Twin studies in hypertrophic cardiomyopathy.

The details of three sets of twins, all with hypertrophic cardiomyopathy, are presented. Twins A were monozygotic and concordant and showed haemodynamic evidence of outflow tract obstruc- tion. The lack offamily history suggests a recessive mode of inheritance or a single gene mutation with dominant effect as the cause. Twins B were also monozygotic and concordant, but the rate of progression of their condition was different, one remaining well, the other developing atrial fibrillation and congestive cardiac failure. Twins C were dizygotic, the male member had died suddenly from hypertrophic cardiomyopathy as had his two young sons; the female member and her children are symptomless. The family history suggests a strongly penetrant autosomal domin- ant inheritance. Our observations suggest that hypertrophic cardiomyopathy could sometimes result from a single gene mutation and that the prenatal environment may be important in determining the expression of the gene and the rate of progression of the condition in adult life.