Molecular genetic analysis of factor X deficiency: gene deletion and germline mosaicism

Summary A case of homozygous factor X deficiency arising from the inheritance of two non-identical gene deletions from heterozygous parents is described. One, a partial gene deletion, was localized to exons VII and VIII by a combination of Southern blotting and polymerase chain reaction (PCR) amplification of exon sequences. The other deletion, of maternal origin, probably involves the entire factor X gene. Restriction fragments associated with the exon VII + VIII deletion were present in three siblings including the homozygous proband. These fragments were however absent from the somatic cells of the father, a finding consistent with germline mosaicism.     

Biochemical and genetic analysis of butyrylcholinesterase (BChE) in a family, due to prolonged neuromuscular blockade after the use of succinylcholine

Butyrylcholinesterase (BChE) is a plasma enzyme that catalyzes the hydrolysis of choline esters, including the muscle-relaxant succinylcholine and mivacurium. Patients who present sustained neuromuscular blockade after using succinylcholine usually carry BChE variants with reduced enzyme activity or an acquired BChE deficiency. We report here the molecular basis of the BCHE gene underlying the slow catabolism of succinylcholine in a patient who underwent endoscopic nasal surgery. We measured the enzyme activity of BChE and extracted genomic DNA in order to study the promoter region and all exons of the BCHE gene of the patient, her parents and siblings. PCR products were sequenced and compared with reference sequences from GenBank. We detected that the patient and one of her brothers have two homozygous mutations: nt1615 GCA > ACA (Ala539Thr), responsible for the K variant, and nt209 GAT > GGT (Asp70Gly), which produces the atypical variant A. Her parents and two of her brothers were found to be heterozygous for the AK allele, and another brother is homozygous for the normal allele. Sequence analysis of exon 1 including 5'UTR showed that the proband and her brother are homozygous for -116GG. The AK/AK genotype is considered the most frequent in hereditary hypocholinesterasemia (44%). This work demonstrates the importance of defining the phenotype and genotype of the BCHE gene in patients who are subjected to neuromuscular block by succinylcholine, because of the risk of prolonged neuromuscular paralysis.     

A Novel Missense Mutation （L^296Q） in Cholesteryl Ester Transfer Protein Gene Related to Coronary Heart Disease

Cholesteryl ester transfer protein (CETP) is a key participant in the reverse transport of cholesterol from the peripheral tissues to the liver. To understand the role that CETP gene plays in the pathogenesis of coronary heart disease (CHD) , the promoter region, all 16 exons and adjacent intronic regions of CETP gene were screened for single nucleotide polymorphisms (SNPs) in 203 CHD patients and 209 controls by a combination of PCR, denaturing high performance liquid chromatography (DHPLC), molecular cloning, and DNA sequencing. A novel missense mutation in the CETP gene was identified. This mutation (L296Q) was a T-to-A conversion at codon 296 of exon 10 which replaced the codon for leucine (CTG) with the codon for glutamine (CAG). Association study revealed that L296Q mutation was associated with CHD with a significantly higher mutant allele frequency in the CHD patients than that in the controls (0. 160 vs. 0.091,x2= 9.014, P = 0.003), and that the odds ratio for the development of CHD was 1.83 for     

Gene analysis of the N-terminal region of the estrogen receptor alpha in preeclampsia

Alterations in the NH(2)-terminal region of the estrogen receptor alpha (ERalpha) gene expressed in placental bed tissue may be implicated in the development of preeclampsia, the pathogenesis of which involves the spiral arteries. Therefore, mutations and polymorphisms on exons 1 and 2 of the gene encoding ERalpha were studied. Placental bed biopsies were taken from 20 healthy, normotensive pregnant women and 16 preeclamptic patients. DNA was extracted from the tissue and exon 1 and exon 2 were amplified by PCR prior to denaturing gradient gel electrophoresis analysis or to single stranded conformational polymorphism analysis. In exon 1, a codon 10 polymorphism, either homozygous for the wild type gene, homozygous for the mutant type gene, or heterozygous, was revealed in both patients and healthy individuals. A codon 87 polymorphism, homozygous for the wild type gene, was detected in both groups. No mutations or polymorphisms were found in exon 2. The allele distribution for either codon 10 or 87 between patients and healthy individuals showed no significant differences. In conclusion, genetic alterations in the NH(2)-terminal region of the ERalpha molecule are not correlated with preeclampsia.     

Molecular analysis of Hurler syndrome in Druze and Muslim Arab patients in Israel: multiple allelic mutations of the IDUA gene in a small geographic area.

