Takanori Yamagata

Mutations affecting components of the SWI/SNF complex cause Coffin-Siris syndrome.

By exome sequencing, we found de novo SMARCB1 mutations in two of five individuals with typical Coffin-Siris syndrome (CSS), a rare autosomal dominant anomaly syndrome. As SMARCB1 encodes a subunit of the SWItch/Sucrose NonFermenting (SWI/SNF) complex, we screened 15 other genes encoding subunits of this complex in 23 individuals with CSS. Twenty affected individuals (87%) each had a germline mutation in one of six SWI/SNF subunit genes, including SMARCB1, SMARCA4, SMARCA2, SMARCE1, ARID1A and ARID1B.

Epidemiology of acute encephalopathy in Japan, with emphasis on the association of viruses and syndromes

A research committee supported by the Japanese government conducted a nationwide survey on the epidemiology of acute encephalopathy in Japan using a questionnaire. A total of 983 cases reportedly had acute encephalopathy during the past 3 years, 2007-2010. Among the pathogens of the preceding infection, influenza virus was the most common, followed by human herpesvirus-6 (HHV-6) and rotavirus. Among syndromes of acute encephalopathy, acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) was the most frequent, followed by clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS), acute necrotizing encephalopathy (ANE) and hemorrhagic shock and encephalopathy syndrome (HSES). Influenza virus was strongly associated with ANE and MERS, HHV-6 with AESD, and rotavirus with MERS. Mortality was high in ANE and HSES, but was low in AESD, MERS and HHV-6-associated encephalopathy. Neurologic sequelae were common in AESD and ANE, but were absent in MERS.

Dominant-Negative Mutations in α-II Spectrin Cause West Syndrome with Severe Cerebral Hypomyelination, Spastic Quadriplegia, and Developmental Delay

A de novo 9q33.3-q34.11 microdeletion involving STXBP1 has been found in one of four individuals (group A) with early-onset West syndrome, severe hypomyelination, poor visual attention, and developmental delay. Although haploinsufficiency of STXBP1 was involved in early infantile epileptic encephalopathy in a previous different cohort study (group B), no mutations of STXBP1 were found in two of the remaining three subjects of group A (one was unavailable). We assumed that another gene within the deletion might contribute to the phenotype of group A. SPTAN1 encoding alpha-II spectrin, which is essential for proper myelination in zebrafish, turned out to be deleted. In two subjects, an in-frame 3 bp deletion and a 6 bp duplication in SPTAN1 were found at the initial nucleation site of the alpha/beta spectrin heterodimer. SPTAN1 was further screened in six unrelated individuals with WS and hypomyelination, but no mutations were found. Recombinant mutant (mut) and wild-type (WT) alpha-II spectrin could assemble heterodimers with beta-II spectrin, but alpha-II (mut)/beta-II spectrin heterodimers were thermolabile compared with the alpha-II (WT)/beta-II heterodimers. Transient expression in mouse cortical neurons revealed aggregation of alpha-II (mut)/beta-II and alpha-II (mut)/beta-III spectrin heterodimers, which was also observed in lymphoblastoid cells from two subjects with in-frame mutations. Clustering of ankyrinG and voltage-gated sodium channels at axon initial segment (AIS) was disturbed in relation to the aggregates, together with an elevated action potential threshold. These findings suggest that pathological aggregation of alpha/beta spectrin heterodimers and abnormal AIS integrity resulting from SPTAN1 mutations were involved in pathogenesis of infantile epilepsy.

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.

Mutations in the gene encoding CADM1 are associated with autism spectrum disorder.

The unified idea on the molecular pathogenesis of Autism Spectrum Disorder (ASD) is still unknown although mutations in genes encoding neuroligins and SHANK3 have been shown in a small part of the patients. RA175/SynCAM1/CADM1(CADM1), a member of immunoglobulin superfamily, is another synaptic cell adhesion molecule. To clarify the idea that impaired synaptogenesis underlies the pathogenesis of ASD, we examined the relationship between mutations in the CADM1 gene and ASD. We found two missense mutations, C739A(H246N) and A755C(Y251S), in the CADM1 gene of male Caucasian ASD patients and their family members. Both mutations were located in the third immunoglobulin domain, which is essential for trans-active interaction. The mutated CADM1 exhibited less amount of high molecular weight with the matured oligosaccharide, defective trafficking to the cell surface, and more susceptibility to the cleavage and or degradation. Our findings provide key support for the unified idea that impaired synaptogenesis underlies the pathogenesis of ASD.

BAC array CGH reveals genomic aberrations in idiopathic mental retardation

Array using 2,173 BAC clones covering the whole human genome has been constructed. All clones spotted were confirmed to show a unique signal at the predicted chromosomal location by FISH analysis in our laboratory. A total of 30 individuals with idiopathic mental retardation (MR) were analyzed by comparative genomic hybridization using this array. Three deletions, one duplication, and one unbalanced translocation could be detected in five patients, which are likely to contribute to MR. The constructed array was shown to be an efficient tool for the detection of pathogenic genomic rearrangements in MR patients as well as copy number polymorphisms (CPNs).

