Assessment of the heritability of different aspects of betacell function in normoglycaemic monozygotic and dizygotic twins

Methods

From the Netherlands Twin Register 77 twin family's are recruited, including  51 Monozygotic  pairs (21 male), 21 Dizygotic  pairs (8 male), 5 incomplete twinpairs (3 male) and 31 same sex siblings. They were all healhy, 20 to 50 years old and of caucasian origin.The study protocol consisted of one home screening visit to exclude diabetes mellitus by a 75-g oral glucose tolerance test . After inclusion, the participants came  to the clinical research unit  for a mixed meal test. At a later stage 2/3 of the subjects came to the clinic once again to undergo a combined euglycaemic hyperinsulinaemic and a modified hyperglycaemic clamp test, being the gold standard tests for insulin sensitivity and insulin secretion, respectively. The following variables have been recorded: birth weight, medical history, family history of Diabetes Mellitus, life style questionnaires, eating habits questionnaires and a physical examination  including anthropometrical measurements, respiration rate, bloodpressure and pulse rate. Blood samples are obtained for, among others, determination of glucose, insulin, pro-insulin, C-peptide and incretins.
Laboratory  analyses were  performed at the Vu University Medical Centre (department of Clinical Chemistry and endocrinology) for HbA1c and 
some hormonal levels. Serum was also stored at -80 degrees for analysis in due course.
Data-analysis did start and will be continued with stuctural equation modelling in Mx.