A summary of mutations in the UV‐sensitive disorders: Xeroderma pigmentosum,Cockayne syndrome,and trichothiodystrophy

The human diseases xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy are caused by mutations in a set of interacting gene products, which carry out the process of nucleotide excision repair. The majority of the genes have now been cloned and many mutations in the genes identified. The relationships between the distribution of mutations in the genes and the clinical presentations can be used for diagnosis and for understanding the functions and the modes of interaction among the gene products. The summary presented here represents currently known mutations that can be used as the basis for future studies of the structure, function, and biochemical properties of the proteins involved in this set of complex disorders, and may allow determination of the critical sites for mutations leading to different clinical manifestations. The summary indicates where more data are needed for some complementation groups that have few reported mutations, and for the groups for which the gene(s) are not yet cloned. These include the Xeroderma pigmentosum (XP) variant, the trichothiodystrophy group A (TTDA), and ultraviolet sensitive syndrome (UV^s) groups. We also recommend that the XP‐group E should be defined explicitly through molecular terms, because assignment by complementation in culture has been difficult. XP‐E by this definition contains only those cell lines and patients that have mutations in the small subunit, DDB2, of a damage‐specific DNA binding protein. Hum Mutat 14:9–22, 1999. © 1999 Wiley‐Liss, Inc.     

Chronological difference in walking impairment among Japanese group A xeroderma pigmentosum (XP-A) patients with various combinations of mutation sites

Almost all Japanese group A xeroderma pigmentosum (XP-A) patients have nonsense and/or nonsense codon-leading mutations in the XP group A (XPA) gene, and develop neurological abnormalities. Walking ability is one of the most important neuromuscular functions of the patients, because it determines their daily activities. We studied the correlation between the various combinations of mutations found by PCR-RFLP in Japanese XP-A patients and their chronological walking impairment. We classified these patients into six groups. Group I: A patient who was homozygous for the mutation at codon 116 in exon 3 (Type 1 mutation) could never walk unaided. Group III: Typical patients who were homozygous for the mutation at intron 3 (Type 2 mutation) could walk unaided till 7–16 years of age. Group V: Patients who were compound heterozygous for Type 2 mutation and for the mutation at codon 228 in exon 6 (Type 3 mutation) began to develop some walking difficulty at 5–13 years of age and became unable to walk at 25–28 years of age. Group VI: A patient who was homozygous for Type 3 mutation could walk unaided without any difficulty till the age of 21. The walking ability of group II and IV patients is not known yet.     

A new Tay-Sachs disease B1 allele in exon 7 in two compound heterozygotes each with a second novel mutation.

Three novel Tay--Sachs Disease (TSD) mutations have been identified in two unrelated, non-Jewish compound heterozygous patients. A G772C transversion mutation causing an Asp258His substitution is shared by both patients. The mutant enzyme had been characterized, on the basis of previous kinetic studies (1) as a B1, or alpha-subunit active site mutation. This is the first B1 mutation not found in codon 178 (exon 5). A C508T transition causing an Arg170Trp substitution also occurred in one of the patients. The third mutation is a two base deletion occurring in exon 8 involving the loss of either nts 927-928 or 929-930 in codon 310. The deletion creates an inframe termination codon 35 bases downstream. The Arg170Trp mutation was also detected in a third unrelated TSD patient. In both families this allele was traced to French Canadian ancestors originating in the Estrie region of the province of Quebec. This mutation is the third TSD allele unique to the French Canadian population and the ancestral origins of the carrier parents are distant from the center of diffusion of the more common 7.6 kb deletion mutation which is in the eastern part of the province.     

A novel mutation in the EIF2AK3 gene with variable expressivity in two patients with Wolcott-Rallison syndrome

Mutations in the EIF2AK3 gene have been identified in patients with Wolcott-Rallison syndrome - a rare autosomal recessive disorder associated with permanent neonatal insulin-dependent diabetes. Despite the fact that different mutations have been observed in every single unrelated case reported so far, most patients presented with similar characteristics, such as osteopenia, epiphyseal dysplasia as well as hepatic and/or renal dysfunction. The EIF2AK3 gene was analyzed using a PCR-based sequencing approach in two Wolcott-Rallison patients and their parents. We report two cases from different families carrying the same and novel truncating nonsense mutation in the EIF2AK3 gene that encodes the pancreatic eukaryotic initiation factor 2alpha kinase 3. This mutation clearly displays different clinical characteristics in the two patients we examined. Remarkably, the onset of diabetes was different for the two patients, and there was also heterogeneity in other clinical manifestations. These cases illustrate the important role of alternative pathways that could, to some extent, take over or supplement a defective metabolic pathway. This supports the idea that there is no simple relationship among clinical manifestations and EIF2AK3 mutations.     

