Alzheimer's disease and type 2 diabetes: the association study of polymorphisms in tumor necrosis factor-alpha and apolipoprotein E genes

Type 2 diabetes (T2D) and Alzheimer's disease (AD) are two progressive disorders with high prevalence worldwide. Polymorphisms in tumor necrosis factor-alpha (TNF-alpha) and apolipoprotein E (ApoE) genes might be associated with both T2D and AD, representing possible genetic markers for the development of the AD in subjects with T2D. The aim was to determine ApoE and G-308A TNF-alpha gene polymorphisms in unrelated Croatian Caucasians: 207 patients with sporadic AD, 196 T2D patients and 456 healthy controls. Patients with AD had higher frequency of ApoE4 allele compared to T2D patients and controls. The significant association, observed between ApoE2 allele and T2D, disappeared after the data were adjusted for age and sex. The genotype or allele frequencies of G-308A TNF-alpha gene polymorphism were similar among the patients with AD, T2D and healthy controls. In conclusion, these results do not support the hypothesis that the A allele of G-308A TNF-alpha gene polymorphism is associated either with AD or T2D. Our data confirm the association between the ApoE4 allele and AD, and point out the E2 allele of ApoE gene as the possible risk factor for T2D.