APOE2 and consanguinity: A risky combination for Alzheimer's disease

Objective: To investigate the association between APOE genotypes and Alzheimer's disease (AD) in elderly Indian subjects. The study also aims at the identification of consanguinity as disease risk factor for AD. Methods: A total of 100 Indian patients (26 consanguineous, 74 non-consanguineous), meeting criteria for probable or definite AD and 36 cognitively healthy, elderly unrelated control subjects (spouses), were included in the study, The APOE genotyping and statistical analyses (SPSS 7.5) was performed to determine the odds of AD according to APOE genotype. Results: The analysis revealed increased prevalence of E4 allele in patients as compared with controls. The difference in prevalence of E3 and E4 alleles was found to be statistically significant between consanguineous patients and controls as well as non-consanguineous patients and controls. Compared to individuals with the APOE3/3, the odds of having AD were significantly increased among those with one or more copies of the E4 allele, even after adjusting with age and sex. An interesting outcome of the study is the higher prevalence of the E2 allele in consanguineous AD patients (in contrast to previously reported studies). The risk for AD was higher in consanguineous individuals with E2/4 genotype (1.62 fold), as compared to non-consanguineous individuals. Discussion: The Results support that the APOE4 allele plays a role as a risk factor for AD and suggests that the APOE2 allele may not play a protective role in the development of AD in Indians, especially individuals with family history of consanguinity. The study hypothesises that the consanguinity modifies the disease risk associated with E2 allele, although this allele is considered protective. The less number of subjects from a broader population limits the study. The wide-ranging population and ethnicity-based studies in the most inbred groups of the world may provide comprehensive insight into this conclusion.