Pascale Richard

Hypertrophic Cardiomyopathy Distribution of Disease Genes, Spectrum of Mutations, and Implications for a Molecular Diagnosis Strategy

Background—Hypertrophic cardiomyopathy is an autosomal-dominant disorder in which 10 genes and numerous mutations have been reported. The aim of the present study was to perform a systematic screening of these genes in a large population, to evaluate the distribution of the disease genes, and to determine the best molecular strategy in clinical practice. Methods and Results—The entire coding sequences of 9 genes (MYH7, MYBPC3, TNNI3, TNNT2, MYL2, MYL3, TPM1, ACTC, and TNNC1) were analyzed in 197 unrelated index cases with familial or sporadic hypertrophic cardiomyopathy. Disease-causing mutations were identified in 124 index patients (≈63%), and 97 different mutations, including 60 novel ones, were identified. The cardiac myosin-binding protein C (MYBPC3) and &bgr;-myosin heavy chain (MYH7) genes accounted for 82% of families with identified mutations (42% and 40%, respectively). Distribution of the genes varied according to the prognosis (P =0.036). Moreover, a mutation was found in 15 of 25 index cases with “sporadic” hypertrophic cardiomyopathy (60%). Finally, 6 families had patients with more than one mutation, and phenotype analyses suggested a gene dose effect in these compound-heterozygous, double-heterozygous, or homozygous patients. Conclusion—These results might have implications for genetic diagnosis strategy and, subsequently, for genetic counseling. First, on the basis of this experience, the screening of already known mutations is not helpful. The analysis should start by testing MYBPC3 and MYH7 and then focus on TNNI3, TNNT2, and MYL2. Second, in particularly severe phenotypes, several mutations should be searched. Finally, sporadic cases can be successfully screened.

Clinical Features and Prognostic Implications of Familial Hypertrophic Cardiomyopathy Related to the Cardiac Myosin-Binding Protein C Gene

BACKGROUND Little information is available on phenotype-genotype correlations in familial hypertrophic cardiomyopathy that are related to the cardiac myosin binding protein C (MYBPC3) gene. The aim of this study was to perform this type of analysis. METHODS AND RESULTS We studied 76 genetically affected subjects from nine families with seven recently identified mutations (SASint20, SDSint7, SDSint23, branch point int23, Glu542Gln, a deletion in exon 25, and a duplication/deletion in exon 33) in the MYBPC3 gene. Detailed clinical, ECG, and echocardiographic parameters were analyzed. An intergene analysis was performed by comparing the MYBPC3 group to seven mutations in the beta-myosin heavy-chain gene (beta-MHC) group (n=52). There was no significant phenotypic difference among the different mutations in the MYBPC3 gene. However, in the MYBPC3 group compared with the beta-MHC group, (1) prognosis was significantly better (P<0.0001), and no deaths occurred before the age of 40 years; (2) the age at onset of symptoms was delayed (41+/-19 versus 35+/-17 years, P<0.002); and (3) before 30 years of age, the phenotype was particularly mild because penetrance was low (41% versus 62%), maximal wall thicknesses lower (12+/-4 versus 16+/-7 mm, P<0.03), and abnormal T waves less frequent (9% versus 45%, P<0.02). CONCLUSIONS These results are consistent with specific clinical features related to the MYBPC3 gene: onset of the disease appears delayed and the prognosis is better than that associated with the beta-MHC gene. These findings could be particularly important for the purpose of clinical management and genetic counseling in familial hypertrophic cardiomyopathy.

De novo LMNA mutations cause a new form of congenital muscular dystrophy

To describe a new entity of congenital muscular dystrophies caused by de novo LMNA mutations.

Desmin-related myopathy with Mallory body-like inclusions is caused by mutations of the selenoprotein N gene.

Desmin‐related myopathies (DRMs) are a heterogeneous group of muscle disorders, morphologically defined by intrasarcoplasmic aggregates of desmin. Mutations in the desmin and the α‐B crystallin genes account for approximately one third of the DRM cases. The genetic basis of the other forms remain unknown, including the early‐onset, recessive form with Mallory body–like inclusions (MB‐DRMs), first described in five related German patients. Recently, we identified the selenoprotein N gene (SEPN1) as responsible for SEPN‐related myopathy (SEPN‐RM), a unique early‐onset myopathy formerly divided in two different nosological categories: rigid spine muscular dystrophy and the severe form of classical multiminicore disease. The finding of Mallory body–like inclusions in two cases of genetically documented SEPN‐RM led us to suspect a relationship between MB‐DRM and SEPN1. In the original MB‐DRM German family, we demonstrated a linkage of the disease to the SEPN1 locus (1p36), and subsequently a homozygous SEPN1 deletion (del 92 nucleotide −19/+73) in the affected patients. A comparative reevaluation showed that MB‐DRM and SEPN‐RM share identical clinical features. Therefore, we propose that MB‐DRM should be categorized as SEPN‐RM. These findings substantiate the molecular heterogeneity of DRM, expand the morphological spectrum of SEPN‐RM, and implicate a necessary reassessment of the nosological boundaries in early‐onset myopathies. Ann Neurol 2004

Diagnostic value of electrocardiography and echocardiography for familial hypertrophic cardiomyopathy in a genotyped adult population.

