Biomedical subjects
Publications and source records attributed to N Lévy.
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The authors report a 71-year-old woman with limb-girdle muscular dystrophy (LGMD) associated with an R27Q mutation in the CAV3 gene. Immunohistochemistry showed a >90% reduction of caveolin-3 on the sarcolemma by western blot, and anti-dysferlin immunoreactivity was reduced. This case emphasizes that an R27Q missense mutation in the CAV3 gene can lead to various clinical phenotypes including hyperCKemia, rippling muscle disease, distal myopathy, and LGMD1C.
Charcot-Marie-Tooth disease constitutes a genetically heterogeneous group of hereditary motor and sensory peripheral neuropathies. The axonal type of Charcot-Marie-Tooth is designated type 2. Six loci for autosomal dominant and three for recessive Charcot-Marie-Tooth type 2 have been reported so far. In this study we report the phenotype of autosomal recessive axonal Charcot-Marie-Tooth type 2 due to a recently-described mutation (c.892C>T-p.R298C) in a gene encoding Lamin A/C nuclear envelope proteins and the first gene in which a mutation leads to autosomal recessive Charcot-Marie-Tooth type 2. We have explored eight patients from four Algerian families. The onset is usually in the second decade and the course is rapid, involving upper limbs and proximal muscles, leading to a severe condition in less than 4 years. Many different mutations in Lamin A/C have been identified as causing variable phenotypes, such as limb girdle muscular dystrophy type 1B, autosomal dominant and recessive Emery-Dreyfuss muscular dystrophy, dilated cardiomyopathy with atrioventricular conduction defect, and Dunnigan-type familial partial lipodystrophy should prompt us to fully investigate the skeletal and cardiac muscles in patients affected with autosomal recessive Charcot-Marie-Tooth type 2 carrying a mutation in LMNA.
Microsatellite instability is characteristic of certain types of cancer, and is present in rodents lacking specific DNA mismatch repair proteins. These azoospermic mice exhibit spermatogenic defects similar to some human testicular failure patients. Therefore, we hypothesized that microsatellite instability due to deficiencies in mismatch repair genes might be an unrecognized aetiology of human testicular failure. Because these azoospermic patients are candidates for testicular sperm extraction and ICSI, transmission of mismatch repair defects to the offspring is possible. Seven microsatellite loci were analysed for instability in specimens from 41 testicular failure patients and 20 controls. Blood and testicular DNA were extracted from patient and control specimens, and amplified by PCR targeting seven microsatellite loci. DNA fragment length was analysed with an ABI Prism 310 Genotyping Machine and GeneScan software. Immunohistochemistry was performed on paraffinized testis biopsy sections and cultured testicular fibroblasts from each patient to determine if expression of the mismatch repair proteins hMSH2 and hMLH1 was normal in both somatic and germline cells. Results demonstrate that microsatellite instability and DNA mismatch repair protein defects are present in some azoospermic men, predominantly in Sertoli cell-only patients (P < 0.01 and P < 0.05 respectively). This provides evidence of a previously unrecognized aetiology of testicular failure that may be associated with cancer predisposition.
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Charcot-Marie-Tooth (CMT) disease is the most frequent hereditary peripheral neuropathy in humans. Its prevalence is about one in 2500. A subform, CMT1A, is transmitted as an autosomal dominant trait. An estimated 75% of patients are affected. This disorder has been shown to be associated with the duplication of a 1.5 Mb region of the short arm of chromosome 17, in which the PMP22 gene has been mapped. We have constructed a murine model of CMT1A by inserting into the murine genome a human YAC containing peripheral myelin protein 22 (PMP22) and its flanking controlling elements. We describe the behaviour of the C22 line (seven copies of YAC, 2.1 times PMP22 overexpression) during the myelination process. Electron microscopy, morphometry, electrophysiology, nerve conduction and expression of specific markers (e.g. Krox20) in normal and pathological Schwann cells demonstrated that PMP22 overexpression leads to a defect in the myelination of axons. The largest axons are the most affected. Only a few demyelination/remyelination processes were observed. Moreover, PMP22 overexpression probably enhances collagen synthesis by fibroblasts, before myelination, demonstrating that structures other than Schwann cells are affected by PMP22 overexpression. Classically, CMT1A was thought to be induced by a demyelination process following a phase of normal myelination, yet our data suggest that dysmyelination should be considered as a major factor for the disease.