Homozygous nonsense mutation in the MCEE gene and siRNA suppression of methylmalonyl-CoA epimerase expression: a novel cause of mild methylmalonic aciduria

Methylmalonyl-CoA epimerase (MCE) catalyzes the interconversion of D- and L-methylmalonyl-CoA in the pathway responsible for the degradation of branched chain amino acids, odd chain-length fatty acids, and other metabolites. Despite the occurrence of metabolic disorders in the enzymatic step occurring immediately upstream of MCE (propionyl-CoA carboxylase) and downstream of MCE (adenosylcobalamin-dependent methylmalonyl-CoA mutase), no disease-causing mutations have been described affecting MCE itself. A patient, formerly identified as belonging to the cblA complementation group of vitamin B12 disorders but lacking mutations in the affected gene, MMAA, was tested for mutations in the MCEE gene. The patient's fibroblasts had normal levels of adenosylcobalamin compared to controls, whereas other cblA cell lines typically had reduced levels of the cofactor. As well, this patient had a milder form of methylmalonic aciduria than usually observed in cblA patients. The patient was found to be homozygous for a c.139C>T (p.R47X) mutation in MCEE by sequence analysis that was confirmed by restriction digestion of PCR products. One sibling, also with mild methylmalonic aciduria, was homozygous for the mutation. Both parents and one other sibling were heterozygous. A nearby insertion polymorphism, c.41-160_161insT, heterozygous in both parents, showed the wild-type configuration on the mutant alleles. To assess the impact of isolated MCE deficiency in cultured cells, HeLa cells were transfected with a selectable vector containing MCEE-specific small interfering RNA (siRNA) to suppress gene expression. The reduced level of MCEE mRNA resulted in the reduction of [14C]-propionate incorporation into cellular macromolecules. However, siRNA only led to a small reduction in pathway activity, suggesting that previously postulated non-enzymatic conversion of D- to L-methylmalonyl-CoA may contribute to some flux through the pathway. We conclude that the patient's MCEE defect was responsible for the mild methylmalonic aciduria, confirming a partial requirement for the enzymatic activity in humans.     

A 3′ untranslated region polymorphism rs2304277 in the DNA repair pathway gene OGG1 is a novel risk modulator for urothelial bladder carcinoma

Altered DNA repair capacity may affect an individual's susceptibility to cancers due to compromised genomic integrity. This study was designed to elucidate the association of selected polymorphisms in DNA repair genes with urothelial bladder carcinoma (UBC). OGG1 rs1052133 and rs2304277, XRCC1 rs1799782 and rs25487, XRCC3 rs861539, XPC rs2228001, and XPD rs13181 were genotyped using polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) in 200 UBC cases and 200 controls. We found association of OGG1 rs2304277 [odds ratio (OR)_GG = 3.55, 95% confidence interval (CI) = 1.79–7.06] and XPC rs2228001 (OR_AC = 2.38, 95% CI = 1.43–3.94) with UBC. In stratified analysis with respect to smoking status, OGG1 rs2304277 and XPC rs2228001 exhibited increased risk in smokers [(rs2304277 OR_GG = 4.96, 95% CI = 1.51–16.30) (rs2228001 OR_AC = 2.19, 95% CI = 1.02–4.72)] as well as nonsmokers [(rs2304277 OR_GG = 2.95, 95% CI = 1.26–6.90) (rs2228001 OR_AC = 2.57, 95% CI = 1.31–5.04)]. These polymorphisms were also associated with both low‐grade [(rs2304277 OR_GG = 3.73, 95% CI = 1.72–8.09) (rs2228001 OR_AC = 2.18, 95% CI = 1.21–3.92)] and high‐grade tumors [(rs2304277 OR_GG = 3.45, 95% CI = 1.52–7.80) (rs2228001 OR_AC = 2.81, 95% CI = 1.48–5.33)] as well as with non–muscle‐invasive bladder cancer [(rs2304277 OR_GG = 4.03, 95% CI = 1.87–8.67) (rs2228001 OR_AC = 2.14, 95% CI = 1.20–3.81)] and muscle‐invasive bladder cancer [(rs2304277 OR_GG = 3.06, 95%CI = 1.31–7.13) (rs2228001 OR_AC = 2.95, 95%CI = 1.51–5.75)]. This is the first study on DNA repair gene polymorphisms and UBC in the Pakistani population. It identifies OGG1 rs2304277 and replicates XPC rs2228001 as significant modulators of UBC susceptibility.     

Polymorphism within the distal RAD51 gene promoter is associated with colorectal cancer in a Polish population

Background: colorectal cancer (CRC) is one of the most common cancers in developed countries. Annually, over one million of new cases in the world are recorded. Majority of CRCs occur sporadically with dominant phenotype of chromosomal instability (CIN). Permanent exposure to DNA damaging agents such as ionizing radiation result in DNA double-stranded breaks, which create favorable conditions for chromosomal aberration to arise. Homologous recombination repair (HRR) is the leading process engaged in maintaining of the genome integrity. RAD51 protein was recognized as crucial in HRR. Single nucleotide polymorphisms are the primary source of genetic variation which presence in the RAD51 promoter region can affect on its expression and consequently modulate HR efficiency. Objectives: The aim of this study was to analyze the distribution of genotypes and allele frequencies of -4791A/T and -4601A/G RAD51 gene polymorphisms, followed by an assessment of their relationship with the risk of CRC. Material and methods: The study included 115 patients with confirmed CRC. Control group was consisted of 118 cancer-free individuals with a negative family history. The genotypes were identified by PCR-RFLP method. Conclusion: This study revealed statistically significant association between appearance of G/A genotype in position -4601 of RAD51 gene and CRC risk.     

