Fumiaki Kamada

A genome-wide association study identifies RNF213 as the first Moyamoya disease gene.

Moyamoya disease (MMD) shows progressive cerebral angiopathy characterized by bilateral internal carotid artery stenosis and abnormal collateral vessels. Although ∼15% of MMD cases are familial, the MMD gene(s) remain unknown. A genome-wide association study of 785 720 single-nucleotide polymorphisms (SNPs) was performed, comparing 72 Japanese MMD patients with 45 Japanese controls and resulting in a strong association of chromosome 17q25-ter with MMD risk. This result was further confirmed by a locus-specific association study using 335 SNPs in the 17q25-ter region. A single haplotype consisting of seven SNPs at the RNF213 locus was tightly associated with MMD (P=5.3 × 10−10). RNF213 encodes a really interesting new gene finger protein with an AAA ATPase domain and is abundantly expressed in spleen and leukocytes. An RNA in situ hybridization analysis of mouse tissues indicated that mature lymphocytes express higher levels of Rnf213 mRNA than their immature counterparts. Mutational analysis of RNF213 revealed a founder mutation, p.R4859K, in 95% of MMD families, 73% of non-familial MMD cases and 1.4% of controls; this mutation greatly increases the risk of MMD (P=1.2 × 10−43, odds ratio=190.8, 95% confidence interval=71.7–507.9). Three additional missense mutations were identified in the p.R4859K-negative patients. These results indicate that RNF213 is the first identified susceptibility gene for MMD.

Variations in the C3, C3a receptor, and C5 genes affect susceptibility to bronchial asthma

Bronchial asthma (BA) is a common chronic inflammatory disease characterized by hyperresponsive airways, excess mucus production, eosinophil activation, and the production of IgE. The complement system plays an immunoregulatory role at the interface of innate and acquired immunities. Recent studies have provided evidence that C3, C3a receptor, and C5 are linked to airway hyperresponsiveness. To determine whether genetic variations in the genes of the complement system affect susceptibility to BA, we screened single nucleotide polymorphisms (SNPs) in C3, C5, the C3a receptor gene (C3AR1), and the C5a receptor gene (C5R1) and performed association studies in the Japanese population. The results of this SNP case-control study suggested an association between 4896C/T in the C3 gene and atopic childhood BA (P=0.0078) as well as adult BA (P=0.010). When patient data were stratified according to elevated total IgE levels, 4896C/T was more closely associated with adult BA (P=0.0016). A patient-only association study suggested that severity of childhood BA was associated with 1526G/A of the C3AR1 gene (P=0.0057). We identified a high-risk haplotype of the C3 gene for childhood (P=0.0021) and adult BA (P=0.0058) and a low-risk haplotype for adult BA (P=0.00011). We also identified a haplotype of the C5 gene that was protective against childhood BA (P=1.4×10−6) and adult BA (P=0.00063). These results suggest that the C3 and C5 pathways of the complement system play important roles in the pathogenesis of BA and that polymorphisms of these genes affect susceptibility to BA.

Genomic deletion within GLDC is a major cause of non-ketotic hyperglycinaemia

Background: Non-ketotic hyperglycinaemia (NKH) is an inborn error of metabolism characterised by accumulation of glycine in body fluids and various neurological symptoms. NKH is caused by deficiency of the glycine cleavage multienzyme system with three specific components encoded by GLDC, AMT and GCSH. Most patients are deficient of the enzymatic activity of glycine decarboxylase, which is encoded by GLDC. Our recent study has suggested that there are a considerable number of GLDC mutations which are not identified by the standard exon-sequencing method. Methods: A screening system for GLDC deletions by multiplex ligation-dependent probe amplification (MLPA) has been developed. Two distinct cohorts of patients with typical NKH were screened by this method: the first cohort consisted of 45 families with no identified AMT or GCSH mutations, and the second cohort was comprised of 20 patients from the UK who were not prescreened for AMT mutations. Results:GLDC deletions were identified in 16 of 90 alleles (18%) in the first cohort and in 9 of 40 alleles (22.5%) in the second cohort. 14 different types of deletions of various lengths were identified, including one allele where all 25 exons were missing. Flanking sequences of interstitial deletions in five patients were determined, and Alu-mediated recombination was identified in three of five patients. Conclusions:GLDC deletions are a significant cause of NKH, and the MLPA analysis is a valuable first-line screening for NKH genetic testing.

