Frequency and ethnic distribution of the common DHCR7 mutation in Smith‐Lemli‐Opitz syndrome

Smith‐Lemli‐Opitz syndrome (SLOS) is an inherited multiple malformation syndrome caused by enzymatic deficiency of 3β‐hydroxysterol‐Δ⁷‐reductase (DHCR7). SLOS is thought to be most common among European Caucasians, with an incidence of 1 in 20,000 to 1 in 30,000 births. To define the carrier rate and ethnic distribution of SLOS, we screened DNA samples from 2,978 unrelated individuals for the most common SLOS mutation (IVS8‐1G→C). Twenty‐four heterozygotes of the IVS8‐1G→C mutation were detected in 2,978 individuals of European Caucasian and Black backgrounds. For European Caucasians, the carrier rate for SLOS may be as high as 1 in 30, suggesting an incidence of 1 in 1,700 to 1 in 13,400. This high number is supported by the recent observation of newborn and prenatal incidence of 1 in 22,000 in the Caucasian population. Ours is the first report of the IVS8‐1G→C mutation in persons of African ancestry. Published 2001 Wiley‐Liss, Inc.     

Assessment of the genetic causes of recessive childhood non-syndromic deafness in the UK - implications for genetic testing

Approximately one in 2000 children is born with a genetic hearing impairment, mostly inherited as a non-syndromic, autosomal recessive trait, for which more than 30 different genes have been identified. Previous studies have shown that one of these genes, connexin 26 (GJB2), accounts for 30-60% of such deafness, but the relative contribution of the many other genes is not known, especially in the outbred UK population. This lack of knowledge hampers the development of diagnostic genetic services for deafness. In an effort to determine the molecular aetiology of deafness in the population, 142 sib pairs with early-onset, non-syndromic hearing impairment were recruited. Those in whom deafness could not be attributed to GJB2 mutations were investigated further for other mapped genes. The genetic basis of 55 cases (38.7%) was established, 33.1% being due to mutations in the GJB2 gene and 3.5% due to mutations in SLC26A4. None of the remaining 26 loci investigated made a significant contribution to deafness in a Caucasian population. We suggest that screening the GJB2 and SLC26A4 genes should form the basis of any genetic testing programme for childhood deafness and highlight a number of important issues for consideration and future work.     

Somatic spectrum of cancer-associated single basepair substitutions in the TP53 gene is determined mainly by endogenous mechanisms of mutation and by selection

The spectrum of somatic TP53 single basepair substitutions detected in 955 cancers was compared with that of 2,224 different germline mutations in 279 different human genes (other than TP53), reported as the cause of inherited disease. This comparison reveals that, disregarding a relatively small subset (12%) of TP53 mutations that probably result from the action of exogenous mutagens, both the relative rates and the nearest-neighbor spectra of single basepair substitutions are similar in the two datasets. This spectral resemblance suggests that a substantial proportion of cancer-associated somatic TP53 mutations result from endogenous cellular mechanisms. The likelihood of clinical observation of a particular mutation type differs, however, between tumors and genetic diseases, when the chemical properties of the resulting amino acid substitutions are considered. Together with a sixfold higher observation likelihood for mutations at evolutionary conserved residues, this finding argues that selection is a critical factor in determining which TP53 mutations are found to be associated with human cancer. © 1995 Wiley-Liss, Inc.     

Molecular genetics of pseudoxanthoma elasticum: type and frequency of mutations in ABCC6

