The contribution of germline rearrangements to the spectrum of BRCA2 mutations

BACKGROUND

Few germline BRCA2 rearrangements have been described compared with the large number of germline rearrangements reported in the BRCA1 gene. However, some BRCA2 rearrangements have been reported in families that included at least one case of male breast cancer.

OBJECTIVE

To estimate the contribution of large genomic rearrangements to the spectrum of BRCA2 defects.

METHODS

Quantitative multiplex PCR of short fluorescent fragments (QMPSF) was used to screen the BRCA2 gene for germline rearrangements in highly selected families. QMPSF was previously used to detect heterozygous deletions/duplications in many genes including BRCA1 and BRCA2.

RESULTS

We selected a subgroup of 194 high risk families with four or more breast cancers with an average age at diagnosis of < or = 50 years, who were recruited through 14 genetic counselling centres in France and one centre in Switzerland. BRCA2 mutations were detected in 18.6% (36 index cases) and BRCA1 mutations in 12.4% (24 index cases) of these families. Of the 134 BRCA1/2 negative index cases in this subgroup, 120 were screened for large rearrangements of BRCA2 using QMPSF. Novel and distinct BRCA2 deletions were detected in three families and their boundaries were determined. We found that genomic rearrangements represent 7.7% (95% confidence interval 0% to 16%) of the BRCA2 mutation spectrum.

CONCLUSION

The molecular diagnosis of breast cancer predisposition should include screening for BRCA2 rearrangements, at least in families with a high probability of BRCA2 defects.

Late neurological presentations of Wilson disease patients in French population and identification of 8 novel mutations in the ATP7B gene

Wilson disease (WD) is an autosomal recessive disorder of copper biliary excretion caused by an impaired function of ATP7B, a metal-transporting P-type ATPase encoded by WD gene. It results in copper accumulation, mostly in liver and brain tissues. Mutation analysis was carried out on 11 WD French unrelated patients presenting a predominant neurological form of this illness. SSCP and dHPLC analysis followed by sequencing of the 21 exons and their flanking introns were performed. Thirteen different mutations in a total of 17, and, among them, 10 novel variants were evidenced. Two deletions (c.654_655delCC and c.1745_1746delTA), 4 missense mutations (p.F763Y, p.G843R, p.D918A and p.L979Q), 1 nonsense mutation (p.Q1200X), 1 splice site mutation (c.1947-1G>C) and 2 intronic silent substitutions (c.2448-25G>T and c.3412+13T>A) were detected. These data extend the mutational spectrum of the disease, already known to be a very heterogeneous genetic disorder. As compared to hepatic manifestations, the phenotypes associated to these mutations confirm that neurological presentations associated with other mutations than p.H1069Q are also often late in their onset. Most of these neurological forms probably correspond to an attenuated impairment of copper metabolism, as compared to hepatic forms of the disease, mostly diagnosed earlier.

La maladie de Wilson

Wilson disease is an autosomal recessive disorder of copper overload. A principal characteristic of this disease is its wide phenotypic and genotypic variability. Its results from mutations of the ATP 7B gene located on chromosome 13, that encodes a hepatic copper transport protein. More than 300 mutations of this gene have been identified. This protein ensures the transport of copper in the hepatocyte, its incorporation with the apoceruloplasmin and its biliary excretion. The clinical manifestations are heterogeneous as well in their presentation, dominated by the neuropsychiatric and hepatic symptoms, as in the age of the first symptoms. Early recognition and initiation of therapy with chelators or zinc are essential for prognosis. Liver transplantation is indicated in cases with fulminant hepatitis, end-stage liver cirrhosis and should be considered in the therapy resistant neurological forms. A regular follow-up with monitoring of adverse effects of treatment and compliance is essential. Any discontinuation of treatments will involve, within a very variable time, but in constant manner, a reappearance or a reaggravation of the signs. Such relapses are often brutal and can be extremely serious, especially since response to subsequent treatment is often poor.

Extensive cortico-subcortical lesions in Wilson's disease: clinico-pathological study of two cases

Wilson's disease (WD) with extensive cortico-subcortical lesions represents a rare neuropathological subgroup, the pathogenesis of which is not clearly determined. We report two new cases with identical lesions. In the families of each of the patient, there were mutations in the ATPase7B gene, especially in the family of proband 1, and in the first cousin of proband 2. These cases included massive destruction of the white matter in superior gyri, mostly frontal, extending to the deep cortex with neuronal loss and capillary proliferation. Astrocytes were of Alzheimer type 1 and 2; and type 1 were labeled by anti-metallothionein. Opalski cells were abundant and their macrophagic lineage was confirmed by immunostaining. Among the possible mechanisms proposed, the role of vascular factors and penicillamine treatment could be excluded. Cerebral copper content in white matter and putamen of case 1 was at the same level as in common WD but accumulation of unbound copper in the white matter was a distinctive feature, which suggested a pathological neurotoxic effect.

