Xiru Wu

Association between genetic variation of CACNA1H and childhood absence epilepsy

Direct sequencing of exons 3 to 35 and the exon–intron boundaries of the CACNA1H gene was conducted in 118 childhood absence epilepsy patients of Han ethnicity recruited from North China. Sixty‐eight variations have been detected in the CACNA1H gene, and, among the variations identified, 12 were missense mutations and only found in 14 of the 118 patients in a heterozygous state, but not in any of 230 unrelated controls. The identified missense mutations occurred in the highly conserved residues of the T‐type calcium channel gene. Our results suggest that CACNA1H might be an important susceptibility gene involved in the pathogenesis of childhood absence epilepsy. Ann Neurol 2003

Submicroscopic subtelomeric aberrations in Chinese patients with unexplained developmental delay/mental retardation

BackgroundSubtelomeric imbalance is widely accepted as related to developmental delay/mental retardation (DD/MR). Fine mapping of aberrations in gene-enriched subtelomeric regions provides essential clues for localizing critical regions, and provides a strategy for identifying new candidate genes. To date, no large-scale study has been conducted on subtelomeric aberrations in DD/MR patients in mainland China.MethodsThis study included 451 Chinese children with moderate to severe clinically unexplained DD/MR. The subtelomere-MLPA (multiplex ligation dependent probe amplification) and Affymetrix human SNP array 6.0 were used to determine the subtelomeric copy number variations. The exact size and the breakpoint of each identified aberration were well defined.ResultsThe submicroscopic subtelomeric aberrations were identified in 23 patients, with a detection rate of 5.1%. 16 patients had simple deletions, 2 had simple duplications and 5 with both deletions and duplications. The deletions involved 14 different subtelomeric regions (1p, 2p, 4p, 6p, 7p, 7q, 8p, 9p, 10p, 11q, 14q, 15q, 16p and 22q), and duplications involved 7 subtelomeric regions (3q, 4p, 6q, 7p, 8p, 12p and 22q). Of all the subtelomeric aberrations found in Chinese subjects, the most common was 4p16.3 deletion. The sizes of the deletions varied from 0.6 Mb to 12 Mb, with 5-143 genes inside. Duplicated regions were 0.26 Mb to 11 Mb, with 6-202 genes inside. In this study, four deleted subtelomeric regions and one duplicated region were smaller than any other previously reported, specifically the deletions in 11q25, 8p23.3, 7q36.3, 14q32.33, and the duplication in 22q13. Candidate genes inside each region were proposed.ConclusionsSubmicroscopic subtelomeric aberrations were detected in 5.1% of Chinese children with clinically unexplained DD/MR. Four deleted subtelomeric regions and one duplicated region found in this study were smaller than any previously reported, which will be helpful for further defining the candidate dosage sensitive gene associated with DD/MR.

New variants in the CACNA1H gene identified in childhood absence epilepsy.

Childhood absence epilepsy (CAE) is a common form of idiopathic generalized epilepsy with polygenic inheritance. In our previous studies, relatively high frequent variants in the T-type calcium channel gene, CACNA1H, were identified in the Chinese Han population, most of which are located in exons 6-12. The goal of this study was to identify additional variants in this region of the CACNA1H gene. To this end, exons 6-12 were sequenced in 100 newly recruited CAE trios and 191 normal controls. Thirty-nine variants were identified in CAE trios or controls, 14 of which were found only in CAE patients, including two nonsynonymous variants that were newly found. Thirteen of the 39 variants were found in both CAE patients and controls, 11 were found only in parents of CAE trios, and one was found only in controls. Twenty-eight of these variants had not been previously reported. Both permutation test and transmission/disequilibrium test (TDT) indicated that a SNP-52037C>T in intron11 was significant in association with CAE. In conclusion, these data further support the hypothesis that CACNA1H is an important susceptibility gene for CAE in the Chinese Han population.

SCN1A, SCN1B, and GABRG2 gene mutation analysis in Chinese families with generalized epilepsy with febrile seizures plus.

AbstractGeneralized epilepsy with febrile seizures plus (GEFS+; MIM#604233) is a familial epilepsy syndrome characterized by phenotypic and genetic heterogeneity. It was associated with mutations in the neuronal voltage-gated sodium channel subunit gene (SCN1A, SCN2A, SCN1B) and ligand-gated gamma aminobutyric acid receptors genes (GABRG2, GABRD). We investigated the roles of SCN1A, SCN1B, and GABRG2 mutations in the etiology of Chinese GEFS+ families. Genomic deoxyribonucleic acid (DNA) was extracted from peripheral blood lymphocytes of 23 probands and their family members. The sequences of SCN1A, SCN1B, and GABRG2 genes were analyzed by polymerase chain reaction (PCR) and direct sequencing. The major phenotypes of affected members in the 23 GEFS+ families exhibited FS and FS+, whereas rare phenotypes afebrile generalized tonic-clonic seizures (AGTCS), myoclonic-astatic epilepsy (MAE), and partial seizures were also observed. A novel SCN1A mutation, p.N935H, was identified in one family and another novel mutation in GABRG2, p.W390X, in another family. However, no SCN1B mutation was identified. The combined frequency of SCN1A, SCN1B, and GABRG2 mutations was 8.7% (2/23), extending the distribution of SCN1A and GABRG2 mutations to Chinese GEFS+ families. There were still unidentified genes contributing to the pathogenesis of GEFS+.