Pseudoxanthoma elasticum (PXE) is a systemic heritable disorder that affects the elastic tissue in the skin, eye, and cardiovascular system. Mutations in the ABCC6 gene cause PXE. We performed a mutation screen in ABCC6 using haplotype analysis in conjunction with direct sequencing to achieve a mutation detection rate of 97%. This screen consisted of 170 PXE chromosomes in 81 families, and detected 59 distinct mutations (32 missense, eight nonsense, and six likely splice-site point mutations; one small insertion; and seven small and five large deletions). Forty-three of these mutations are novel variants, which increases the total number of PXE mutations to 121. While most mutations are rare, three nonsense mutations, a splice donor site mutation, and the large deletion comprising exons 23-29 (c.2996_4208del) were identified as relatively frequent PXE mutations at 26%, 5%, 3.5%, 3%, and 11%, respectively. Chromosomal haplotyping with two proximal and two distal polymorphic markers flanking ABCC6 demonstrated that most chromosomes that carry these relatively frequent PXE mutations have related haplotypes specific for these mutations, which suggests that these chromosomes originate from single founder mutations. The types of mutations found support loss-of-function as the molecular mechanism for the PXE phenotype. In 76 of the 81 families, the affected individuals were either homozygous for the same mutation or compound heterozygous for two mutations. In the remaining five families with one uncovered mutation, affected showed allelic compound heterozygosity for the cosegregating PXE haplotype. This demonstrates pseudo-dominance as the relevant inheritance mechanism, since disease transmission to the next generation always requires one mutant allelic variant from each parent. In contrast to other previous clinical and molecular claims, our results show evidence only for recessive PXE. This has profound consequences for the genetic counseling of families with PXE.     

Three novel PROC gene lesions causing protein C deficiency

Hallam PJ, Mannucci P, Tripodi A, Bevan D, Laursen B, Tengborn L, Wacey A, Cooper DN. Three novel PROC gene lesions causing protein C deficiency. Clin Genet 1998: 54: 231–233. 0 Munksgaard, 1998
Missense mutations. three of them novel (Am210→Val, Asn248→ Ile, Ah355→Val), were found in the protein c ( PROC ) genes of 7 patients with inherited protein C deficiency associated with venous thrombosis. Comparison with the phenotypic effects of mutations in the analogous residues of factor IX causing hdernophilia B and the use of molecular modelling has provided explanations as to how these lesions might alter either the structure, function or secretion of the protein C molecules encoded.     

Nuclear suppressors of the mitochondrial mutation oxi1-V25 in Saccharomyces cerevisiae

Summary Ten nuclear suppressors (nam mutations) of the mitochondrial oxi1-V25 ochre mutation are characterized. They restore to some extent the functional form of cytochrome oxidase, as judged by the results of growth tests, cytochrome spectra, cytochrome oxidase activities, and electrophoresis of the products of mitochondrial translation. The nam mutants can suppress some mit ^– mutations mapping in four mitochondrial genes. They act on a number of chain-terminating mit ^– mutations. When grown on glycerol medium some double mutants nam _x-V25 show an increased sensitivity to paromomycin, while the growth of others is stimulated by the drug. The nam mutants are probably omnipotent suppressors resulting from mutations in nuclear gene(s) specifying mitoribosomal protein(s).     

Combined breast conservation therapy versus mastectomy for BRCA mutation carriers – A systematic review and meta-analysis

BackgroundThe non-inferiority of combined breast conservation surgery (BCS) and radiotherapy (breast conservation therapy or BCT) compared to mastectomy in sporadic breast cancer cases is well recognised. Uncertainty remains regarding optimal surgical practice in BRCA mutation carriers.AimsTo evaluate the oncological safety of combined BCT versus mastectomy in BRCA mutation carriers following breast cancer diagnosis.MethodsA systematic review was performed as per PRISMA and MOOSE guidelines. Observational studies comparing BCS and mastectomy in BRCA carriers were identified. Dichotomous variables were pooled as odds ratios (OR) using the Mantel–Haenszel method. Log hazard ratios (lnHR) for locoregional recurrence (LRR), contralateral breast cancer, disease-free and overall survival and their standard errors were calculated from Kaplan-Meier or cox-regression analyses and pooled using the inverse variance method.ResultsTwenty three studies of 3807 patients met inclusion criteria; 2200 (57.7%) were BRCA1 and 1212 (31.8%) were BRCA2 carriers. Median age at diagnosis was 41 years with 96 months follow up. BCS was performed on 2157 (56.7%) while 1408 (41.5%) underwent mastectomy. An increased risk of LRR was observed in patients treated with BCS (HR:4.54, 95% Confidence Interval: 2.77–7.42, P < 0.001, heterogeneity (I²) = 0%). However, the risks of contralateral breast cancer (HR:1.51, 95%CI: 0.44–5.11, P = 0.510, I² = 80%), disease recurrence (HR:1.16, 95%CI: 0.78–1.72, P = 0.470, I² = 44%), disease-specific recurrence (HR:1.58, 95%CI: 0.79–3.15, P = 0.200, I² = 38%) and death (HR:1.10, 95%CI: 0.72–1.69, P = 0.660, I² = 38%) were equivalent for combined BCT and mastectomy.ConclusionsSurvival outcomes following combined BCT is comparable to mastectomy in BRCA carriers. However, the risk of LRR is increased. Patient counselling should be tailored to incorporate these findings.     

