Hirofumi Kodera

De novo mutations in the autophagy gene WDR45 cause static encephalopathy of childhood with neurodegeneration in adulthood.

Static encephalopathy of childhood with neurodegeneration in adulthood (SENDA) is a recently established subtype of neurodegeneration with brain iron accumulation (NBIA). By exome sequencing, we found de novo heterozygous mutations in WDR45 at Xp11.23 in two individuals with SENDA, and three additional WDR45 mutations were identified in three other subjects by Sanger sequencing. Using lymphoblastoid cell lines (LCLs) derived from the subjects, aberrant splicing was confirmed in two, and protein expression was observed to be severely impaired in all five. WDR45 encodes WD-repeat domain 45 (WDR45). WDR45 (also known as WIPI4) is one of the four mammalian homologs of yeast Atg18, which has an important role in autophagy. Lower autophagic activity and accumulation of aberrant early autophagic structures were demonstrated in the LCLs of the affected subjects. These findings provide direct evidence that an autophagy defect is indeed associated with a neurodegenerative disorder in humans.

Clinical spectrum of SCN2A mutations expanding to Ohtahara syndrome

Objective: We aimed to investigate the possible association between SCN2A mutations and early-onset epileptic encephalopathies (EOEEs). Methods: We recruited a total of 328 patients with EOEE, including 67 patients with Ohtahara syndrome (OS) and 150 with West syndrome. SCN2A mutations were examined using high resolution melt analysis or whole exome sequencing. Results: We found 14 novel SCN2A missense mutations in 15 patients: 9 of 67 OS cases (13.4%), 1 of 150 West syndrome cases (0.67%), and 5 of 111 with unclassified EOEEs (4.5%). Twelve of the 14 mutations were confirmed as de novo, and all mutations were absent in 212 control exomes. A de novo mosaic mutation (c.3976G>C) with a mutant allele frequency of 18% was detected in one patient. One mutation (c.634A>G) was found in transcript variant 3, which is a neonatal isoform. All 9 mutations in patients with OS were located in linker regions between 2 transmembrane segments. In 7 of the 9 patients with OS, EEG findings transitioned from suppression-burst pattern to hypsarrhythmia. All 15 of the patients with novel SCN2A missense mutations had intractable seizures; 3 of them were seizure-free at the last medical examination. All patients showed severe developmental delay. Conclusions: Our study confirmed that SCN2A mutations are an important genetic cause of OS. Given the wide clinical spectrum associated with SCN2A mutations, genetic testing for SCN2A should be considered for children with different epileptic conditions.

Clinical spectrum of early onset epileptic encephalopathies caused by KCNQ2 mutation.

KCNQ2 mutations have been found in patients with benign familial neonatal seizures, myokymia, or early onset epileptic encephalopathy (EOEE). In this study, we aimed to delineate the clinical spectrum of EOEE associated with KCNQ2 mutation.

De Novo Mutations in SLC35A2 Encoding a UDP-Galactose Transporter Cause Early-Onset Epileptic Encephalopathy

Early‐onset epileptic encephalopathies (EOEE) are severe neurological disorders characterized by frequent seizures accompanied by developmental regression or retardation. Whole‐exome sequencing of 12 patients together with five pairs of parents and subsequent Sanger sequencing in additional 328 EOEE patients identified two de novo frameshift and one missense mutations in SLC35A2 at Xp11.23, respectively. The three patients are all females. X‐inactivation analysis of blood leukocyte DNA and mRNA analysis using lymphoblastoid cells derived from two patients with a frameshift mutation indicated that only the wild‐type SLC35A2 allele was expressed in these cell types, at least in part likely as a consequence of skewed X‐inactivation. SLC35A2 encodes a UDP‐galactose transporter (UGT), which selectively supplies UDP‐galactose from the cytosol to the Golgi lumen. Transient expression experiments revealed that the missense mutant protein was correctly localized in the Golgi apparatus. In contrast, the two frameshift mutant proteins were not properly expressed, suggesting that their function is severely impaired. Defects in the UGT can cause congenital disorders of glycosylation. Of note, no abnormalities of glycosylation were observed in three serum glycoproteins, which is consistent with favorably skewed X‐inactivation. We hypothesize that a substantial number of neurons might express the mutant SLC35A2 allele and suffer from defective galactosylation, resulting in EOEE.

Targeted capture and sequencing for detection of mutations causing early onset epileptic encephalopathy.

Early onset epileptic encephalopathies (EOEEs) are heterogeneous epileptic disorders caused by various abnormalities in causative genes including point mutations and copy number variations (CNVs). In this study, we performed targeted capture and sequencing of a subset of genes to detect point mutations and CNVs simultaneously.