BACKGROUND: Rett syndrome is a neurodevelopmental disorder affecting only girls; 99.5% of Rett syndrome cases are sporadic, although several familial cases have been reported. Mutations in the MECP2 gene were identified in approximately 70-80% of sporadic Rett syndrome cases. METHODS: We have screened the MECP2 gene coding region for mutations in five familial cases of Rett syndrome and studied the patterns of X chromosome inactivation (XCI) in each girl. RESULTS: We found a mutation in MECP2 in only one family. In the four families without mutation in MECP2, we found that (1) all mothers exhibit a totally skewed pattern of XCI; (2) six out of eight affected girls also have a totally skewed pattern of XCI; and (3) it is the paternally inherited X chromosome which is active in the patients with a skewed pattern of XCI. Given that the skewing of XCI is inherited in our families, we genotyped the whole X chromosome using 32 polymorphic markers and we show that a locus potentially responsible for the skewed XCI in these families could be located on the short arm of the X chromosome. CONCLUSION: These data led us to propose a model for familial Rett syndrome transmission in which two traits are inherited, an X linked locus abnormally escaping X chromosome inactivation and the presence of a skewed XCI in carrier women.
PMP22, one of the major components of myelin, is overexpressed in Charcot-Marie-Tooth type 1A (CMT1A) patients. In an attempt to determine the mechanisms by which the expression of this gene is regulated (with a view to lowering its expression in CMT1A patients), we subcloned genomic fragments covering 6kb of the promoter region in an expression vector containing the beta-galactosidase gene as reporter, and used these in transfection assays. We show that the 300bp upstream of the transcription start contain the elements required for Schwann cell specific expression of the reporter gene. This minimal promoter activity appears to be under the control of a silencer element sensitive to cAMP, located between -0.3kb and -3. 5kb from the start of transcription. Computer analysis of 2kb of the promoter predicted the presence of transcription factor binding sites, including CREB (which may be involved in the response of PMP22 expression to cAMP stimulation) and steroid receptors. Using constructs with or without the CREB sites, we were able to demonstrate that these sites are involved in silencing the PMP22 promoter activity. Lastly, we identified a region containing blocks of polymorphic CA repeats, located close to the CREB binding site, which may further influence the transcriptional activity of PMP22.
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Charcot-Marie-Tooth disease, type 1A (CMT1A) is caused in most cases by a 1.5 Mb duplication on chromosome 17p11.2 arising after unequal crossing-over between repeated sequences called CMT1A-REPs, flanking the 1.5 Mb unit. A 3.2 kb recombination hot spot has been defined, resulting in a junction fragment between EcoRI (distal CMT1A-REP) and SacI (proximal CMT1A-REP). This was further reduced to a 1.7kb EcoRI-NsiI fragment, and recently to a 731 bp hot spot region within this fragment. We describe the CMT1A-REPs-based PCR method used to identify CMT1A duplications and report on a family case in which a 29-year-old pregnant woman requested prenatal diagnosis for two successive pregnancies because her husband was affected with CMT1A. Our method enabled us to characterise the duplication in both foetuses and demonstrate that it arose from a rare recombination event taking place outside the 1.7 kb region. Since our approach is simple and enables the entire set of duplications occurring after recombination in the enlarged 3.2kb region including the hot spot to be detected, we suggest it might be considered for use in primary screening for pre- and postnatal diagnosis of CMT1A.
