Formin Homology 2 Domain Containing 3 (FHOD3) Is a Genetic Basis for Hypertrophic Cardiomyopathy.

BACKGROUND: The genetic cause of hypertrophic cardiomyopathy remains unexplained in a substantial proportion of cases. Formin homology 2 domain containing 3 (FHOD3) may have a role in the pathogenesis of cardiac hypertrophy but has not been implicated in hypertrophic cardiomyopathy. OBJECTIVES: This study sought to investigate the relation between FHOD3 mutations and the development of hypertrophic cardiomyopathy. METHODS: FHOD3 was sequenced by massive parallel sequencing in 3,189 hypertrophic cardiomyopathy unrelated probands and 2,777 patients with no evidence of cardiomyopathy (disease control subjects). The authors evaluated protein-altering candidate variants in FHOD3 for cosegregation, clinical characteristics, and outcomes. RESULTS: The authors identified 94 candidate variants in 132 probands. The variants' frequencies were significantly higher in patients with hypertrophic cardiomyopathy (74 of 3,189 [2.32%]) than in disease control subjects (18 of 2,777 [0.65%]; p < 0.001) or in the gnomAD database (1,049 of 138,606 [0.76%]; p < 0.001). FHOD3 mutations cosegregated with hypertrophic cardiomyopathy in 17 families, with a combined logarithm of the odds score of 7.92, indicative of very strong segregation. One-half of the disease-causing variants were clustered in a small conserved coiled-coil domain (amino acids 622 to 655); odds ratio for hypertrophic cardiomyopathy was 21.8 versus disease control subjects (95% confidence interval: 1.3 to 37.9; p < 0.001) and 14.1 against gnomAD (95% confidence interval: 6.9 to 28.7; p < 0.001). Hypertrophic cardiomyopathy patients carrying (likely) pathogenic mutations in FHOD3 (n = 70) were diagnosed after age 30 years (mean 46.1 ± 18.7 years), and two-thirds (66%) were males. Of the patients, 82% had asymmetric septal hypertrophy (mean 18.8 ± 5 mm); left ventricular ejection fraction <50% was present in 14% and hypertrabeculation in 16%. Events were rare before age 30 years, with an annual cardiovascular death incidence of 1% during follow-up. CONCLUSIONS: FHOD3 is a novel disease gene in hypertrophic cardiomyopathy, accounting for approximately 1% to 2% of cases. The phenotype and the rate of cardiovascular events are similar to those reported in unselected cohorts. The FHOD3 gene should be routinely included in hypertrophic cardiomyopathy genetic testing panels.

Phenotypic Characterization of a Family With An In-frame Deletion in the DMD Gene and Variable Penetrance.

Duchenne muscular dystrophy is a disorder with variable expression caused by framedisrupting mutations in the dystrophin gene. It is characterized by progressive muscle weakness and dilated cardiomyopathy. In-frame dystrophin mutations cause a clinically moderate disorder named Becker muscular dystrophy. Our aim was to study the clinical and genetic characteristics of a family with inherited cardiomyopathy and Becker muscular dystrophy. The index case was diagnosed with psychomotor retardation at 5 years of age. Asymmetric left ventricular hypertrophy and a long QT interval were evidenced at the age of 12. Mild muscular weakness was developed subsequently. Three genetic variants were identified in the index case: p.Arg891Alafs*160 in the MYBPC3 gene, p.Thr263Met in the KCNJ5 gene, and p.Ser2437_Ile2554delinsPhe in the DMD gene. The latter was expected to generate an in-frame deletion of exons 51 and 52 of the dystrophin gene. A family study revealed that the father and 3 uncles were carriers of the MYBPC3 mutation. The mother and a maternal grandfather were carriers of the other 2 variants. The 80-year-old grandfather, who had the dystrophin mutation, showed no sign of cardiomyopathy or muscular weakness. The deletion of exons 51 and 52 in the DMD gene, which has been proposed as one of the therapeutic strategies for Duchenne, is consistent with a normal life expectancy and the absence of myopathic symptoms in hemizygous males.

