GENOTYPE-PHENOTYPE CORRELATIONS IN HYPERTROPHIC CARDIOMYOPATHY - INSIGHTS PROVIDED BY COMPARISONS OF KINDREDS WITH DISTINCT AND IDENTICAL BETA-MYOSIN HEAVY-CHAIN GENE-MUTATIONS

Background We have previously described two distinct mutations in the beta-myosin heavy chain gene with markedly different clinical presentations and outcome: The 908(Leu-->Val) mutation was associated with a low disease penetrance and a benign prognosis. In contrast, the 403(Arg-->Gln) mutation in a Caucasian kindred was associated with a 100% disease penetrance and high incidence of sudden cardiac death. Recently, another mutation, 606(Val-->Met), has been reported to be associated with ''near normal survival'' and offered as evidence for the benign nature of neutral charge substitutions. Methods and Results We report (1) a large kindred (245 family members at risk of inheriting the disease gene) with a 256(Gly-->Glu) mutation characterized by a similar disease penetrance in adults and in children (56% and 60%, respectively) and a cumulative sudden cardiac death rate of only 2% at 50 years of age, (2) a kindred with the 606(Val-->Met) mutation with four sudden cardiac deaths in eight affected individuals, and (3) a Korean kindred with the 403(Arg-->Gln) mutation. Although the disease occurred early and was associated with a high prevalence of myocardial ischemia in both of our kindreds with the 403(Arg-->Gln) mutation, no sudden cardiac death or syncope has occurred in the Korean kindred. Furthermore, in the Caucasian kindred, all patients had nonobstructive hypertrophic cardiomyopathy, but most of the patients in the Korean kindred bed left ventricular outflow obstruction. Conclusions The conclusions are as follows: (1) Although several sudden cardiac deaths are sufficient to establish that a mutation is malignant, study of a large kindred is necessary to be certain that a mutation is benign. To date, only the 908(Leu-->Val) and the 256(Gly-->Glu) mutations satisfy this requirement. (2) The 256(Gly-->Glu) mutation demonstrates that not ail mutations that result in a charge change are malignant. (3) Conversely, the 606(Val-->Met) mutation is malignant in some kindreds; hence, despite the absence of a charge change, minor substitutions in critical regions of beta-myosin heavy chain protein may also have serious consequences. (4) The diverse ethnic origins of the two 403(Arg-->Gln) kindreds provide evidence suggesting that the identical mutation occurred independently and was associated with different genetic backgrounds. Their distinct phenotypes underline the importance of modifying genes and nongenetic factors.