Genetic evidence of dissociation (generational skips) of electrical from morphologic forms of hypertrophic cardiomyopathy.

The diagnosis of hypertrophic cardiomyopathy (HC) is traditionally based on the demonstration by echocardiography of left ventricular hypertrophy in the absence of apparent cause. This study reports on 5 adults in 4 families who are obligate or highly probable carriers of the HC gene by virtue of their position in the pedigree, but who have normal echocardiographic findings. Four of these 5 patients had abnormal signal-averaged electrocardiograms, a finding suggesting the presence of electrical disease despite the absence of left ventricular hypertrophy. The fifth patient, an identical twin of a patient with familial HC, had neither left ventricular hypertrophy nor a myocardial electrical abnormality. These data indicate that the spectrum of HC includes patients who have a potentially arrhythmogenic left ventricular substrate but who have no evidence of left ventricular hypertrophy. Our data demonstrating generational skips also imply that some instances of HC previously judged to be sporadic may indeed by familial.