[Wilson disease: clinical and biological aspects]

Wilson disease is an autosomal recessive disorder of copper excess. This illness results from mutations of the ATP7B gene (chromosome 13, MIM# 277900). The discovery of the gene allowed a better understanding of cytosolic copper trafficking and its relationship with ceruloplasmin synthesis. Symptomatic patients may present with hepatic, neurologic or psychiatric forms. Clinical and phenotypic evidences provide only presumptive arguments for this disease which can be routinely assessed by molecular analysis. This genetic disease which can be efficiently treated was formerly biologically suspected after a careful but sometimes invasive study of copper metabolism. Genetic advances can now give a definite answer using linkage analysis and research for disease-causing mutations. However, this diagnosis strategy is limited since currently over 320 mutations and 80 polymorphisms have been currently identified.

Strontium ranelate inhibits bone resorption while maintaining bone formation in alveolar bone in monkeys (Macaca fascicularis)

Strontium ranelate (S12911) has previously been shown to stimulate bone formation and inhibit bone resorption in rats. To determine whether strontium ranelate affects normal bone remodeling, we studied the effect of strontium ranelate on alveolar bone in monkeys. Strontium ranelate, at dosages of 100, 275, and 750 mg/kg per day, or vehicle, were given by gavage to 31 normal adult monkeys (Macaca fascicularis) (15 males, 16 females), aged 3-4 years. Treatment for 6 months with strontium ranelate resulted in an increase in plasma strontium concentration. Histomorphometric analyses of indices of bone formation and resorption were determined in standardized areas of alveolar bone. Treatment with strontium ranelate decreased the histomorphometric indices of bone resorption (osteoclast surface and number) with a maximal significant effect at the highest dose tested. In contrast to this inhibitory effect on bone resorption, strontium ranelate maintained bone formation. Although the amount of osteoid tended to increase, strontium ranelate, even at the highest dose, had no deleterious effect on bone mineralization, as evaluated by mineral apposition rate and osteoid thickness. These findings show that strontium ranelate decreases indices of bone resorption while maintaining bone formation in the alveolar bone in monkeys.

Detection of protein truncating mutations in exons 1-14 of the APC gene using an in vivo fusion protein assay. Mutations in brief no. 214. Online

About 80% of the mutations identified to date in the Adenomatous Polyposis Coli (APC) gene have been found in the 5' half of the coding sequence, the vast majority of which (>95%) are nonsense or frameshift mutations that result in the loss of the carboxyl terminus of APC protein. Using a stop codon assay in yeast recently developed by others (Ishioka et al., 1997), we have screened the 5' half of the APC gene for mutations in 7 unrelated families affected with Familial Adenomatous Polyposis. The assay relies on the expression of a yeast reporter gene fused in frame to one of 3 contiguous segments of the APC open reading frame. Here we report on the detection by this assay of 5 germline mutations, 4 of which lie upstream of exon 15, where lesions appear to be sometimes difficult to detect by standard methods.

Are copper, zinc and selenium in erythrocytes valuable biological indexes of nutrition and pathology?

The real significance of the level of trace elements copper, zinc and selenium in erythrocytes is still a matter of debate. This review is an evaluation of the potential value of copper, zinc and selenium in red blood cells in physiology, nutrition and pathology, taking into account the other commonly used indices and the analytical difficulty encountered for erythrocyte determinations. The main analytical methods and reference values in erythrocytes are also presented. The literature of the last 3 decades was analyzed. On the basis of these papers, the role of erythrocyte copper in various pathologies should be re-investigated, especially when they include inflammatory processes or hormonal changes. The main interest of zinc determination in red blood cells concerns thyroid pathology. In general, the value of selenium in erythrocytes agrees with selenium in serum and its determination is often unnecessary.

N-acetyltransferase 2 influences cancer prevalence in hMLH1/hMSH2 mutation carriers

Hereditary nonpolyposis colorectal cancer (HNPCC), an inherited cancer predisposition syndrome, has been associated with germline mutations in DNA mismatch repair (MMR) genes. Because a deficiency in MMR does not predict a specific cancer phenotype, modifying genes may account in part for the variation in disease expression. We determined the N-acetyltransferase 2 (NAT2) genotype in 26 unaffected and 52 cancer-affected hMLH1/hMSH2 mutation carriers coming from 21 Swiss HNPCC families. Slow acetylators were found to be significantly (P < 0.03) more prevalent in the group of affected mutation carriers. Our results suggest a protective effect of the NAT2 rapid acetylator phenotype, an observation that could have implications for genetic counseling and management of MMR gene mutation carriers.

PCR-mediated detection of a polymorphism in the ATM gene

In this report, the frequency of the G-->A transition polymorphism at nucleotide 5557 in exon 39 of the coding sequence of the gene mutated in ataxia-telangiectasia (ATM) was analysed. The frequency of the A and G alleles was estimated in the general population at 0. 15 and 0.85, respectively. This polymorphism can be identified by single-strand conformation polymorphism (SSCP) and by a simple and rapid Dde I digestion after polymerase chain reaction (PCR)-mediated site directed mutagenesis (PSDM).