Importance of family history in type 2 black South African diabetic patients

Objective - To assess the family history of diabetes in type 2 black South African diabetics with emphasis on the parental phenotype. Design - Prospective case-control study in which family histories were obtained from patients. Setting - Diabetic clinic of a provincial teaching hospital in the Transkei region of South Africa. Subjects - A total of 1111 type 2 diabetics attending the diabetic clinic and 687 controls. Main outcome measures - History of diabetes in parents, siblings, maternal and paternal grandparents, aunts, and uncles. Results - Altogether 27.3% of diabetic subjects had a family history of diabetes compared with 8.4% in the control group (p<0.01). Among the group with positive family history 82.6% reported only one diabetic family member, while 17.4% reported at least two relatives; 6.6% had a diabetic relative from both maternal and paternal sides, and 87.8% had first degree relative with diabetes. Among them there was a significant maternal aggregation with 64.7% of patients having a diabetic mother compared with 27% who had a diabetic father (p<0.01). No maternal effect was observed among the second and third degree relatives. Patients with positive family history had an earlier onset of diabetes than those without family history (p<0.01). Conclusion - These data suggest that type 2 diabetes is heritable in black South African diabetics. It is also likely that maternal influences may play an important part.