Altered Chromosomal Positioning, Compaction, and Gene Expression with a Lamin A/C Gene Mutation

Lamins A and C, encoded by the LMNA gene, are filamentous proteins that form the core scaffold of the nuclear lamina. Dominant LMNA gene mutations cause multiple human diseases including cardiac and skeletal myopathies. The nuclear lamina is thought to regulate gene expression by its direct interaction with chromatin. LMNA gene mutations may mediate disease by disrupting normal gene expression.To investigate the hypothesis that mutant lamin A/C changes the lamina's ability to interact with chromatin, we studied gene misexpression resulting from the cardiomyopathic LMNA E161K mutation and correlated this with changes in chromosome positioning. We identified clusters of misexpressed genes and examined the nuclear positioning of two such genomic clusters, each harboring genes relevant to striated muscle disease including LMO7 and MBNL2. Both gene clusters were found to be more centrally positioned in LMNA-mutant nuclei. Additionally, these loci were less compacted. In LMNA mutant heart and fibroblasts, we found that chromosome 13 had a disproportionately high fraction of misexpressed genes. Using three-dimensional fluorescence in situ hybridization we found that the entire territory of chromosome 13 was displaced towards the center of the nucleus in LMNA mutant fibroblasts. Additional cardiomyopathic LMNA gene mutations were also shown to have abnormal positioning of chromosome 13, although in the opposite direction.These data support a model in which LMNA mutations perturb the intranuclear positioning and compaction of chromosomal domains and provide a mechanism by which gene expression may be altered

Promouvoir une contraception choisie pour prévenir les IVG en médecine générale

DIJON-BU Médecine Pharmacie (212312103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Rapid and Direct Detection of the Most Frequent Mediterranean β-Thalassemic Mutations by Multiplex Allele-Specific Enzymatic Amplification

A rapid nonradioactive method for the diagnosis of the most frequent Mediterranean β-thalassemic mutations is described based on a multiplex allele-specific polymerase chain reaction (PCR). This method allows direct detection of normal or mutated alleles on genomic DNA. We have used this approach to detect the most frequent Mediterranean mutations IVS-1 nt 100 (G → A) and 39 nonsense (C → T). For each mutation three allele-specific oligonucleotides were used: one common upstream primer and two downstream primers differing in their terminal 3\u27 nucleotide (one specific for the normal allele and one for the mutant allele). For each sample two PCR reactions were performed in parallel using one case IVS-1 nt 110 and codon 39 noraml primers and in the second case using the corresponding mutated primers. In both cases the different PCR fragments were visualized. After optimization these primers directed only amplification of their complementary allele. A single blind study was performed on the DNA of 18 individuals who were homozygous or heterozygous for these mutations. In comparison with a parallel investigation, using oligonucleotide probes, all the results were unambiguous. This diagnosis method, which is rapid, easy, direct, and inexpensive, allows the screening of a population group, including heterozygotes, which is required from an epidemiological and anthropological point of view. It could be extended to the large series screening of haplotypes before targeted diagnosis of various genetic diseases

Catecholaminergic polymorphic ventricular tachycardia: RYR2 mutations, bradycardia, and follow up of the patients

Background: The aim of the study was to assess underlying genetic cause(s), clinical features, and response to therapy in catecholaminergic polymorphic ventricular tachycardia (CPVT) probands. Methods and results: We identified 13 missense mutations in the cardiac ryanodine receptor (RYR2) in 12 probands with CPVT. Twelve were new, of which two are de novo mutations. A further 11 patients were silent gene carriers, suggesting that some mutations are associated with low penetrance. A marked resting sinus bradycardia off drugs was observed in all carriers. On ß blocker treatment, 98% of the RYR2 mutation carriers remained symptom free with a median follow up of 2 (range: 2–37) years. Conclusion: CPVT patients with RYR2 mutation have bradycardia regardless of the site of the mutation, which could direct molecular diagnosis in (young) patients without structural heart disease presenting with syncopal events and a slow heart rate but with normal QTc at resting ECG. Treatment with ß blockers has been very effective in our CPVT patients during initial or short term follow up. Given the risk of sudden death and the efficacy of ß blocker therapy, the identification of large numbers of RYR2 mutations thus calls for genetic screening, early diagnosis, and subsequent preventive strategies

