No abstract

Epileptic encephalopathies represent a clinically and genetically heterogeneous group of disorders, majority of which are of unknown etiology. We used whole-exome sequencing of a parent-offspring trio to identify the cause of early infantile epileptic encephalopathy in a boy with neonatal seizures, movement disorders, and multiple congenital anomalies who died at the age of 17 months because of respiratory illness and identified a de novo heterozygous missense mutation (c.3979A>G; p.Ile1327Val) in SCN8A (voltage-gated sodium-channel type VIII alpha subunit) gene. The variant was confirmed in the proband with Sanger sequencing. Because the clinical phenotype associated with SCN8A mutations has previously been identified only in a few patients with or without epileptic seizures, these data together with our results suggest that mutations in SCN8A can lead to early infantile epileptic encephalopathy with a broad phenotypic spectrum. Additional investigations will be worthwhile to determine the prevalence and contribution of SCN8A mutations to epileptic encephalopathies.

The CACNA1A gene encodes the transmembrane pore-forming alpha-1A subunit of the Cav 2.1 P/Q-type voltage-gated calcium channel. Several heterozygous mutations within this gene, including nonsense mutations, missense mutations, and expansion of cytosine-adenine-guanine repeats, are known to cause three allelic autosomal dominant conditions-episodic ataxia type 2, familial hemiplegic migraine type 1, and spinocerebellar ataxia type 6. An association with epilepsy and CACNA1A mutations has also been described. However, the link with epileptic encephalopathies has emerged only recently. Here we describe two patients, sister and brother, with compound heterozygous mutations in CACNA1A. Exome sequencing detected biallelic mutations in CACNA1A: A missense mutation c.4315T>A (p.Trp1439Arg) in exon 27, and a seven base pair deletion c.472_478delGCCTTCC (p.Ala158Thrfs*6) in exon 3. Both patients were normal at birth, but developed daily recurrent seizures in early infancy with concomitant extreme muscular hypotonia, hypokinesia, and global developmental delay. The brain MRI images showed progressive cerebral, cerebellar, and optic nerve atrophy. At the age of 5, both patients were blind and bedridden with a profound developmental delay. The elder sister died at that age. Their parents and two siblings were heterozygotes for one of those pathogenic mutations and expressed a milder phenotype. Both of them have intellectual disability and in addition the mother has adult onset cerebellar ataxia with a slowly progressive cerebellar atrophy. Compound heterozygous mutations in the CACNA1A gene presumably cause early onset epileptic encephalopathy, and progressive cerebral, cerebellar and optic nerve atrophy with reduced lifespan. © 2016 Wiley Periodicals, Inc.

Germline pathogenic variants in chromatin-modifying enzymes are a common cause of pediatric developmental disorders. These enzymes catalyze reactions that regulate epigenetic inheritance via histone post-translational modifications and DNA methylation. Cytosine methylation (5-methylcytosine [5mC]) of DNA is the quintessential epigenetic mark, yet no human Mendelian disorder of DNA demethylation has yet been delineated. Here, we describe in detail a Mendelian disorder caused by the disruption of DNA demethylation. TET3 is a methylcytosine dioxygenase that initiates DNA demethylation during early zygote formation, embryogenesis, and neuronal differentiation and is intolerant to haploinsufficiency in mice and humans. We identify and characterize 11 cases of human TET3 deficiency in eight families with the common phenotypic features of intellectual disability and/or global developmental delay; hypotonia; autistic traits; movement disorders; growth abnormalities; and facial dysmorphism. Mono-allelic frameshift and nonsense variants in TET3 occur throughout the coding region. Mono-allelic and bi-allelic missense variants localize to conserved residues; all but one such variant occur within the catalytic domain, and most display hypomorphic function in an assay of catalytic activity. TET3 deficiency and other Mendelian disorders of the epigenetic machinery show substantial phenotypic overlap, including features of intellectual disability and abnormal growth, underscoring shared disease mechanisms.Post-translational modifications of histone tails and DNA methylation play essential roles in development by regulating chromatin structure and gene expression. Inherited conditions that disrupt these processes-chromatin-modifying disorders or Mendelian disorders of the epigenetic machinery-account for a substantial percentage of neurodevelopmental and growth abnormalities in children. 1,2 Most known disorders in this class are caused by pathogenic variants in either histonemodifying enzymes or chromatin remodelers. Far fewer have been linked to deficiencies in the DNA methylation machinery. [3][4][5] The latter include disorders caused by de-fects in DNA methylation ''writers,'' or DNA methyltransferases (DNMTs). For example, immunodeficiencycentromeric instability-facial anomalies syndrome 1 (ICF syndrome) results from bi-allelic variants in DNMT3B (MIM: 242860). Tatton-Brown-Rahman syndrome results from mono-allelic variants in DNMT3A (MIM: 615879). Defects in ''reader'' proteins that bind to DNA methylation lead to disorders including Rett syndrome, which is caused by variants in MECP2 (MIM: 312750). [3][4][5] No Mendelian disorder has been consistently linked to the multi-step and tightly regulated process that removes DNA methylation.

