Genetic and environmental risk factors for Alzheimer's disease in Israeli Arabs.

Abstract

We studied the genetic and environmental risk factors and prevalence, and incidence of dementia of the Alzheimer type (DAT) among the elderly in an Arab community in Israel. Epidemiological and genetic studies of dementia have rarely been reported in an Arab population. All persons aged 60 years or older who were residents of the rural area of Wadi Ara were examined for identification of DAT, vascular dementia (VaD) and conversion from age related cognitive decline (ARCD) to DAT using DSM-IV criteria and a semi-structured questionnaire for collection of demographic and medical data. ApoE genotype was also determined. Total plasma homocysteine (tHcy) was determined using HPLC with fluorescence detection. Vitamins B12 and plasma folate were determined using a commercial radioisotope dilution kit assay (ICN). DAT was diagnosed in 20.5% of this population. Its prevalence increased steeply with age. Illiteracy was very common, and strongly associated with higher prevalence of DAT. The annual incidence of DAT among ARCD cases was 4.4%. Subjects with ARCD who developed DAT were older than ARCD subjects who did not develop dementia. Hypertension was significantly more common among converted patients than among non-converted. Illiteracy was insignificantly more common among those who developed DAT than among those who remained ARCD. Vascular dementia (VaD) constitutes about 22% of the total dementia population. We also confirm the association between VaD, illiteracy and hypertension. Smoking did not represent a risk factor for VaD. The survival rates among the three groups (healthy subjects, ARCD and DAT) was 80.5%, 58.8% and 55.5% respectively. Homocysteine levels were significantly higher than found in studies in Cleveland. Plasma B12 and plasma folate levels did not differ significantly between DAT patients and controls after adjusting for year of birth. Our findings suggest that the Wadi Ara population is unique because of high prevalence rates of dementia. We found old age, female gender and lack of education to be risk factors for the development of DAT. The ApoE epsilon4 allele is relatively uncommon in this population and it cannot explain the high DAT prevalence. We also confirm the association between VaD, illiteracy and hypertension and older age and hypertension are risk factors for the transformation of ARCD to DAT.