 1 and 3 were consistent with SMARD1, whereas Patients 2 and 4 were in agreement with CMT2S.