BACKGROUND The diagnostic value of ECG and echocardiography for familial hypertrophic cardiomyopathy (FHC) has not been reassessed since the development of molecular genetics. The aim of the study was to evaluate it in adults, with the genetic status used as the criterion of reference. METHODS AND RESULTS Ten families with previously identified mutations were studied (9 mutations in 3 genes). ECG and echocardiography were analyzed in 155 adults, of whom 77 were genetically affected and 78 unaffected. The major diagnostic criteria were, for echocardiography, a left ventricular wall thickness > 13 mm and, for ECG, abnormal Q waves, left ventricular hypertrophy, and marked ST-T changes. Minor ECG and echographic abnormalities were also analyzed. (1) Sensitivity and specificity of major criteria were 61% and 97% for ECG and 62% and 100% for echocardiography. (2) Sensitivity but not specificity was age related (from 50% at < 30 years to 94% at > 50 years old, P < .01) and sex related (83% in men versus 57% in women, P = .01). (3) Sensitivity was improved by the addition of minor criteria and by the association of ECG and echocardiography. The negative predictive value was therefore very good (95%) at > 30 years of age. (4) Healthy carriers without any ECG or echocardiographic abnormality represented 17% of genetically affected adults. CONCLUSIONS ECG and echocardiography have similar diagnostic values for FHC in adults, with an excellent specificity and a lower sensitivity. The association of the two techniques allows a better evaluation of the risk of being genetically affected in families with hypertrophic cardiomyopathy.

Identification of an Agrin Mutation that Causes Congenital Myasthenia and Affects Synapse Function

We report the case of a congenital myasthenic syndrome due to a mutation in AGRN, the gene encoding agrin, an extracellular matrix molecule released by the nerve and critical for formation of the neuromuscular junction. Gene analysis identified a homozygous missense mutation, c.5125G>C, leading to the p.Gly1709Arg variant. The muscle-biopsy specimen showed a major disorganization of the neuromuscular junction, including changes in the nerve-terminal cytoskeleton and fragmentation of the synaptic gutters. Experiments performed in nonmuscle cells or in cultured C2C12 myotubes and using recombinant mini-agrin for the mutated and the wild-type forms showed that the mutated form did not impair the activation of MuSK or change the total number of induced acetylcholine receptor aggregates. A solid-phase assay using the dystrophin glycoprotein complex showed that the mutation did not affect the binding of agrin to alpha-dystroglycan. Injection of wild-type or mutated agrin into rat soleus muscle induced the formation of nonsynaptic acetylcholine receptor clusters, but the mutant protein specifically destabilized the endogenous neuromuscular junctions. Importantly, the changes observed in rat muscle injected with mutant agrin recapitulated the pre- and post-synaptic modifications observed in the patient. These results indicate that the mutation does not interfere with the ability of agrin to induce postsynaptic structures but that it dramatically perturbs the maintenance of the neuromuscular junction.

Novel mutations in KvLQT1 that affect Iks activation through interactions with Isk

OBJECTIVES We report the functional expression of four KCNQ1 mutations affecting arginine residues and resulting in Romano-Ward (RW) and the Jervell and Lange-Nielsen (JLN) congenital long QT syndromes. RESULTS The R539W and R190Q mutations were found in typical RW families with an autosomal dominant transmission. The R243H mutation was found in a compound heterozygous JLN patient who presents with deafness and cardiac symptoms. The fourth mutation, R533W, was a new case of recessive form of the RW syndrome since homozygous carriers experienced syncopes but showed no deafness, whereas the heterozygous carriers were asymptomatic. The R190Q mutation failed to produce functional homomeric channels. The R243H, R533W and R539W mutations induced a positive voltage shift of the channel activation but only when co-expressed with IsK, pointing out the critical role of these positively charged residues in the modulation of the gating properties of KvLQT1 by IsK. The positive shift induced by R533W was merely 15%. This small effect was compatible with the recessive character of the RW phenotype transmission. The average QTc was significantly longer (P < 0.01) in patients carrying mutations inducing a total loss of channel function and those patients were also prone to cardiac adverse symptoms (whether syncopes or sudden death) to a greater extent (62 vs. 21%, P < 0.001). CONCLUSIONS Novel mutations are described that induce a voltage shift of the channel activation only in the presence of IsK. They appear associated with a milder cardiac phenotype.

