Concordance rate for Type II diabetes mellitus in monozygotic twins: actuarial analysis

To determine the concordance rate for Type II (non-insulin-dependent) diabe tes mellitus in monozygotic twin pairs, initially ascertained discordant fo r diabetes, we carried out a prospective study on 44 non-diabetic subjects, each of whom had a sibling twin with diabetes (21 men, 23 women, median ag e 55 years, interquartile range 47-65). The subjects were referred as disco rdant for Type II diabetes. The twin pairs were part of the British Diabeti c Twin Study and ascertained between May 1968 and January 1998. These subje cts underwent an OGTT at time of referral and periodically thereafter. The mean follow-up was 8 years (range 0-18 years) and data were collected until January 1996. The percentage of twins who developed Type II diabetes was a ssessed by standard actuarial life-table methods and the pairwise concordan ce rate, that is the proportion of concordant pairs over the sum of concord ant and discordant pairs, was calculated. The observed rates of concordance for Type II diabetes at 1, 5, 10, and 15 years follow-up were 17, 33, 57, and 76%, respectively. The concordance rate for any abnormality of glucose metabolism (either Type II diabetes or impaired glucose tolerance) at 15 ye ars follow-up was 96%. The concordance rate for Type II diabetes in monozyg otic twins is very high even in twins initially ascertained discordant for diabetes.