Twin studies in medical research.

SIR,-Dr Phillips questions (April 17, p 1008) the value of twin studies in estimating the genetic component in the most common diseases of adult life. He points out that the intrauterine environment of twins, monozygous as well as dizygous, may be different and that this distinction may account for later differences in disease prevalence between co-twins. Thus, a greater concordance between monozygotic than dizygotic twins does not, Phillips says, necessarily indicate a genetic basis for a disease. We have long been studying diabetes, one of the adult diseases that Phillips mentions, and we offer our comments with respect to this disease.