Familial and sporadic hypertrophic myopathy: differences and similarities in a genotyped population. A long follow-up study

Abstract

Background: Hypertrophic cardiomyopathy (HCM) is a genetic disease associated with mutations in genes encoding cardiac sarcomere proteins. A mutation is identified in two-thirds of cases, and more frequently in familial forms. Doubts remain concerning the true identity of the sporadic form.

Objective: To compare, in a genotyped population, the phenotypic expression of the disease over time in patients with familial and sporadic HCM.

Methods: 79 patients with HCM, aged 39 +/- 17.8 years at diagnosis, were followed for 12 +/- 9.5 (1-30) years and divided into two groups: G1 (familial)--68 patients (24 unrelated index patients, 44 relatives), follow-up time (FUP) 12 +/- 9.8 (1-30) years; G2 (sporadic)1 index patients (no phenotypic disease in first-degree relatives), FUP 10.8 +/- 8 (2-24) years. Fabry disease was excluded in G2. The two groups were compared regarding clinical, ECG and echocardiographic (echo) features at diagnosis and after FUP. Five sarcomere genes (MYH7, MYBPC3, TNNT2, MYL2 and TNNI3) were screened for mutations by direct sequencing, after PCR amplification with intronic sets of oligonucleotide primers designed according to the published genomic sequence of the genes.

Results: A) Thirteen different mutations (in 3 genes) were identified in 14 index patients in G1; only in one patient in G2 was a mutation found. B) The two groups differed clinically in age at diagnosis (G1: 37.18 (4-79) years; G2: 51 +/- 14 (19-67) years; p = 0.02), and family history of sudden cardiac death (G1: 12/24 families; G2: 1/11 families; p = 0.04). Age, gender, FUP, symptoms, need for medical treatment, cardiovascular (CV) hospitalization and mortality (CV or any cause) were similar. C) ECG patterns did not differ, although significant (but similar) changes occurred in 45% (G1) and 36% (G2) of patients (p = 0.75). These changes were in the same direction, with a trend in both groups toward the development of atrial fibrillation and/or advanced conduction disease. D) Echo features (only considered in adults) were similar despite significant changes during FUP (in 68% of G1, and 82% of G2; p = 0.48). These changes also followed the same tendency: progression to a more diffuse pattern of ventricular hypertrophy (G1: 52%; G2: 73%; p = 0.33) and development of left atrial dilatation (G1: 37%; G2: 45%; p = 0.52).

Conclusions: The similar phenotypic expression and behavior over time in familial and sporadic forms of HCM strongly indicate that the disease is one and the same. Differences in genetic findings, age at diagnosis and family history of sudden death suggest that sporadic forms may be caused by low penetrance de novo mutations in sarcomeric genes other than those associated with familial disease.