Linkage studies and mutation analysis of the PDEB gene in 23 families with Leber congenital amaurosis.

The phenotype in the rd mouse is similar to the clinical presentation of Leber congenital amaurosis (LCA) in humans. Recently a nonsense mutation in the beta subunit of the cGMP phosphodiesterase (Pdeb) gene has been defined as the cause for the rd phenotype in the mouse and has raised the question as to whether mutations in the human PDEB gene might cause LCA. We have previously cloned and characterized the human homologue of the mouse Pdeb gene and have mapped it to chromosome 4p16.3. In this study, a total of 23 LCA families of various ethnic backgrounds have been investigated. Linkage analysis using highly polymorphic (CA)n microsatellites has excluded the PDEB gene as a cause for LCA in 6 families. In the remaining 17 families, we have searched for mutations in the 22 exons of the PDEB gene using single-strand gel electrophoresis (SSGE). Multiple exonic polymorphisms have been determined. However, no DNA changes in the PDEB gene have been identified in our study population which could be causative for the LCA phenotype.     

Extended HLA profile of an inbred isolate: The Schmiedeleut Hutterites of South Dakota

HLA-A, -B, -C, -DR, and -DQ typings of the Schmiedeleut Hutterites of South Dakota were collected as part of an ongoing genetic-epidemiologic study of HLA and fertility. A total of 1,082 individuals, including 852 married adults representative of the reproductive population of this isolate, were characterized for five-locus HLA haplotypes. HLA-A1, A2, A3, and A24 accounted for 75% of observed HLA-A alleles and HLA-B27, B35, B51, and B62 accounted for 55% of observed HLA-B alleles. S-leut Hutterites are derived from 68 or fewer ancestors. However, only 48 ancestral HLA haplotypes were observed and nine of these accounted for over 52% of the observed haplotypes. Measures of two-locus linkage disequilibrium derived from these haplotypes indicated that one-third to half of the observed HLA-A/B, B/DR, and A/DR allele combinations exhibited highly statistically significant linkage disequilibrium. Allele and haplotype frequencies did not differ between males and females. Recombination rates of 0.004% and 0.005% between HLA-A and -C and between HLA-B and -DR, respectively, were observed. This HLA profile points out a paucity of HLA alleles and haplotypes in this population and marked linkage disequilibrium among the HLA alleles that are present. © Wiley-Liss, Inc.     

Non-linkage of the islet amyloid polypeptide gene with Type 2 (non-insulin-dependent) diabetes mellitus

Summary Type 2 (non-insulin-dependent) diabetes is associated with the deposition of islet amyloid. The major formative peptide, islet amyloid polypeptide, has recently been characterised and an abnormality of the structure or expression of this gene is a possible candidate for the inherited component of Type 2 diabetes. A restriction fragment length polymorphism of the gene has been identified with Pvu II. To study the relationship between the islet amyloid polypeptide gene and Type 2 diabetes, two distinct genetic approaches have been undertaken. Firstly, non-linkage has been demonstrated in four pedigrees, with four normoglycaemic first degree relatives having an allele associated with diabetes in other family members, and one affected relative not having the putatively associated allele. The LOD score taking age-related penetrance into account was –1.68, making linkage unlikely (p=0.02). Secondly, in a population-based restriction fragment length polymorphism survey, no linkage disequilibrium of the alleles was found between a population of unrelated Caucasian subjects with Type 2 diabetes and a normal population. A mutation in or near the islet amyloid polypeptide gene is thus unlikely to be a common cause of Type 2 diabetes.     

红色素基因RFLP及其与情感性精神病关系的研究

以红色素基因全长ｃＤＮＡ作探针，２０例正常人，２６例双相型情感性精神病患者进行ＲＦＬＰ分析。ＳａｃＩ酶切显示：部分正常人和部分患者基因组ＤＮＡ产生的７．５ｋｂ，４．８ｋｂ，４．５ｋｂ呈多态性改变的片段。正常人具多态改变的占４５％，患者为４６．２％，按Ｘ染色体数计，正常人出现７．５ｋｂ限制性片段的频率为１４．３％，患者为３２．４％，但两者差异不显著。     

