Dominant mutation of CCDC78 in a unique congenital myopathy with prominent internal nuclei and atypical cores.

Congenital myopathies are clinically and genetically heterogeneous diseases that typically present in childhood with hypotonia and weakness and are most commonly defined by changes observed in muscle biopsy. Approximately 40% of congenital myopathies are currently genetically unresolved. We identified a family with dominantly inherited congenital myopathy characterized by distal weakness and biopsy changes that included core-like areas and increased internalized nuclei. To identify the causative genetic abnormality in this family, we performed linkage analysis followed by whole-exome capture and next-generation sequencing. A splice-acceptor variant in previously uncharacterized CCDC78 was detected in affected individuals and absent in unaffected family members and > 10,000 controls. This variant alters RNA-transcript processing and results in a 222 bp in-frame insertion. CCDC78 is expressed in skeletal muscle, enriched in the perinuclear region and the triad, and found in intracellular aggregates in patient muscle. Modeling of the CCDC78 mutation in zebrafish resulted in changes mirroring the human disease that included altered motor function and abnormal muscle ultrastructure. Using a combination of linkage analysis, next-generation sequencing, and modeling in the zebrafish, we have identified a CCDC78 mutation associated with a unique myopathy with prominent internal nuclei and atypical cores.

Mutations in KCND3 cause spinocerebellar ataxia type 22.

OBJECTIVE: To identify the causative gene in spinocerebellar ataxia (SCA) 22, an autosomal dominant cerebellar ataxia mapped to chromosome 1p21-q23. METHODS: We previously characterized a large Chinese family with progressive ataxia designated SCA22, which overlaps with the locus of SCA19. The disease locus in a French family and an Ashkenazi Jewish American family was also mapped to this region. Members from all 3 families were enrolled. Whole exome sequencing was performed to identify candidate mutations, which were narrowed by linkage analysis and confirmed by Sanger sequencing and cosegregation analyses. Mutational analyses were also performed in 105 Chinese and 55 Japanese families with cerebellar ataxia. Mutant gene products were examined in a heterologous expression system to address the changes in protein localization and electrophysiological functions. RESULTS: We identified heterozygous mutations in the voltage-gated potassium channel Kv4.3-encoding gene KCND3: an in-frame 3-nucleotide deletion c.679_681delTTC p.F227del in both the Chinese and French pedigrees, and a missense mutation c.1034G>T p.G345V in the Ashkenazi Jewish family. Direct sequencing of KCND3 further identified 3 mutations, c.1034G>T p.G345V, c.1013T>C p.V338E, and c.1130C>T p.T377M, in 3 Japanese kindreds. Immunofluorescence analyses revealed that the mutant p.F227del Kv4.3 subunits were retained in the cytoplasm, consistent with the lack of A-type K(+) channel conductance in whole cell patch-clamp recordings. INTERPRETATION: Our data identify the cause of SCA19/22 in patients of diverse ethnic origins as mutations in KCND3. These findings further emphasize the important role of ion channels as key regulators of neuronal excitability in the pathogenesis of cerebellar degeneration.

Homozygous splice mutation in CWF19L1 in a Turkish family with recessive ataxia syndrome.

OBJECTIVE: To elucidate the genetic cause of a rare recessive ataxia presented by 2 siblings from a consanguineous Turkish family with a nonprogressive, congenital ataxia with mental retardation of unknown etiology. METHODS: Whole-exome sequencing was combined with homozygosity mapping, linkage, and expression analysis to identify candidate genes, confirmed by Sanger sequencing. Reverse transcription-PCR and immunoblotting were used to determine the functional consequences of the gene variant. A zebrafish model was developed using morpholino-mediated knockdown. RESULTS: We identified a homozygous mutation at the invariant +1 position (c.964+1G>A) in intron 9 of the CWF19L1 (complexed with cdc5 protein 19-like 1) gene. This mutation is absent in >6,500 European and African American individuals and 200 Turkish control DNAs. The mutation causes exon skipping, reduction in messenger RNA levels, and protein loss in cell lines of affected individuals. Morpholino-mediated knockdown in a zebrafish model demonstrates that loss of the evolutionarily highly conserved CWF19L1, whose normal biological function is unknown, alters cerebellar morphology and causes movement abnormalities. CONCLUSIONS: Our results suggest that CWF19L1 mutations may be a novel cause of recessive ataxia with developmental delay. Our research may help with diagnosis, especially in Turkey, identify causes of other ataxias, and may lead to novel therapies.