Autism spectrum disorder is related to endoplasmic reticulum stress induced by mutations in the synaptic cell adhesion molecule, CADM1

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with an unknown molecular pathogenesis. A recent molecular focus has been the mutated neuroligin 3, neuroligin 3(R451C), in gain-of-function studies and for its role in induced impairment of synaptic function, but endoplasmic reticulum (ER) stress induced by mutated molecules also deserves investigation. We previously found two missense mutations, H246N and Y251S, in the gene-encoding synaptic cell adhesion molecule-1 (CADM1) in ASD patients, including cleavage of the mutated CADM1 and its intracellular accumulation. In this study, we found that the mutated CADM1 showed slightly reduced homophilic interactions in vitro but that most of its interactions persist. The mutated CADM1 also showed morphological abnormalities, including shorter dendrites, and impaired synaptogenesis in neurons. Wild-type CADM1 was partly localized to the ER of C2C5 cells, whereas mutated CADM1 mainly accumulated in the ER despite different sensitivities toward 4-phenyl butyric acid with chemical chaperone activity and rapamycin with promotion activity for degradation of the aggregated protein. Modeling analysis suggested a direct relationship between the mutations and the conformation alteration. Both mutated CADM1 and neuroligin 3(R451C) induced upregulation of C/EBP-homologous protein (CHOP), an ER stress marker, suggesting that in addition to the trafficking impairment, this CHOP upregulation may also be involved in ASD pathogenesis.

Elastic fiber degeneration in Costello syndrome

Clinical and pathological observations of a 6-month-old boy with Costello syndrome are reported. The main clinical findings were loose skin of the neck, hands, and feet, deep palmar and plantar creases, typical “coarse” face with thick lips and macroglossia, relative macrocephaly, mental retardation, short stature, arrhythmia, large size for gestational age, and poor feeding. At age 6 months he died of rhabdomyolysis. The major pathological findings were fine, disrupted, and loosely-constructed elastic fibers in the skin, tongue, pharynx, larynx, and upper esophagus, but not in the bronchi, alveoli, aorta, or coronary arteries. Hyperplasia of collagen fibers in the skin, hyperplasia of the mucous glands in the bronchus, narrowing of the pulmonary artery, degeneration of the atrial conduction system, calcification and ballooning of skeletal muscle fibers with infiltration of macrophages, and myoglobin depositions in the collecting ducts in the kidney were also observed. The degeneration of elastic fibers was confirmed in the skin of a second Costello syndrome patient. Expression of elastin mRNA in the patients fibroblasts was normal in size and amount. Given that elastic fiber degeneration was observed in the tissues with clinical symptoms, we speculate that a defect of elastic fibers, possibly relating to alternative splicing in the elastin gene or to defects in elastin microfibrils, might be involved in the pathogenesis of Costello syndrome.

Clinical correlations of mutations affecting six components of the SWI/SNF complex: Detailed description of 21 patients and a review of the literature

Mutations in the components of the SWItch/sucrose nonfermentable (SWI/SNF)‐like chromatin remodeling complex have recently been reported to cause Coffin–Siris syndrome (CSS), Nicolaides–Baraitser syndrome (NCBRS), and ARID1B‐related intellectual disability (ID) syndrome. We detail here the genotype‐phenotype correlations for 85 previously published and one additional patient with mutations in the SWI/SNF complex: four with SMARCB1 mutations, seven with SMARCA4 mutations, 37 with SMARCA2 mutations, one with an SMARCE1 mutation, three with ARID1A mutations, and 33 with ARID1B mutations. The mutations were associated with syndromic ID and speech impairment (severe/profound in SMARCB1, SMARCE1, and ARID1A mutations; variable in SMARCA4, SMARCA2, and ARID1B mutations), which was frequently accompanied by agenesis or hypoplasia of the corpus callosum. SMARCB1 mutations caused “classical” CSS with typical facial “coarseness” and significant digital/nail hypoplasia. SMARCA4 mutations caused CSS without typical facial coarseness and with significant digital/nail hypoplasia. SMARCA2 mutations caused NCBRS, typically with short stature, sparse hair, a thin vermillion of the upper lip, an everted lower lip and prominent finger joints. A SMARCE1 mutation caused CSS without typical facial coarseness and with significant digital/nail hypoplasia. ARID1A mutations caused the most severe CSS with severe physical complications. ARID1B mutations caused CSS without typical facial coarseness and with mild digital/nail hypoplasia, or caused syndromic ID. Because of the common underlying mechanism and overlapping clinical features, we propose that these conditions be referred to collectively as “SWI/SNF‐related ID syndromes”.

Mutation analysis of methyl-CpG binding protein family genes in autistic patients

Methyl-CpG binding protein 2 gene (MECP2), the gene implicated in Rett syndrome, was also reported to be involved in mental retardation and autism. MECP2, MBD1, MBD2, MBD3, and MBD4 comprise a nuclear protein family sharing the methyl-CpG binding domain (MBD) and are related to transcriptional repression. In 65 Japanese autistic patients, all the exons of each gene were screened for mutations by DHPLC, and the results were confirmed by direct sequencing. An R269C mutation that resulted in the addition of cysteine near a cysteine rich region was found in the MBD1 gene in one patient. This mutation was also detected in the patients father with some phenotypes of autism and his normal sister, but not in 151 controls. Two repeat length polymorphisms, (GGGGCC)2 to 3 and (GGC)4 to 5, were detected in MBD2, and several polymorphisms were detected in each gene. Although our findings could not confirm that the genes of this family are responsible for the etiology in the majority of autistic patients, the R269C mutation in the MBD1 gene may relate to autism. The potential association of the high-polymorphic gene variants with autism needs to be studied further. Furthermore, these polymorphisms are useful for linkage analysis.