Amplicon Resequencing Identified Parental Mosaicism for Approximately 10% of “de novo” SCN1A Mutations in Children with Dravet Syndrome

The majority of children with Dravet syndrome (DS) are caused by de novo SCN1A mutations. To investigate the origin of the mutations, we developed and applied a new method that combined deep amplicon resequencing with a Bayesian model to detect and quantify allelic fractions with improved sensitivity. Of 174 SCN1A mutations in DS probands which were considered “de novo” by Sanger sequencing, we identified 15 cases (8.6%) of parental mosaicism. We identified another five cases of parental mosaicism that were also detectable by Sanger sequencing. Fraction of mutant alleles in the 20 cases of parental mosaicism ranged from 1.1% to 32.6%. Thirteen (65% of 20) mutations originated paternally and seven (35% of 20) maternally. Twelve (60% of 20) mosaic parents did not have any epileptic symptoms. Their mutant allelic fractions were significantly lower than those in mosaic parents with epileptic symptoms (P = 0.016). We identified mosaicism with varied allelic fractions in blood, saliva, urine, hair follicle, oral epithelium, and semen, demonstrating that postzygotic mutations could affect multiple somatic cells as well as germ cells. Our results suggest that more sensitive tools for detecting low‐level mosaicism in parents of families with seemingly “de novo” mutations will allow for better informed genetic counseling.

MECP2 and CDKL5 gene mutation analysis in Chinese patients with Rett syndrome

AbstractRett syndrome (RTT) is a progressive neurodevelopmental disorder that is caused by mutations in the X-linked methyl-CpG-binding protein2 (MECP2) gene. In this study, the MECP2 sequences in 121 unrelated Chinese patients with classical or atypical RTT were screened for deletions and mutations. In all, we identified 45 different MECP2 mutations in 102 of these RTT patients. The p. T158M mutation (15.7%) was the most common, followed in order of frequency by p. R168X (11.8%), p. R133C (6.9%), p. R270X (6.9%), p. G269fs (6.9%), p. R255X (4.9%), and p. R306C (3.9%). In addition, we identified five novel MECP2 mutations: three missense (p. K305E, p. V122M, p. A358T), one insertion (c.45-46insGGAGGA), and one 22 bp deletion (c.881-902del22). Large deletions represented 10.5% of all identified MECP2 mutations. Conversely, mutations in exon 1 appeared to be rare (0.9%). The remaining cases without MECP2 mutations were screened for the cyclin-dependent kinase-like 5 (CDKL5) gene using denaturing high-performance liquid chromatography (DHPLC). One synonymous mutation (p. I72I) was found in exon 5, suggesting that CDKL5 is a rare cause of RTT. The overall MECP2 mutation detection rate for this patient series was 84.3:87.9% in 107 classical RTT cases and 57.1% in 14 atypical RTT cases. Moreover, there were two patients with homozygous mutations and normal female karyotypes. However, we did not pinpoint a significant relationship between genotype and phenotype in these cases.

Clinical study and PLA2G6 mutation screening analysis in Chinese patients with infantile neuroaxonal dystrophy

Background and purpose:  Infantile neuroaxonal dystrophy (INAD) is a rare autosomal recessive neurodegenerative disorder. The most typical neuropathological finding of this disease is axonal swelling. Before the identification of associated mutations in PLA2G6‐encoding iPLA2‐VIA (cytosolic Ca2+‐independent phospholipids A2, group VIA) in 2006, neuropathological evidence was critical for definitive diagnosis. Only five genetic studies in INAD patients have been published worldwide, wherein 44 mutations were reported. To define the clinical and genetic characteristics of Chinese patients with INAD, 10 cases were analyzed.

SCN8A mutations in Chinese children with early onset epilepsy and intellectual disability.

Mutations in SCN8A, a voltage‐gated sodium‐channel type VIII alpha subunit gene, have recently been recognized as one of the pathogenic mechanisms leading to epilepsy and intellectual/developmental disabilities (IDDs). The aim of this study was to detect SCN8A mutations in Chinese patients with epilepsy of unknown etiology and ID/DD.

T-type calcium channel gene alpha (1G) is not associated with childhood absence epilepsy in the Chinese Han population.

We investigated whether the T-type calcium channel gene alpha (1G) is associated with childhood absence epilepsy (CAE), a form of idiopathic generalized epilepsy. We carried out direct sequencing of exons 1-37 and the exon-intron boundaries of the alpha (1G) gene in 48 Han Chinese patients with CAE and 48 normal controls. We found no mutation in the exons of alpha (1G). However, we did identify six single nucleotide polymorphisms (SNPs). Using two of these as markers, we carried out a case-control study in 192 patients with CAE and 192 normal controls. The allele and genotype distributions of all the SNPs studied were not significantly different between cases and control groups, thus the alpha (1G) gene is not an important susceptibility gene for CAE, at least in the Chinese population.

Common Polymorphisms in the CACNA1H Gene Associated with Childhood Absence Epilepsy in Chinese Han Population

Variants with a relatively high frequency in the CACNA1H gene have previously been identified in cases of childhood absence epilepsy (CAE) in the Chinese Han population most of which are located in exons 6 to 12. In present study we attempted to further investigate whether the CACNA1H gene is associated with CAE. Exons 6 to 12 of CACNA1H gene were sequenced in samples of 100 CAE trios recruited consecutively, and 191 normal human controls. Single nucleotide polymorphisms (SNPs) were studied in both single locus and haplotype analyses in 218 CAE trios, of which 118 trios were selected from our previous research. Case‐control comparisons and the transmission disequilibrium test (TDT) both supported a coding SNP (cSNP) rs9934839 (R603R) in exon 9 as being close related to CAE. The carriers of the G allele of rs9934839 had a 3‐fold higher risk of CAE than non‐carriers. Moreover, another cSNP rs8044363 was predicted to be connected directly with CAE in a Bayesian network. In addition, two haplotypes consisting of five cSNPs in the region of CACNA1H were statistically associated with CAE. Our research provides new evidence to further support the hypothesis that CACNA1H may be an important susceptibility gene for CAE in the Chinese Han population.