Identification of an elusive spliceogenic MYBPC3 variant in an otherwise genotype-negative hypertrophic cardiomyopathy pedigree.

The finding of a genotype-negative hypertrophic cardiomyopathy (HCM) pedigree with several affected members indicating a familial origin of the disease has driven this study to discover causative gene variants. Genetic testing of the proband and subsequent family screening revealed the presence of a rare variant in the MYBPC3 gene, c.3331-26T>G in intron 30, with evidence supporting cosegregation with the disease in the family. An analysis of potential splice-altering activity using several splicing algorithms consistently yielded low scores. Minigene expression analysis at the mRNA and protein levels revealed that c.3331-26T>G is a spliceogenic variant with major splice-altering activity leading to undetectable levels of properly spliced transcripts or the corresponding protein. Minigene and patient mRNA analyses indicated that this variant induces complete and partial retention of intron 30, which was expected to lead to haploinsufficiency in carrier patients. As most spliceogenic MYBPC3 variants, c.3331-26T>G appears to be non-recurrent, since it was identified in only two additional unrelated probands in our large HCM cohort. In fact, the frequency analysis of 46 known splice-altering MYBPC3 intronic nucleotide substitutions in our HCM cohort revealed 9 recurrent and 16 non-recurrent variants present in a few probands (≤ 4), while 21 were not detected. The identification of non-recurrent elusive MYBPC3 spliceogenic variants that escape detection by in silico algorithms represents a challenge for genetic diagnosis of HCM and contributes to solving a fraction of genotype-negative HCM cases.

Screening mutations in myosin binding protein C3 gene in a cohort of patients with Hypertrophic Cardiomyopathy.

BACKGROUND: MyBPC3 mutations are amongst the most frequent causes of hypertrophic cardiomyopathy, however, its prevalence varies between populations. They have been associated with mild and late onset disease expression. Our objectives were to establish the prevalence of MyBPC3 mutations and determine their associated clinical characteristics in our patients. METHODS: Screening by Single Strand Conformation Polymorphisms (SSCP) and sequencing of the fragments with abnormal motility of the MyBPC3 gene in 130 unrelated consecutive HCM index cases. Genotype-Phenotype correlation studies were done in positive families. RESULTS: 16 mutations were found in 20 index cases (15%): 5 novel [D75N, V471E, Q327fs, IVS6+5G>A (homozygous), and IVS11-9G>A] and 11 previously described [A216T, R495W, R502Q (2 families), E542Q (3 families), T957S, R1022P (2 families), E1179K, K504del, K600fs, P955fs and IVS29+5G>A]. Maximum wall thickness and age at time of diagnosis were similar to patients with MYH7 mutations [25(7) vs. 27(8), p = 0.16], [46(16) vs. 44(19), p = 0.9]. CONCLUSIONS: Mutations in MyBPC3 are present in 15% of our hypertrophic cardiomyopathy families. Severe hypertrophy and early expression are compatible with the presence of MyBPC3 mutations. The genetic diagnosis not only allows avoiding clinical follow up of non carriers but it opens new possibilities that includes: to take preventive clinical decisions in mutation carriers than have not developed the disease yet, the establishment of genotype-phenotype relationship, and to establish a genetic diagnosis routine in patients with familial HCM.

[Beta-myosin heavy-chain gene mutations in patients with hypertrophic cardiomyopathy]. / Mutaciones en el gen de la cadena pesada de la betamiosina en pacientes con miocardiopatía hipertrófica.