The GSTP1 Gene Is a Susceptibility Gene for Childhood Asthma and the GSTM1 Gene Is a Modifier of the GSTP1 Gene

Background: Bronchial asthma is a chronic airway disorder characterized by bronchial inflammation. Oxidative stress is a key component of inflammation. Glutathione S-transferase P1 (GSTP1), the abundant isoform of glutathione S-transferases (GSTs) in lung epithelium, plays a key role in cellular protection against oxidative stress. Several studies have shown that the GSTP1 geneis involved in the pathogenesis of asthma and a gene-gene interaction may occur within the GST gene superfamily. Methods: We screened single-nucleotide polymorphisms (SNPs) at the GSTP1 locus and performed an association study in the Japanese population using two independent case-control groups (group 1: 391 pediatric patients with asthma, 462 adult patients with asthma, and 639 controls, and group 2: 115 pediatric patients with asthma and 184 controls). The effect of GSTM1 null/present genotype on the association between GSTP1 Ile105Val and asthma was also investigated. Results: We identified 20 SNPs at this locus and found this region consisted of one linkage disequilibrium block represented by four SNPs (tag SNPs). The association between the Ile105Val polymorphism in the GSTP1 gene and childhood asthma was significant in both groups (p = 0.047 in group 1, and p = 0.021 in group 2). This association was only significant in patients with GSTM1-positive genotype in both groups (group 1: GSTM1 present p = 0.013 and GSTM1 null p = 0.925, and group 2: GSTM1 present p = 0.015 and GSTM1 null p = 0.362). Conclusions: These findings suggest that the GSTP1 gene is a childhood asthma susceptible gene, and the GSTM1 gene is a modifier gene of GSTP1 for the risk of childhood asthma in the Japanese population.

Linkage and association of childhood asthma with the chromosome 12 genes.

AbstractSeveral studies have shown linkage of chromosome region 12q13-24 to bronchial asthma and related phenotypes in ethnically diverse populations. In the Japanese population, a genome-wide study failed to show strong evidence of linkage of this region. Chromosome 12 genes that showed association with the disease in at least one report include: the signal transducer and activator of transcription 6 gene (STAT6), the nitrogen oxide synthetase 1 gene (NOS1), the interferon γ gene (IFNG), and the activation-induced cytidine deaminase gene (AICDA). To evaluate the linkage between chromosome 12 and childhood asthma in the Japanese population, we performed sib-pair linkage analysis on childhood asthma families using 18 microsatellite markers on chromosome 12. To investigate association between chromosome 12 candidate genes and asthma, distributions of alleles and genotypes of repeat polymorphisms of STAT6, NOS1, and IFNG were compared between controls and patients. Single nucleotide polymorphism of AICDA was also investigated. Chromosome region 12q24.23-q24.33 showed suggestive linkage to asthma. The NOS1 intron 2 GT repeat and STAT6 exon 1 GT repeat were associated with asthma. Neither the IFNG intron 1 CA repeat nor 465C/T of AICDA showed any association with asthma. Our results suggest that NOS1 and STAT6 are asthma-susceptibility genes and that chromosome region 12q24.23-q24.33 contains other susceptibility gene(s).

A novel KCNQ4 one-base deletion in a large pedigree with hearing loss: implication for the genotype–phenotype correlation

AbstractAutosomal-dominant, nonsyndromic hearing impairment is clinically and genetically heterogeneous. We encountered a large Japanese pedigree in which nonsyndromic hearing loss was inherited in an autosomal-dominant fashion. A genome-wide linkage study indicated linkage to the DFNA2 locus on chromosome 1p34. Mutational analysis of KCNQ4 encoding a potassium channel revealed a novel one-base deletion in exon 1, c.211delC, which generated a profoundly truncated protein without transmembrane domains (p.Q71fsX138). Previously, six missense mutations and one 13-base deletion, c.211_223del, had been reported in KCNQ4. Patients with the KCNQ4 missense mutations had younger-onset and more profound hearing loss than patients with the 211_223del mutation. In our current study, 12 individuals with the c.211delC mutation manifested late-onset and pure high-frequency hearing loss. Our results support the genotype-phenotype correlation that the KCNQ4 deletions are associated with later-onset and milder hearing impairment than the missense mutations. The phenotypic difference may be caused by the difference in pathogenic mechanisms: haploinsufficiency in deletions and dominant-negative effect in missense mutations.