Purpose: A few de novo missense variants in the cytoplasmic FMRP-interacting protein 2 (CYFIP2) gene have recently been described as a novel cause of severe intellectual disability, seizures, and hypotonia in 18 individuals, with p.Arg87 substitutions in the majority. Methods: We assembled data from 19 newly identified and all 18 previously published individuals with CYFIP2 variants. By structural modeling and investigation of WAVE-regulatory complex (WRC)-mediated actin polymerization in six patient fibroblast lines we assessed the impact of CYFIP2 variants on the WRC. Results: Sixteen of 19 individuals harbor two previously described and 11 novel (likely) disease-associated missense variants. We report p.Asp724 as second mutational hotspot (4/19 cases). Genotype-phenotype correlation confirms a consistently severe phenotype in p.Arg87 patients but a more variable phenotype in p. Asp724 and other substitutions. Three individuals with milder phenotypes carry putative loss-of-function variants, which remain of unclear pathogenicity. Structural modeling predicted missense variants to disturb interactions within the WRC or impair CYFIP2 stability. Consistent with its role in WRC-mediated actin polymerization we substantiate aberrant regulation of the actin cytoskeleton in patient fibroblasts. Conclusion: Our study expands the clinical and molecular spectrum of CYFIP2-related neurodevelopmental disorder and provides evidence for aberrant WRC-mediated actin dynamics as contributing cellular pathomechanism.

No abstract

Recently, a novel autosomal recessive developmental delay-macrocephaly syndrome was described caused by homozygous or compound heterozygous mutations in the KPTN gene. All reported patients belonged to one large Amish kindred. We report on the second case of KPTN-related syndrome in two Estonian adult sibs. The brother and sister both have macrocephaly and moderate intellectual disability, and their verbal abilities are more affected than motor development. No notable minor anomalies are present. Behavioral problems and a few episodes of seizures were reported in the brother. Whole exome sequencing carried out from the brother's DNA sample identified homozygous one-nucleotide frameshift duplication c.665dupA (p.Q222fs) in the KPTN gene. Homozygosity of both affected sibs and heterozygosity of parents were confirmed by Sanger sequencing. Thus, we confirm the pathogenicity of KPTN mutations and further delineate the novel developmental delay-macrocephaly syndrome. We also support the hypothesis that KPTN-related syndrome is not restricted to the Amish population.

Background In addition to whole exomes, large gene panels of clinically associated genes are used as high‐throughput sequencing tests in many clinical centers, but their clinical utility has been much less investigated. Materials and Methods Here we report the results of the 501 first unselected cases for whom TruSight One panel (Illumina Inc., San Diego, California) was sequenced as a clinical diagnostic test for a variety of indications in our department. The analysis was restricted to virtual subpanels based on referral forms, where doctors were asked to list candidate genes or select one from predefined larger panels. Results A probable or definite pathogenic finding was reported in 26.3% of cases. In 238 samples for whom 1 to 9 genes were requested for analysis, the diagnostic yield was significantly higher compared to other 263 cases for whom larger subpanels were requested (31.5% vs 21.7%, respectively, P = .016). Detected mutations included single nucleotide variants, small insertions and deletions, and larger copy number variants. Out of 157 reported mutations, 67 were previously undescribed. Conclusion The clinical utility of large gene panel sequencing in the context of other genetic diagnostic tests is discussed in detail.