The mutations underlying Hurler syndrome (mucopolysaccharidosis IH) in Druze and Muslim Israeli Arab patients have been characterized. Four alleles were identified, using a combination of (a) PCR amplification of reverse-transcribed RNA or genomic DNA segments, (b) cycle sequencing of PCR products, and (c) restriction-enzyme analysis. One allele has two amino acid substitutions, Gly409-->Arg in exon 9 and Ter-->Cys in exon 14. The other three alleles have mutations in exon 2 (Tyr64-->Ter), exon 7 (Gln310-->Ter), or exon 8 (Thr366-->Pro). Transfection of mutagenized cDNAs into Cos-1 cells showed that two missense mutations, Thr366-->Pro and Ter-->Cys, permitted the expression of only trace amounts of alpha-L-iduronidase activity, whereas Gly409-->Arg permitted the expression of 60% as much enzyme as did the normal cDNA. The nonsense mutations were associated with abnormalities of RNA processing: (1) both a very low level of mRNA and skipping of exon 2 for Tyr64-->Ter and (2) utilization of a cryptic splice site for Gln310-->Ter. In all instances, the probands were found homozygous, and the parents heterozygous, for the mutant alleles, as anticipated from the consanguinity in each family. The two-mutation allele was identified in a family from Gaza; the other three alleles were found in seven families, five of them Druze, residing in a very small area of northern Israel. Since such clustering suggests a classic founder effect, the presence of three mutant alleles of the IDUA gene was unexpected.     

Heterotrisomy, a significant contributing factor to ventricular septal defect associated with Down syndrome?

Down syndrome (DS; trisomy 21) is associated with a wide range of variable clinical features, one of the most common being congenital heart defects (CHD). We used molecular genetic techniques to study the inheritance of genes on chromosome 21 in children with DS and CHD. Polymorphic markers on the long arm of chromosome 21 were analysed in 99 families who had a child with DS. Of these, 60 children had a CHD and 39 children had no CHD. Heterotrisomy describes the inheritance of an allele from each of three different grandparents. In some cases heterotrisomy will involve the inheritance of three different alleles. Heterotrisomic regions were defined as those showing retention of non-disjoining parental heterozygosity at polymorphic loci in the non-disjoined chromosomes of children with DS. Using polymorphic non-coding markers, we identified a consistent 9.6-cM minimum region (D21S167-HMG14) of heterotrisomy in children with DS and ventricular septal defect (VSD). Comparing individuals with DS and VSD to all others with DS (those either with no CHD or with any other CHD combined) shows the individuals with DS and VSD to have significantly more non-reduction or heterotrisomy in this region (P=0.006, Fisher's exact test, two-tailed). We postulate that heterotrisomy for a gene or genes in this region is a contributing factor to the pathogenesis of VSD in trisomy 21 either through the presence of three different specific alleles or through the presence of specific combinations of alleles.     

Molecular signatures of cardiac defects in down syndrome lymphoblastoid cell lines suggest altered ciliome and hedgehog pathways

Forty percent of people with Down syndrome exhibit heart defects, most often an atrioventricular septal defect (AVSD) and less frequently a ventricular septal defect (VSD) or atrial septal defect (ASD). Lymphoblastoid cell lines (LCLs) were established from lymphocytes of individuals with trisomy 21, the chromosomal abnormality causing Down syndrome. Gene expression profiles generated from DNA microarrays of LCLs from individuals without heart defects (CHD(-); n?=?22) were compared with those of LCLs from patients with cardiac malformations (CHD(+); n?=?21). After quantile normalization, principal component analysis revealed that AVSD carriers could be distinguished from a combined group of ASD or VSD (ASD+VSD) carriers. From 9,758 expressed genes, we identified 889 and 1,016 genes differentially expressed between CHD(-) and AVSD and CHD(-) and ASD+VSD, respectively, with only 119 genes in common. A specific chromosomal enrichment was found in each group of affected genes. Among the differentially expressed genes, more than 65% are expressed in human or mouse fetal heart tissues (GEO dataset). Additional LCLs from new groups of AVSD and ASD+VSD patients were analyzed by quantitative PCR; observed expression ratios were similar to microarray results. Analysis of GO categories revealed enrichment of genes from pathways regulating clathrin-mediated endocytosis in patients with AVSD and of genes involved in semaphorin-plexin-driven cardiogenesis and the formation of cytoplasmic microtubules in patients with ASD-VSD. A pathway-oriented search revealed enrichment in the ciliome for both groups and a specific enrichment in Hedgehog and Jak-stat pathways among ASD+VSD patients. These genes or related pathways are therefore potentially involved in normal cardiogenesis as well as in cardiac malformations observed in individuals with trisomy 21.     

