The apolipoprotein E (APOE) genotype in a Turkish population with Alzheimer's disease

Abstract

Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Three genes are known that, when mutated, cause early-onset AD: β-amyloid precursor protein (APP) gene, presenilin-1 (PS1) gene and pre-senilin-2 (PS2) gene. The majority of AD cases, however, are late-onset and sporadic, occuring in families in whom the inheritance pattern is unclear. This suggests a complex interaction of genetic and environmental factors underlying the etiology of the disease. The Apolipoprotein E (ApoE)-E4 allele is the most common genetic determinant of susceptibility to late-onset AD (LOAD). The objective of this study was to determine the frequency of the three common ApoE alleles in a Turkish population with AD, in comparison with non AD elderly controls. One thousand and seventeen randomly selected individuals over the age of 70 years were screened with a validated Turkish version of the Mini Mental Status Examination (MMSE), and 281 selected subjects underwent detailed clinical examination. Of these, 57 were diagnosed as probable AD subjects and 11 as possible AD subjects. One hundred and twenty-seven subjects were considered to be cognitively normal and were used as controls. The frequencies of the E2 and E4 alleles in the Turkish population were among the lowest reported worldwide, and different from those of other Caucasian populations. Despite its overall low frequency, the E4 allele was almost twice as frequent in patients with AD, compared to controls. Multivariate analyses and odds ratios (OR) revealed that carrying at least one E4 allele constitutes a significant risk factor in sporadic AD in the Turkish population.