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Type-2 Diabetes Family History Delays the Onset of Type-1 Diabetes

Program for Population Genetics (P.A.Z., H.T., X.X.), Harvard School of Public Health, Boston, Massachusetts 02115; Genetics Research Laboratory (P.A.Z., H.S., G.H., S.T.A.), Chronic Care Center, Beirut, Lebanon; Department of Endocrinology (G.H.), Hôtel-Dieu de France, Beirut, Lebanon; and Division of Endocrinology (S.T.A.), American University of Beirut, Beirut, Lebanon

Address all correspondence and requests for reprints to: Sami T. Azar, M.D., Department of Endocrinology, American University of Beirut, Medical Center, Bliss Street, Beirut, Lebanon. E-mail: . sazar{at}aub.edu.lb

Abstract

Type-1 diabetes (T1D) is an autoimmune disease leading to insulin deficiency. Its occurrence is influenced by genetic and environmental factors. The human leukocyte antigen (HLA) region on chromosome 6 accounts for 45% of the genetic susceptibility for the disease, mainly the HLA-DQB1*0201 and HLA-DQB1*0302 alleles. Among the environmental factors involved, early exposure to cow’s milk seems to be a trigger. In this study, we investigated the occurrence of T1D in 253 Lebanese Caucasian patients, in relation to HLA-DQB1*0201, HLA-DQB1*0302, HLA-DQB1*0602, gender, and early exposure to cow’s milk, as well as to family history of T1D and type-2 diabetes (T2D). Our genetic analysis results show that in the patients studied, 77% and 40% were positive for BQ1*0201 and BQ1*0302, respectively. As for BQ1*0602, only 0.8% of patients were positive for this T1D protective allele, compared with 24% among the controls. Furthermore, our results did not show any gender preference of the disease or any effects of early intake of cow’s milk on the age at onset of T1D. When family history of T2D or T1D was studied, our results show a novel finding whereby an immediate family history of T2D, but not T1D, delays the age at onset of T1D.