No evidence of a higher 10 year period prevalence of diabetes among 77,885 twins compared with 215,264 singletons from the Danish birth cohorts 1910-1989.

AIMS/HYPOTHESIS: Previous Danish twin studies have found a highly increased risk of precursors of type 2 diabetes as well as a higher prevalence of type 2 diabetes among twins compared with singletons. Likewise, small-scale studies of Danish twins have shown that monozygotic twins have a higher risk of developing precursors of type 2 diabetes compared with dizygotic twins. In the present register-based study, the 10 year period diabetes prevalence in Danish twins is compared with that in a random sample of Danish citizens. Furthermore, the 10 year period prevalence of diabetes in monozygotic twins is compared with that in dizygotic twins.

METHODS

The study population consisted of twins (n = 77,885) identified in the Danish Twin Registry, and a 5% random sample (n = 215,264) from the birth cohorts 1910-1989. We identified diabetes patients by means of three nationwide Danish health registers.

RESULTS

The number of identified diabetes cases among males was 6,677 (6.24%) for singletons vs 2,271 (5.68%) for twins (difference = 0.56% [0.29-0.83%]). The number among females was 6,143 (5.67%) for singletons and 1,722 (4.54%) for twins (difference = 1.13% [0.88-0.38%]). Restriction to various birth cohorts, known zygosity and known type 2 diabetes did not alter the overall conclusions. The difference between monozygotic twins (males, 5.29%; females, 4.40%) and dizygotic twins (males, 5.77%; females, 4.63%) was non-significant.

CONCLUSIONS/INTERPRETATION: Danish twins do not have an increased risk of developing diabetes compared with singletons, and the risk of diabetes among monozygotic twins does not differ from that of dizygotic twins.