Rheumatic Heart Disease in Identical Twins

It has long been recognized that acute rheumatism and rheumatic heart disease occur more frequently in some families than in others. It is, however, far from clear whether this increased incidence is due to genetic factors or to exposure to the same environment. Roberts and Thomson (1934) considered that the most reasonable explanation of the family incidence of the disease was that it is due to genetically determined differences in susceptibility, but that environmental factors are necessary for the disease to become manifest in susceptible individuals. They considered that although their study reveals a strong familial tendency to the disease, the findings were not sufficiently definite to determine the relative importance of heredity and environment. In view of this doubt the study of rheumatic heart disease in identical twins may be of value. Morgan and Webster (1938) have already reported mitral stenosis developing after rheumatic fever in identical twins, one of whom died at the age of twenty-three from the disease.