INTRODUCTION AND OBJECTIVES: To determine the frequency of mutations in the beta-myosin heavy-chain gene (MYH7) in a cohort of patients with hypertrophic cardiomyopathy (HCM) and their families, and to investigate correlations between genotype and phenotype. METHODS: Single-strand conformation polymorphism analysis and sequencing of fragments with abnormal MYH7 gene mobility were carried out in 128 consecutive index patients with HCM. The phenotypes of patients with and without mutations were compared and the phenotypes of identified families were recorded. RESULTS: A total of 11 mutations were found in 13 families (10%); 7/11 had been previously described. The I736T mutation was found in three families and the A797T in two. One patient had two mutations (i.e., I736T and R787H). Mutations were more frequent in patients with a family history of sudden death (31%) and in those with severe hypertrophy (39% had a thickness > or = 30 mm). Mutations were found in 29 of 42 members of the 13 families, including six family members (20%) who were healthy carriers and aged < or = 36 years. Sudden death had occurred in eight members of four families: four in two families with the I736T mutation, one in a family with A797T, one in a family with R870H, and two in a family with A901P. CONCLUSIONS: MYH7 mutations were present in 10% of our families. Mutations were more frequent in patients with a family history of sudden death and in those with severe hypertrophy. Most mutations had been described previously. Some appeared in several families. For some mutations, the correlation between genotype and phenotype was stable, while for others, there were marked differences between the phenotypes of the index patients and their relatives, suggesting the presence of additional genetic factors that have yet to be identified.

Phenotype and prognostic correlations of the converter region mutations affecting the ß myosin heavy chain.

OBJECTIVES: The prognostic value of genetic studies in cardiomyopathies is still controversial. Our objective was to evaluate the outcome of patients with cardiomyopathy with mutations in the converter domain of ß myosin heavy chain (MYH7). METHODS: Clinical characteristics and survival of 117 affected members with mutations in the converter domain of MYH7 were compared with 409 patients described in the literature with mutations in the same region. RESULTS: Twenty-five mutations were evaluated (9 in our families including 3 novel (Ile730Asn, Asp717Gly and Arg719Pro)). Clinical diagnoses were hypertrophic (n=407), dilated (n=15), non-compaction (n=4) and restrictive (n=5) cardiomyopathies, unspecified cardiomyopathy (n=11), sudden death (n=50) and 35 healthy carriers. One hundred eighty-four had events (cardiovascular death or transplant). Median event-free survival was 50±2 years in our patients and 53±3 years in the literature (p=0.27). There were significant differences in the outcome between mutation: Ile736Thr had fewer events than other mutations in the region (p=0.01), while Arg719Gln (p<0.01) had reduced event-free survival. CONCLUSIONS: Mutations in the converter region are generally associated with adverse prognosis although there are differences between mutations. The identification of a mutation in this particular region provides important prognostic information that should be considered in the clinical management of affected patients.

Mutation in the alpha-cardiac actin gene associated with apical hypertrophic cardiomyopathy, left ventricular non-compaction, and septal defects.

AIMS: The E101K mutation in the alpha-cardiac actin gene (ACTC) has been associated with apical hypertrophic cardiomyopathy (HCM). As prominent trabeculations were described in some carriers, we screened for the E101K mutation in our index patients with HCM, dilated cardiomyopathy (DCM), or left ventricular non-compaction (LVNC). METHODS AND RESULTS: Clinical, echocardiographic, and genetic screening by restriction fragment length polymorphism of the ACTC E101K mutation in 247 families with HCM, DCM, or LVNC. The mutation was found in five index patients (one with LVNC and four with HCM). Clinical and morphological data were obtained from 94 family members. Forty-six individuals had cardiomyopathy (43 with the mutation and three with no genetic study): 23 fulfilled criteria for LVNC, 22 were diagnosed as apical HCM, and one had been diagnosed as restrictive cardiomyopathy. There had been one heart transplant and one congestive heart failure death in patients with severe diastolic dysfunction, and five premature sudden deaths. The E101K mutation was not found in 48 unaffected relatives. Septal defects (eight atrial and one ventricular) were found in nine mutant carriers from four families, and were absent in relatives without the mutation (P = 0.003). CONCLUSION: LVNC and HCM may appear as overlapping entities. The ACTC E101K mutation should be considered in the genetic diagnosis of LVNC, apical HCM, and septal defects.