Genomic Organization of the KCNQ1 K+ Channel Gene and Identification of C-Terminal Mutations in the Long-QT Syndrome

The voltage-gated K+ channel KVLQT1 is essential for the repolarization phase of the cardiac action potential and for K+ homeostasis in the inner ear. Mutations in the human KCNQ1 gene encoding the alpha subunit of the KVLQT1 channel cause the long-QT syndrome (LQTS). The autosomal dominant form of this cardiac disease, the Romano-Ward syndrome, is characterized by a prolongation of the QT interval, ventricular arrhythmias, and sudden death. The autosomal recessive form, the Jervell and Lange-Nielsen syndrome, also includes bilateral deafness. In the present study, we report the entire genomic structure of KCNQ1, which consists of 19 exons spanning 400 kb on chromosome 11p15.5. We describe the sequences of exon-intron boundaries and oligonucleotide primers that allow polymerase chain reaction (PCR) amplification of exons from genomic DNA. Two new (CA)n repeat microsatellites were found in introns 10 and 14. The present study provides helpful tools for the linkage analysis and mutation screening of the complete KCNQ1 gene. By use of these tools, five novel mutations were identified in LQTS patients by PCR-single-strand conformational polymorphism (SSCP) analysis in the C-terminal part of KCNQ1: two missense mutations, a 20-bp and 1-bp deletions, and a 1-bp insertion. Such mutations in the C-terminal domain of the gene may be more frequent than previously expected, because this region has not been analyzed so far. This could explain the low percentage of mutations found in large LQTS cohorts.

Codon 102 of the Cardiac Troponin T Gene Is a Putative Hot Spot for Mutations in Familial Hypertrophic Cardiomyopathy

BACKGROUND Familial hypertrophic cardiomyopathy is a phenotypically and genetically heterogeneous disease. In some families, the disease is linked to the CMH2 locus on chromosome 1q3, in which the cardiac troponin T gene (TNNT2) has been identified as the disease gene. The mutations found in this gene appear to be associated with incomplete penetrance and poor prognosis. Because mutational hot spots offer unique possibilities for analysis of genotype-phenotype correlations, new missense mutations that could define such hot spots in TNNT2 were looked for in unrelated French families with familial hypertrophic cardiomyopathy. METHODS AND RESULTS Family members were genotyped with microsatellite markers to detect linkage to the four known disease loci. In family 715, analyses showed linkage to CMH2 only. To accurately position potential mutations on TNNT2, its partial genomic organization was established. Screening for mutations was performed by single-strand conformation polymorphism analysis and sequencing. A new missense mutation, Arg102Leu, was identified in affected members of family 715 because of a G-->T transversion located in the 10th exon of the gene. Penetrance of this new mutation is complete; echocardiographic data show a wide range of hypertrophy; and there was no sudden cardiac death in this family. CONCLUSIONS The codon 102 of the TNNT2 gene is a putative mutational hot spot in familial hypertrophic cardiomyopathy and is associated with phenotypic variability. Analysis of more pedigrees carrying mutations in this codon is necessary to better characterize the clinical and prognostic implications of TNNT2 mutations.

Genetic advances in sarcomeric cardiomyopathies: state of the art

Genetic studies in the 1980s and 1990s led to landmark discoveries that sarcomere mutations cause both hypertrophic and dilated cardiomyopathies. Sarcomere mutations also likely play a role in more complex phenotypes and overlap cardiomyopathies with features of hypertrophy, dilation, diastolic abnormalities, and non-compaction. Identification of the genetic cause of these important conditions provides unique opportunities to interrogate and characterize disease pathogenesis and pathophysiology, starting from the molecular level and expanding from there. With such insights, there is potential for clinical translation that may transform management of patients and families with inherited cardiomyopathies. If key pathways for disease development can be identified, they could potentially serve as targets for novel disease-modifying or disease-preventing therapies. By utilizing gene-based diagnostic testing, we can identify at-risk individuals prior to the onset of clinical disease, allowing for disease-modifying therapy to be initiated early in life, at a time that such treatment may be most successful. In this section, we review the current application of genetics in clinical management, focusing on hypertrophic cardiomyopathy as a paradigm; discuss state-of-the-art genetic testing technology; review emerging knowledge of gene expression in sarcomeric cardiomyopathies; and discuss both the prospects, as well as the challenges, of bringing genetics to medicine.