BackgroundRett syndrome (RTT) is a characteristic neurological disease presenting with regressive loss of neurodevelopmental milestones. Typical RTT is generally caused by abnormality of methyl-CpG binding protein 2 (MECP2). Our objective to investigate the genetic landscape of MECP2-negative typical/atypical RTT and RTT-like phenotypes using whole exome sequencing (WES).MethodsWe performed WES on 77 MECP2-negative patients either with typical RTT (n=11), atypical RTT (n=22) or RTT-like phenotypes (n=44) incompatible with the RTT criteria.ResultsPathogenic or likely pathogenic single-nucleotide variants in 28 known genes were found in 39 of 77 (50.6%) patients. WES-based CNV analysis revealed pathogenic deletions involving six known genes (including MECP2) in 8 of 77 (10.4%) patients. Overall, diagnostic yield was 47 of 77 (61.0 %). Furthermore, strong candidate variants were found in four novel genes: a de novo variant in each of ATPase H+ transporting V0 subunit A1 (ATP6V0A1), ubiquitin-specific peptidase 8 (USP8) and microtubule-associated serine/threonine kinase 3 (MAST3), as well as biallelic variants in nuclear receptor corepressor 2 (NCOR2).ConclusionsOur study provides a new landscape including additional genetic variants contributing to RTT-like phenotypes, highlighting the importance of comprehensive genetic analysis.
Disorders of sex development (DSDs) are defined as congenital conditions in which chromosomal, gonadal or anatomical sex is atypical. In many DSD cases, genetic causes remain to be elucidated. Here, we performed a case–control exome sequencing study comparing gene-based burdens of rare damaging variants between 26 DSD cases and 2625 controls. We found exome-wide significant enrichment of rare heterozygous truncating variants in the MYRF gene encoding myelin regulatory factor, a transcription factor essential for oligodendrocyte development. All three variants occurred de novo. We identified an additional 46,XY DSD case of a de novo damaging missense variant in an independent cohort. The clinical symptoms included hypoplasia of Müllerian derivatives and ovaries in 46,XX DSD patients, defective development of Sertoli and Leydig cells in 46,XY DSD patients and congenital diaphragmatic hernia in one 46,XY DSD patient. As all of these cells and tissues are or partly consist of coelomic epithelium (CE)-derived cells (CEDC) and CEDC developed from CE via proliferaiton and migration, MYRF might be related to these processes. Consistent with this hypothesis, single-cell RNA sequencing of foetal gonads revealed high expression of MYRF in CE and CEDC. Reanalysis of public chromatin immunoprecipitation sequencing data for rat Myrf showed that genes regulating proliferation and migration were enriched among putative target genes of Myrf. These results suggested that MYRF is a novel causative gene of 46,XY and 46,XX DSD and MYRF is a transcription factor regulating CD and/or CEDC proliferation and migration, which is essential for development of multiple organs.
Although there are many known Mendelian genes linked to epileptic or developmental and epileptic encephalopathy (EE/DEE), its genetic architecture is not fully explained. Here, we address this incompleteness by analyzing exomes of 743 EE/DEE cases and 2366 controls. We observe that damaging ultra-rare variants (dURVs) unique to an individual are significantly overrepresented in EE/DEE, both in known EE/DEE genes and the other non-EE/DEE genes. Importantly, enrichment of dURVs in non-EE/DEE genes is significant, even in the subset of cases with diagnostic dURVs ( P = 0.000215), suggesting oligogenic contribution of non-EE/DEE gene dURVs. Gene-based analysis identifies exome-wide significant ( P = 2.04 × 10 −6 ) enrichment of damaging de novo mutations in NF1 , a gene primarily linked to neurofibromatosis, in infantile spasm. Together with accumulating evidence for roles of oligogenic or modifier variants in severe neurodevelopmental disorders, our results highlight genetic complexity in EE/DEE, and indicate that EE/DEE is not an aggregate of simple Mendelian disorders.
Episodic ataxias (EAs) are rare channelopathies characterized by recurrent ataxia and vertigo, having eight subtypes. Mutated genes were found in four of these eight subtypes (EA1, EA2, EA5, and EA6). To date, only four missense mutations in the Solute Carrier Family 1 Member 3 gene (SLC1A3) have been reported to cause EA6. SLC1A3 encodes excitatory amino-acid transporter 1, which is a trimeric transmembrane protein responsible for glutamate transport in the synaptic cleft. In this study, we found a novel missense mutation, c.383T>G (p.Met128Arg) in SLC1A3, in an EA patient by whole-exome sequencing. The modeled structural analysis suggested that p.Met128Arg may affect the hydrophobic transmembrane environment and protein function. Analysis of the pathogenicity of all mutations found in SLC1A3 to date using multiple prediction tools showed some advantage of using the Mendelian Clinically Applicable Pathogenicity (M-CAP) score. Various types of SLC1A3 variants, including nonsense mutations and indels, in the ExAC database suggest that the loss-of-function mechanism by SLC1A3 mutations is unlikely in EA6. The current mutation (p.Med128Arg) presumably has a gain-of-function effect as described in a previous report.
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