Identification of a novel homozygous ALX4 mutation in two unrelated patients with frontonasal dysplasia type‐2

We report two unrelated boys with frontonasal dysplasias type‐2 (FND‐2) who shared an identical novel homozygous ALX4 mutation c.291delG (p.Q98Sfs*83). Both patients presented with a large skull defect but one had bilateral parietal meningocele‐like cysts that lie along with the bony defect and increased in size with age. Scalp alopecia, hypertelorism, and clefted alae nasi were also detected in both of them. Furthermore, impalpable gonads were noted, being unilateral in one and bilateral in the other. Neuroimaging showed small dysplastic occipital lobes with dysgyria and midline subarachnoid cyst. Additional dysplastic corpus callosum and small cerebellar vermis were observed in one patient. Parietal foramina were noted in the parents of one patient. Our findings highlight the dosage effect of ALX4 and underscore the challenges of prenatal genetic counseling. Further, the indirect role of ALX4 in the development of the occipital lobe and posterior fossa is discussed.     

A novel mutation of the insulin-like 3 gene in patients with cryptorchidism

 Two independent studies demonstrated that transgenic mice with a targeted deletion of the insulin-like 3 (INSL3) gene presented bilateral cryptorchidism. Studies in humans have investigated the possibility that mutations in the INSL3 gene are the cause of cryptorchidism. In the present study, genomic DNA was obtained from 150 patients with idiopathic cryptorchidism. DNA was amplified and the polymerase chain reaction products of both exons were sequenced. A previously unidentified missense mutation was found in only one of the patients studied. In exon 2, a heterozygous C/G substitution at nucleotide 2560, which turned asparagine into lysine at codon 86, was documented. The familial study revealed that the mother was a heterozygous carrier of the mutation and the father was a homozygote wild type. We also found three polymorphic changes, previously reported in exon 1. The Asn-into-Lys change is likely deleterious because it leads to a nonconservative amino acid substitution, changing a highly conserved residue. This mutation, located in the A-chain of the INSL3 protein, is the first mutation reported in this region. This finding provides new evidence that INSL3 is involved in testicular descent in humans; however, mutations of this gene are not a frequent cause of cryptorchidism. Received: October 15, 2002 / Accepted: November 13, 2002 Acknowledgments This work was supported by the Consejo Nacional de Ciencia y Tecnología (CONACyT), México; Grant: G29790M and by the Coordinación de Investigación en Salud, Instituto Mexicano del Seguro Social, México Grant: FP0038/1258. We thank Leonor Enciso from the Unidad de Instrumentos, Coordinación de Investigación en Salud, Instituto Mexicano del Seguro Social, for her technical assistance. Irineo Escudero is a postgraduate student from the Facultad de Medicina, Universidad Nacional Autónoma de México, México, D.F. Correspondence to:J.P. Mendez     

A novel long-QT 5 gene mutation in the C-terminus (V109I) is associated with a mild phenotype

Mutations in the human minK gene KCNE1 have been linked to autosomal dominant and autosomal recessive long-QT (LQT) syndrome, a cardiac condition predisposing to ventricular arrhythmias. minK and KvLQT1, the LQT1 gene product, form a native cardiac K+ channel that regulates the slowly delayed rectifier potassium current I(Ks). We used single-strand conformation polymorphism and sequencing techniques to identify novel KCNE1 mutations in patients with a congenital LQT syndrome of unknown genetic origin. In 150 unrelated index patients a missense mutation (V109I) was identified that significantly reduced the wild-type I(Ks) current amplitude (by 36%) when coexpressed with KvLQT1 in Xenopus oocytes. Other biophysical properties of the I(Ks) channel were not altered. Since we observed incomplete penetrance (only one of two mutation carriers could be diagnosed by clinical criteria), and the family's history was unremarkable for sudden cardiac death, the 109I allele most likely causes a mild phenotype. This finding may have implications for the occurrence of "acquired" conditions for ventricular arrhythmias and thereby the potential cardiac risk for asymptomatic mutation carriers still remains to be determined.     

一个肺泡微结石症家系中SLC34A2基因的新突变

子.此外在2例患者及先证者女儿的第2内含子发现一纯合性单核苷酸多态.结论 本家系中患者SLC34A2基因第8外显子出现新的纯合突变,提前出现终止密码子,编码截短蛋白,导致发病.所发现的第2内含子多态性意义有待深入研究.