Reduced insulin secretion in offspring of African type 2 diabetic parents

OBJECTIVE: To determine the early biochemical predictors of increased susceptibility to develop diabetes in offspring of African type 2 diabetic parents. RESEARCH DESIGN AND METHODS: A total of 69 offspring (case subjects) of 26 families in Cameroon with at least one type 2 diabetic parent were studied, and 62 offspring (control subjects) from 25 families in Cameroon with no parent with type 2 diabetes underwent an oral glucose tolerance test. Early insulin secretion was calculated using the ratio of the 0- to 30-min incremental insulin values to the 0- to 30-min incremental glucose. Anthropometric parameters were also measured. RESULTS: Of the case subjects, 23% were glucose intolerant (4% with diabetes and 19% with impaired glucose tolerance [IGT]) compared with 6.5% (all with IGT) of control subjects (P = 0.02). There was also an increasing prevalence of glucose intolerance, especially IGT with increasing number of glucose-intolerant parents. Fasting serum insulin levels were not different in the two groups; however, at 30 min, the case subjects had lower insulin levels than the control subjects (P < 0.006). Case subjects with IGT had lower 30-min insulin concentration, early insulin secretion, and 2-h insulin levels than those with normal glucose tolerance (NGT) (F = 4.1, P < 0.05; F = 4.1, P < 0.04; and F = 5.1, P < 0.03, respectively). Furthermore, case subjects with NGT and IGT had lower early insulin secretion than control subjects (F = 4. 1, P < 0.03). These differences remained after adjustment for BMI and regardless of the status of parental diabetes. Two-hour insulin concentration showed a positive association (odds ratio = 0.95 CI 0.90-0.99, P = 0.039) with IGT in the case subjects. CONCLUSIONS: Diabetes and IGT are more prevalent in the offspring of African type 2 diabetic parents, and this may be due to an underlying degree of beta-cell impairment marked by reduced early-phase insulin secretion.