Development of enzyme-linked immunosorbent assays for urinary thiazide-sensitive Na-Cl cotransporter measurement

The Na-Cl cotransporter (NCC) in the distal convoluted tubules in kidney is known to be excreted in urine. However, its clinical significance has not been established because of the lack of quantitative data on urinary NCC. We developed highly sensitive enzyme-linked immunosorbent assays (ELISAs) for urinary total NCC (tNCC) and its active form, phosphorylated NCC (pNCC). We first measured the excretion of tNCC and pT55-NCC in urinary exosomes in pseudohypoaldosteronism type II (PHAII) patients since PHAII is caused by NCC activation. Highly increased excretion of tNCC and pNCC was observed in PHAII patients. In contrast, the levels of tNCC and pNCC in the urine of patients with Gitelmans syndrome were not detectable or very low, indicating that both assays could specifically detect the changes in urinary NCC excretion caused by the changes of NCC activity in the kidney. Then, to test whether these assays could be feasible for a more general patient population, we measured tNCC and pNCC in the urine of outpatients with different clinical backgrounds. Although urinary protein levels >30 mg/dl interfered with our ELISA, we could measure urinary pNCC in all patients without proteinuria. Thus we established highly sensitive and quantitative assays for urinary NCC, which could be valuable tools for estimating NCC activity in vivo.

A loss-of-function mutation in the FTSJ1 gene causes nonsyndromic X-linked mental retardation in a Japanese family.

Mental retardation (MR) is a common trait, affecting ∼2–3% of individuals in the general population. Although the etiology of MR remains largely unknown, genetics apparently play a major role. Recent molecular studies of X‐linked form of MR in European and North American countries have revealed 24 nonsyndromic X‐linked mental retardation (NS‐XLMR) genes including FTSJ1, a human homolog of the Escherichia coli 2′‐O‐rRNA methyltransferase FtsJ/RrmJ gene. Here we identified a novel FTSJ1 mutation in an XLMR family through mutation screening of a cohort of 73 unrelated Japanese male probands with MR. Sequence analysis of the proband and his mother revealed a G > A substitution at the consensus for the donor splicing site in intron 8 (c.571 + 1G > A) of FTSJ1. This mutation prevented the removal intron 8 from the pre‐mRNA, thereby leading to a frameshift in the mutant FTSJ1 mRNA and resulting in a premature termination in exon 9. Quantitative RT‐PCR showed a significant reduction of mutant FTSJ1 mRNA in the patients lymphoblast cells, which was restored by treatment with cycloheximide, a potent inhibitor of nonsense‐mediated mRNA decay (NMD). Therefore, mRNAs carrying this mutation are likely subject to degradation by NMD. Together, loss‐of‐function of FTSJ1 may be a mechanism for the cognitive dysfunction observed in this family. Our study also suggested that the FTSJ1 mutation probably accounts for XLMR in Japanese at a similar frequency (1–2%) as in Europeans.

Rapid diagnosis of glycine encephalopathy by 13C-glycine breath test.

It is currently problematic to confirm the clinical diagnosis of glycine encephalopathy, requiring either invasive liver biopsy for enzymatic analysis of the glycine cleavage system or exhaustive mutation analysis. Because the glycine cleavage system breaks down glycine generating carbon dioxide, we suppose that the glycine cleavage system activity could be evaluated in vivo by measuring exhaled 13CO2 after administration of [1‐13C]glycine.

Smith-Magenis Syndrome With West Syndrome in a 5-Year-Old Girl: A Long-Term Follow-Up Study

Smith-Magenis syndrome is characterized by multiple congenital anomalies and mental retardation caused by the heterozygous deletion of chromosomal region 17p11.2. We present a long-term follow-up study of a girl with Smith-Magenis syndrome and West syndrome. West syndrome became apparent at 7 months of age. Since then, mental retardation, particularly in terms of language development, became increasingly more obvious. The patients spasms and hypsarrhythmia disappeared after a course of adrenocorticotropic hormone therapy, but focal seizures reappeared at the age of 3 years and 3 months. Her craniofacial dysmorphia and mental retardation became increasingly evident compared to her condition at the onset of West syndrome. Chromosome analysis detected the characteristic 17p deletion, which was then confirmed via fluorescent in situ hybridization analysis. This is the second report of a patient with Smith-Magenis syndrome and West syndrome; taken together, these results suggest that Smith-Magenis syndrome may be a further cause of West syndrome.