甲叉四氢叶酸还原酶C677T与精神分裂症的连锁不平衡研究

目的 通过对甲叉四氢叶酸还原酶（methylenetetrahydrofolate reductase,MTHFR)C677T错义突变与精神分裂症的连锁不平衡研究，探讨该突变与精神分裂症的关系。方法 对115个精神分裂症同胞及核心家系中，用XDT和MAPMAKER／SIBS软件系统进行MTHFRC677T与精神分裂症的连锁不平衡分析。按照不同的诊断范围将家系分类，分别在全体家系及发病年龄小于25岁的家系中进行连锁不平衡分析。结果 在4种不同的诊断分类下，对全体家系进行连锁不平衡分析未发现阳性结果。对发病年龄小于25岁的患者家系进行分析时发现，在4种不同的诊断灵感上均具有显著性意义，P值分别小于0．05及0．01。结论 MTHFR C677T错义突变可能为影响精神分裂症易感性的基因之一，尤其是在发病年龄较早的患病群体中。     

Analysis of the MTHFR 1298A-->C and 677C-->T polymorphisms as risk factors for neural tube defects

The thermolabile variant (677TT) of methylenetetrahydrofolate reductase (MTHFR) is a known risk factor for neural tube defects (NTDs). The relationship between a second MTHFR polymorphism (1298A→C) and NTD risk has been inconsistent between studies. We genotyped 276 complete NTD triads (mother, father and child affected with an NTD) and 256 controls for MTHFR 1298A→C. Our findings do not support a role for the 1298A→C polymorphism in NTDs (OR 0.85 (95% CI 0.49–1.47), p= 0.55), nor do we observe a combined effect with the 677C→T polymorphism. Electronic Publication     

Genetic variation screening and association studies of the adenylate cyclase activating polypeptide 1 (ADCYAP1) gene in patients with type 2 diabetes

Adenylate cyclase activating polypeptide 1 (ADCYAP1) is a pancreatic neuropeptide and modulates glucose-stimulated insulin secretion. The ADCYAP1 gene is located on chromosome 18p11 linked to type 2 diabetes. To test whether it is a candidate gene for type 2 diabetes, screening of the gene in Finnish and Swedish type 2 diabetic patients was done. Two novel SNPs, g.9863G>A (G54D) in exon 3 and g.12712C>G in the 3'-UTR of exon 5 of the ADCYAP1 gene (accession number X60435), were found. PCR-RFLP genotyping was then performed in a total of 253 type 2 diabetic patients and 253 non-diabetic control subjects. Transmission disequilibrium test (TDT) was performed in 132 parent-offspring trios. The G allele frequencies of g.9863G>A (G54D) and g.12712C>G of the ADCYAP1 gene were higher in type 2 diabetic patients than in non-diabetic control subjects (21.0% vs 15.8%, P=0.04; 5.3% vs 3.0%, P=0.045). However, no significant differences in clinical variables was seen between the different genotype carriers, and also no transmission distortion of the G allele of SNP g.9863G>A (G54D) was observed in 132 parent-offspring trios. The present study thus suggest that the variants in the ADCYAP1 gene may not be major influence of the susceptibility to type 2 diabetes in Finnish and Swedish Caucasians.     

Chromatin interactions in differentiating keratinocytes reveal novel atopic dermatitis– and psoriasis-associated genes

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Human growth hormone 1 (GH1) gene expression: complex haplotype-dependent influence of polymorphic variation in the proximal promoter and locus control region

The proximal promoter region of the human pituitary expressed growth hormone (GH1) gene is highly polymorphic, containing at least 15 single nucleotide polymorphisms (SNPs). This variation is manifest in 40 different haplotypes, the high diversity being explicable in terms of gene conversion, recurrent mutation, and selection. Functional analysis showed that 12 haplotypes were associated with a significantly reduced level of reporter gene expression whereas 10 haplotypes were associated with a significantly increased level. The former tend to be more prevalent in the general population than the latter (p<0.01), possibly as a consequence of selection. Although individual SNPs contributed to promoter strength in a highly interactive and non-additive fashion, haplotype partitioning was successful in identifying six SNPs as major determinants of GH1 gene expression. The prediction and functional testing of hitherto unobserved super-maximal and sub-minimal promoter haplotypes was then used to test the efficacy of the haplotype partitioning approach. Electrophoretic mobility shift assays demonstrated that five SNP sites exhibit allele-specific protein binding. An association was noted between adult height and the mean in vitro expression value corresponding to an individual's GH1 promoter haplotype combination (p=0.028) although only 3.3% of the variance of adult height was found to be explicable by reference to this parameter. Three additional SNPs, identified within sites I and II of the upstream locus control region (LCR), were ascribed to three distinct LCR haplotypes. A series of LCR-GH1 proximal promoter constructs were used to demonstrate that 1) the LCR enhanced proximal promoter activity by up to 2.8-fold depending upon proximal promoter haplotype, and that 2) the activity of a given proximal promoter haplotype was also differentially enhanced by different LCR haplotypes. The genetic basis of inter-individual differences in GH1 gene expression thus appears to be extremely complex.