200 例新生儿心脏彩超筛查先心病结果分析

目的:了解新生儿先天性心脏病(简称先心病)的发病情况,获得基本资料,为制定和采取干预措施提供决策依据。方法:将新生儿心脏彩超列入常规检查项目,选择西京医院产科2011年6月13日至7月23日出生的200名新生儿进行心脏彩超检查,筛查率为100%。结果:正常的为170例,占85%,其中需观察、随访的131例。异常的为30例,发病率占百分之15%,其中复杂先心病3例。30例先心病患儿中,以ASD+PDA类型心脏病最多,占56.67%;其次是ASD,占16.67%;VSD+PDA和VSD+PDA+PFO类型分别占6.67%;检出复杂先心病类型单室+房间隔缺损+肺动脉瓣狭窄、单房单室、部分型心内膜垫缺损+ASD+二尖瓣前瓣裂,分别占3.33%。结论:新生儿先心病的发病率较高,采用心脏彩超等检查项目筛查是非常必要的,需认识导致新生儿先心病的原因,尽早发现先心病患儿,并做好先心病患儿的随访工作,为及时进行干预提供保障。     

An intronic polymorphism of the hMLH1 gene contributes toward incomplete genetic testing for HNPCC

Hereditary non-polyposis colorectal cancer (HNPCC) is a common hereditary cancer. Genetic testing is complicated by the multiple DNA mismatch repair genes that underlie the disorder. Many suspected HNPCC families have no germ-line mutation identified. We reassessed an unusual family that appeared to have 2 individuals homozygous for a germline mutation within exon 1 of the hMLH1 gene. A few rare individuals with two inherited mutations in one of the mismatch repair genes have been reported and appear to have a distinct clinical appearance. However, there were no clinical features in the family discussed here that were consistent with constitutive lack of hMLH1. Redesigning the intronic primers for exon 1 identified a common polymorphism located within the original intronic primer site. The polymorphism prevented amplification of the wild-type allele, giving the erroneous appearance of homozygous inheritance of the mutated allele. Likewise, common intronic polymorphisms, if located within primer sequences on the chromosome harboring the HNPCC germ-line mutation could restrict amplification to only the wild-type allele, which may contribute significantly to the low success rate of identifying mutations in HNPCC families.     

A missense mutation (I278T) in the cystathionine beta-synthase gene prevalent in pyridoxine-responsive homocystinuria and associated with mild clinical phenotype.

Cystathionine beta-synthase (CBS) deficiency is an autosomal recessive disorder characterized by homocystinuria and multisystem clinical disease. Patients responsive to pyridoxine usually have a milder clinical phenotype than do nonresponsive patients, and we studied the molecular pathology of this disorder in an attempt to understand the molecular basis of the clinical variation. We previously reported a T833C transition in exon 8 causing a substitution of threonine for isoleucine at codon 278 (I278T). By PCR amplification and sequencing of exon 8 from genomic DNA we have now detected the I278T mutation in 7 of 11 patients with in vivo pyridoxine responsiveness and in 0 of 27 pyridoxine-nonresponsive patients. Two pyridoxine-responsive patients are homozygous and five are heterozygous for I278T. We have now observed the I278T mutation in 41% (9 of 22) of the independent alleles in pyridoxine-responsive patients of varied ethnic backgrounds. In two of the compound heterozygotes we identified a novel mutation (G139R and E144K) in the other allele. The finding that the two patients who are homozygous for I278T have only ectopia lentis and mild bone demineralization suggests that this mutation is associated with both in vivo pyridoxine responsiveness and mild clinical disease. Compound heterozygous patients who have one copy of this missense mutation are likely to retain some degree of pyridoxine responsiveness.     

More than one mutant allele causes infantile Tay-Sachs disease in French-Canadians

Two Tay-Sachs disease (TSD) patients of French-Canadian origin were shown by Myerowitz and Hogikyan to be homozygous for a 7.6-kb deletion mutation at the 5' end of the hexosaminidase A α-subunit gene. In order to determine whether all French-Canadian TSD patients were homozygotes for the deletion allele and to assess the geographic origins of TSD in this population, we ascertained 12 TSD families of French-Canadian origin and screened for occurrence of mutations associated with infantile TSD. DNA samples were obtained from 12 French-Canadian TSD families. Samples were analyzed using polymerase-chain-reaction (PCR) amplification followed by hybridization to allele-specific oligonucleotides (ASO) or by restriction analysis of PCR products. In some cases Southern analysis of genomic DNA was performed. Eighteen of the 22 independently segregating mutant chromosomes in this sample carried the 7.6-kb deletion mutation at the 5' end of the gene. One chromosome carried the 4-nucleotide insertion in exon 11 (a “Jewish” mutation). In this population no individuals were detected who had the substitution at the splice junction of exon 12 previously identified in Ashkenazi Jews. One chromosome carried an undescribed B¹ mutation; this allele came from a parent of non-French-Canadian origin. Patients in three families carried TSD alleles different from any of the above mutations. The 5' deletion mutation clusters in persons originating in southeastern Quebec (Gaspé) and adjacent counties of northern New Brunswick.