Deletions of the AZFc interval of the human Y chromosome are found in >5% of male patients with idiopathic infertility and are associated with a severely reduced sperm count. The most common deletion type is large (>1 Mb) and removes members of the Y-borne testis-specific gene families of BPY2, CDY1, DAZ, PRY, RBMY2 and TTY2, which are candidate AZF genes. Four exceptional individuals who have transmitted a large AZFc deletion naturally to their infertile sons have, however, been described. In three cases, transmission was to an only son, but in the fourth case a Y chromosome, shown to be deleted for all copies of DAZ, was transmitted from a father to his four infertile sons. Here we present a second family of this latter type and demonstrate that an AZFc-deleted Y chromosome lacking not only DAZ, but also BPY2 and CDY1, has been transmitted from a father to his three infertile sons. Polymerase chain reaction (PCR) and Southern blot analyses revealed no difference in the size of the AZFc deletion in the father and his sons. We propose that the father carries rare alleles of autosomal or X-linked loci which suppress the infertility that is frequently associated with the absence of AZFc.
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Twenty-two isolates of St. Louis encephalitis (SLE) virus of various geographical origins (Brazil, Argentina, Panama, Texas, Missouri, Maryland, California, and Florida) were examined for genetic variation by the base excision sequence scanning (BESS T-scan) method. A fragment was amplified in the envelope gene with the forward primer labeled in the PCR. The BESS T-scan method determined different clusters according to the profiles generated for the isolates and successfully grouped the isolates according to their geographical origins. Two major clusters, the North American cluster (cluster A) and the South and Central American cluster (cluster B), were defined. Two subgroups, the Texas-California subgroup (subgroup A1) and the Missouri-Maryland-Florida subgroup (subgroup A2), were distinguished within group A. Similarly, group B strains were subclustered to a South American subgroup (subgroup B1) and a Central American subgroup (subgroup B2). These results were consistent with those obtained by DNA sequencing analysis. The ability of the BESS T-scan method to discriminate between strains that present with high degrees of nucleotide sequence similarity indicated that this method provides reliable results and multiple applications for other virus families. The method has proven to be suitable for phylogenetic comparison and molecular epidemiology studies and may be an alternative to DNA sequencing.
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The molecular mechanism resulting in the duplication or deletion of a 1.5 Mb region of 17p11.2-p12, associated, respectively, with Charcot-Marie-Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), has been proposed to be an unequal crossing-over during meiosis between the two chromosome 17 homologues generated by misalignment of the proximal and distal CMT1A-REP repeats, two homologous sequences flanking the 1.5 Mb CMT1A/HNPP monomer unit. In a recent study of a large series of de novo cases of CMT1A and HNPP, two distinct sex-dependent mechanisms were identified. Rearrangements of paternal origin, essentially duplications, were indeed generated by unequal meiotic crossing-over between the two chromosome 17 homologues, but duplications and deletions of maternal origin resulted from an intrachromosomal process, either unequal sister chromatid exchange or, in the case of deletion, excision of an intrachromatidal loop. In order to determine how these recombinations occur, 24 de novo crossover breakpoints were localized within the 1.7 kb rearrangement hot spot by comparing the sequences of the parental CMT1A-REPs with the chimeric copy in affected offspring. Nineteen out of 21 paternal crossovers were found in a 741 bp hot spot. All the breakpoints of maternal origin (n = 3), however, were located outside this interval, but in closely flanking sequences, supporting the hypothesis that two distinct sex-dependent mechanisms are involved. Several putative recombination promoting sequences in the hot spot, which are rare or absent in the surrounding 7.8 kb, were identified.
The present study reports eight additional mutations in the connexin32 gene associated with the X-linked form of Charcot-Marie-Tooth disease. One of these mutations was found twice in two apparently unrelated families. This form of the disease is demyelinating and dominant. However, patient selection for mutational screening should not be limited to these criteria since presentation can either be familial or sporadic, and some patients may be incorrectly classified as suffering from an 'axonal' form. These new mutations complete our previously published work on 12 other mutations and enable meaningful observation in a representative sample of the French population. Mutations are found in all regions of the gene. The most frequently observed mutations were those affecting arginines and mainly involved CpG sequences. Compared with other sources, some of the mutations were present at a higher frequency in the French population.
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