Danon's disease as a cause of hypertrophic cardiomyopathy: a systematic survey

Background: Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease caused by mutations in sarcomeric genes. However, extensive genetic screening failed to identify a mutation in about a third of cases. One possible explanation is that other diseases, caused by other genes, may mimic HCM. Objective: To investigate the possible involvement of Danon’s disease, an X linked lysosomal disease, in a large population of patients with HCM. Methods: A population of 197 index cases was considered; 124 were subsequently excluded because of a mutation in sarcomeric genes and 23 because of autosomal dominant inheritance. Fifty index cases were therefore included in molecular analysis (direct sequencing) of the lysosome associated membrane protein 2 (LAMP2) gene responsible for Danon’s disease. Results: Two new mutations leading to premature stop codons were identified in patients who evolved towards severe heart failure (< 25 years old): 657C>T and 173_179del. The prevalence was therefore 1% of the total population (two of 197) or 4% of enrolled index cases (two of 50). Interestingly, Danon’s disease was responsible for half of the cases (two of four) with HCM and clinical skeletal myopathy but was not involved in isolated HCM (none of 41). Conclusions: Danon’s disease may be involved in patients with previously diagnosed as HCM. A diagnosis strategy is proposed. To distinguish HCM from Danon’s disease is important because the clinical evolution, prognosis, mode of inheritance, and therefore genetic counselling are very different

Absence of calsequestrin 2 causes severe forms of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare arrhythmogenic disorder characterized by syncopal events and sudden cardiac death at a young age during physical stress or emotion, in the absence of structural heart disease. We report the first nonsense mutations in the cardiac calsequestrin gene, CASQ2, in three CPVT families. The three mutations, a nonsense R33X, a splicing 532+1 G>A, and a 1-bp deletion, 62delA, are thought to induce premature stop codons. Two patients who experienced syncopes before the age of 7 years were homozygous carriers, suggesting a complete absence of calsequestrin 2. One patient was heterozygous for the stop codon and experienced syncopes from the age of 11 years. Despite the different mutations, there is little phenotypic variation of CPVT for the CASQ2 mutations. Of the 16 heterozygous carriers of these various mutations, 14 were devoid of clinical symptoms or ECG anomalies, whereas 2 of them had ventricular arrhythmias at ECG on exercise tests. In line with this, the diagnosis of the probands was difficult because of the absence of a positive family history. In conclusion, these additional three CASQ2 CPVT families suggest that CASQ2 mutations are more common than previously thought and produce a severe form of CPVT. The full text of this article is available at http://www.circresaha.or

Expanding the phenotype of LMNA mutations in dilated cardiomyopathy and functional consequences of these mutations

Aims: Mutations in the lamin A/C gene (LMNA) have been reported to be involved in dilated cardiomyopathy (DCM) associated with conduction system disease and/or skeletal myopathy. The aim of this study was to perform a mutational analysis of LMNA in a large white population of patients affected by dilated cardiomyopathy with or without associated symptoms. Methods: We performed screening of the coding sequence of LMNA on DNA samples from 66 index cases, and carried out cell transfection experiments to examine the functional consequences of the mutations identified. Results: A new missense (E161K) mutation was identified in a family with early atrial fibrillation and a previously described (R377H) mutation in another family with a quadriceps myopathy associated with DCM. A new mutation (28insA) leading to a premature stop codon was identified in a family affected by DCM with conduction defects. No mutation in LMNA was found in cases with isolated dilated cardiomyopathy. Functional analyses have identified potential physiopathological mechanisms involving identified mutations, such as haploinsufficiency (28insA) or intermediate filament disorganisation (E161K, R377H). Conclusion: For the first time, a specific phenotype characterised by early atrial fibrillation is associated with LMNA mutation. Conversely, mutations in LMNA appear as a rare cause of isolated dilated cardiomyopathy. The variable phenotypes observed in LMNA-DCM might be explained by the variability of functional consequences of LMNA mutations