Factors Influencing the Phenotypic Expression of Hypertrophic Cardiomyopathy in Genetic Carriers.

INTRODUCTION AND OBJECTIVES: Hypertrophic cardiomyopathy (HCM) is a disorder with variable expression. It is mainly caused by mutations in sarcomeric genes but the phenotype could be modulated by other factors. The aim of this study was to determine whether factors such as sex, systemic hypertension, or physical activity are modifiers of disease severity and to establish their role in age-related penetrance of HCM. METHODS: We evaluated 272 individuals (mean age 49 ± 17 years, 57% males) from 72 families with causative mutations. The relationship between sex, hypertension, physical activity, and left ventricular hypertrophy was studied. RESULTS: The proportion of affected individuals increased with age. Men developed the disease 12.5 years earlier than women (adjusted median, 95%CI, -17.52 to -6.48; P < .001). Hypertensive patients were diagnosed with HCM later (10.8 years of delay) than normotensive patients (adjusted median, 95%CI, 6.28-17.09; P < .001). Individuals who performed physical activity were diagnosed with HCM significantly earlier (7.3 years, adjusted median, 95%CI, -14.49 to -1.51; P = .016). Sex, hypertension, and the degree of physical activity were not significantly associated with the severity of left ventricular hypertrophy. Adjusted survival both free from sudden death and from the combined event were not influenced by any of the exploratory variables. CONCLUSIONS: Men and athletes who are carriers of sarcomeric mutations are diagnosed earlier than women and sedentary individuals. Hypertensive carriers of sarcomeric mutations have a delayed diagnosis. Sex, hypertension, and physical activity are not associated with disease severity in carriers of HCM causative mutations.

A Novel Founder Mutation in MYBPC3: Phenotypic Comparison With the Most Prevalent MYBPC3 Mutation in Spain.

INTRODUCTION AND OBJECTIVES: Mutations in MYBPC3 are the cause of hypertrophic cardiomyopathy (HCM). Although most lead to a truncating protein, the severity of the phenotype differs. We describe the clinical phenotype of a novel MYBPC3 mutation, p.Pro108Alafs*9, present in 13 families from southern Spain and compare it with the most prevalent MYBPC3 mutation in this region (c.2308+1 G>A). METHODS: We studied 107 relatives of 13 index cases diagnosed as HCM carriers of the p.Pro108Alafs*9 mutation. Pedigree analysis, clinical evaluation, and genotyping were performed. RESULTS: A total of 54 carriers of p.Pro108Alafs*9 were identified, of whom 39 had HCM. There were 5 cases of sudden death in the 13 families. Disease penetrance was greater as age increased and HCM patients were more frequently male and developed disease earlier than female patients. The phenotype was similar in p.Pro108Alafs*9 and in c.2308+1 G>A, but differences were found in several risk factors and in survival. There was a trend toward a higher left ventricular mass in p.Pro108Alafs*9 vs c.2308+1G>A. Cardiac magnetic resonance revealed a similar extent and pattern of fibrosis. CONCLUSIONS: The p.Pro108Alafs*9 mutation is associated with HCM, high penetrance, and disease onset in middle age.

Hypertrophic cardiomyopathy. A study of the troponin-T gene in 127 Spanish families.

The information available on the correlation between genotype and phenotype and the prognostic implications of different troponin-T gene mutations is sparse and, at times, contradictory. We studied the TNNT2 gene in 127 patients with hypertrophic cardiomyopathy and identified three mutations in patients from four families (3.1%): the Phe87Leu mutation, which has not been previously reported, the Arg278Cys mutation (two families) and the Asp271Ile mutation. Seven carriers of the Phe87Leu mutation (aged 29 to 52 years) were found to have mild hypertrophy (i.e., a wall thickness <16 mm). There were 11 deaths associated with the condition (seven sudden deaths), and four of those who died were aged between 14 and 16 years. No sudden deaths occurred in the other three families. In conclusion, troponin-T mutations were responsible for 3% of the hypertrophic cardiomyopathy cases in our study population. The Phe87Leu mutation was associated with only mild hypertrophy but with a high risk of sudden death.