De novo SOX11 mutations cause Coffin–Siris syndrome

Coffin-Siris syndrome (CSS) is a congenital disorder characterized by growth deficiency, intellectual disability, microcephaly, characteristic facial features and hypoplastic nails of the fifth fingers and/or toes. We previously identified mutations in five genes encoding subunits of the BAF complex, in 55% of CSS patients. Here we perform whole-exome sequencing in additional CSS patients, identifying de novo SOX11 mutations in two patients with a mild CSS phenotype. sox11a/b knockdown in zebrafish causes brain abnormalities, potentially explaining the brain phenotype of CSS. SOX11 is the downstream transcriptional factor of the PAX6-BAF complex, highlighting the importance of the BAF complex and SOX11 transcriptional network in brain development.

GRIN1 mutations cause encephalopathy with infantile-onset epilepsy, and hyperkinetic and stereotyped movement disorders.

Recently, de novo mutations in GRIN1 have been identified in patients with nonsyndromic intellectual disability and epileptic encephalopathy. Whole exome sequencing (WES) analysis of patients with genetically unsolved epileptic encephalopathies identified four patients with GRIN1 mutations, allowing us to investigate the phenotypic spectrum of GRIN1 mutations.

De novo KCNT1 mutations in early-onset epileptic encephalopathy

KCNT1 mutations have been found in epilepsy of infancy with migrating focal seizures (EIMFS; also known as migrating partial seizures in infancy), autosomal dominant nocturnal frontal lobe epilepsy, and other types of early onset epileptic encephalopathies (EOEEs). We performed KCNT1‐targeted next‐generation sequencing (207 samples) and/or whole‐exome sequencing (229 samples) in a total of 362 patients with Ohtahara syndrome, West syndrome, EIMFS, or unclassified EOEEs. We identified nine heterozygous KCNT1 mutations in 11 patients: nine of 18 EIMFS cases (50%) in whom migrating foci were observed, one of 180 West syndrome cases (0.56%), and one of 66 unclassified EOEE cases (1.52%). KCNT1 mutations occurred de novo in 10 patients, and one was transmitted from the patients mother who carried a somatic mosaic mutation. The mutations accumulated in transmembrane segment 5 (2/9, 22.2%) and regulators of K+ conductance domains (7/9, 77.8%). Five of nine mutations were recurrent. Onset ages ranged from the neonatal period (<1 month) in five patients (5/11, 45.5%) to 1–4 months in six patients (6/11, 54.5%). A generalized attenuation of background activity on electroencephalography was seen in six patients (6/11, 54.5%). Our study demonstrates that the phenotypic spectrum of de novo KCNT1 mutations is largely restricted to EIMFS.

Mutations in COG2 encoding a subunit of the conserved oligomeric golgi complex cause a congenital disorder of glycosylation

The conserved oligomeric Golgi (COG) complex is involved in intra‐Golgi retrograde trafficking, and mutations in six of its eight subunits have been reported in congenital disorders of glycosylation (CDG). Here we report a patient showing severe acquired microcephaly, psychomotor retardation, seizures, liver dysfunction, hypocupremia, and hypoceruloplasminemia. Analysis of his serum glycoproteins revealed defects in both sialylation and galactosylation of glycan termini. Trio‐based whole‐exome sequencing identified two heterozygous mutations in COG2: a de novo frameshift mutation [c.701dup (p.Tyr234*)] and a missense mutation [c.1900T > G (p.Trp634Gly)]. Sequencing of cloned reverse‐transcription polymerase chain reaction (RT‐PCR) products revealed that both mutations were located on separate alleles, as expected, and that the mutant transcript harboring the frameshift mutation underwent degradation. The c.1900T > G (p.Trp634Gly) mutation is located in a domain highly conserved among vertebrates and was absent from both the public database and our control exomes. Protein expression of COG2, along with COG3 and COG4, was decreased in fibroblasts from the patient. Our data strongly suggest that these compound heterozygous mutations in COG2 are causative of CDG.

De novo GABRA1 mutations in Ohtahara and West syndromes

GABRA1 mutations have been identified in patients with familial juvenile myoclonic epilepsy, sporadic childhood absence epilepsy, and idiopathic familial generalized epilepsy. In addition, de novo GABRA1 mutations were recently reported in a patient with infantile spasms and four patients with Dravet syndrome. Those reports suggest that GABRA1 mutations are associated with infantile epilepsy including early onset epileptic encephalopathies. In this study, we searched for GABRA1 mutations in patients with infantile epilepsy to investigate the phenotypic spectrum of GABRA1 mutations.