Does zygosity influence the metabolic profile of twins? A population based cross sectional study.

OBJECTIVE To study the influence of zygosity on the metabolic variables involved in the pathophysiology of type 2 diabetes. DESIGN Population based cross sectional study. SETTING Odense University Hospital, Denmark. PARTICIPANTS 125 monozygotic twin pairs and 178 dizygotic twin pairs of the same sex born between 1921 and 1940. MAIN OUTCOME MEASURES Clinical characteristics of monozygotic and dizygotic twins with or without a family history of type 2 diabetes. RESULTS Absolute prevalences of type 2 diabetes and impaired glucose tolerance according to the World Health Organisation criteria were similar in both the monozygotic and the dizygotic twins as were measurements of height, weight, body mass index, waist to hip ratio, and fasting plasma glucose and insulin concentrations. During the oral glucose tolerance test, monozygotic twins had a higher incremental plasma insulin area under the curve than dizygotic twins (10.05 (SD 0.68) v 9.89 (0.72) pmol/lxminutes, P<0.01) indicating insulin resistance. In twins with normal glucose tolerance and without first degree relatives or co-twins with type 2 diabetes or impaired glucose tolerance, both the glucose and insulin areas under the curve were higher among monozygotic twins (glucose 214.4 (88.3) v 189.8 (78.4) mmol/lxminutes, P<0.05; insulin 20 040 (14 865-32 554) v 17 625 (12 330-23 640) pmol/lxminutes, P=0.08). CONCLUSION Zygosity influences both plasma glucose and plasma insulin concentrations during an oral glucose tolerance test. This supports an intrauterine influence on glucose homeostasis and perhaps on insulin resistance in humans.