次抑菌浓度喹诺酮类药物体外诱导人型支原体ParE基因突变的研究

目的　探讨体外诱导耐喹诺酮类药物的Mh的ParE基因突变情况。方法　以含氧氟沙星、左旋氧氟沙星、盐酸环丙沙星、司帕沙星的培养基培养Mh标准敏感株 12代后 ,将其ParE基因进行PCR扩增 ,分析其核苷酸序列。结果　氧氟沙星、左旋氧氟沙星诱导Mh发生 70位的G→A的突变 ,导致 4 2 6位的天冬氨酸转变为天冬酰胺。结论　ParE基因中 70位的突变与Mh耐喹诺酮类药物有关。     

Novel chloride channel gene mutations in two unrelated Japanese families with Becker's autosomal recessive generalized myotonia

We investigated the skeletal muscle voltage-gated chloride channel gene (CLCN1) in two unrelated Japanese patients with Becker's myotonia congenita. The non-myotonic parents of each patient were consanguineous. The proband of each family shares generalized myotonia, transient weakness after rest, and leg muscle hypertrophy. However, the disease severity related to the degree of myotonia differed, even in view of the response to long train nerve stimulation tests. CLCN1 gene analysis revealed a novel Ala659Val missense mutation identified to be homozygous in the more severe patient, while a novel Gln445Stop nonsense mutation was present in the other patient. Both mutations were absent in 90 Japanese normal controls. This is the first report of Japanese cases of Becker's myotonia congenita with CLCN1 gene mutations.     

Relation between genotype and phenotype in Swedish phenylketonuria and hyperphenylalaninemia patients

Phenylketonuria (PKU) and hyperphenylalaninemia (HPA) are caused mostly by an inherited (autosomal recessive) deficiency in hepatic phenylalanine hydroxylase (PAH) activity. More than 50 PAH mutations have ben reported. The goal of the present study was to examine the molecular basis for the clinical heterogeneity of Swedish PKU and HPA patients. Mutations were identified through allele-specific oligonucleotide hybridization or DNA sequencing on 128 of the 176 mutant alleles (73%). Three mutations (R408W, Y414C and IVS12) together accounted for 56% of all mutant alleles and ten relatively infrequent mutations were found on another 17% of all mutant alleles. Patients from 50 of the 88 families (57%) had identified mutations in both PAH genes and allowed use to compare the clinical effects of different combinations of PAH mutations. The in vitro activity of all of these mutations, including the newly identified G272X and L364, have been tested in a eukaryotic expression system. There was a strong relationship between the average in vitro PAH activity of the two mutant enzymes and both the phenylalanine tolerance and the neonatal pretreatment serum phenylalanine concentration. This confirms previous observations in Danish and German PKU patients that disease phenotype is a consequence of the nature of the mutations at the PAH locus and not significantly influenced by other loci. The sample population in the previous study did not, however, include mild HPA patients, and the observed correlation is thus restricted to severe and moderate mutant alleles. Since a comparatively high proportion of the Swedish patients were mildly affected, we have provided additional evidence that this correlation is valid throughout a continuous spectrum of clinical varieties. PAH genotyping could therefore help predict prognosis of a recently diagnosed PKU or HPA child.