Association of apolipoprotein E polymorphism in late-onset Alzheimer's disease and vascular dementia in Brazilians

Abstract

The genetic basis for dementias is complex. A common polymorphism in the apolipoprotein E (APOE) gene is considered to be the major risk factor in families with sporadic and late-onset Alzheimer's disease as well as in the general population. The distribution of alleles and genotypes of the APOE gene in late-onset Alzheimer's disease (N = 68), other late-life dementias (N = 39), and in cognitively normal controls (N = 58) was determined, as also was the risk for Alzheimer's disease associated with the E4 allele. Peripheral blood samples were obtained from a total of 165 individuals living in Brazil aged 65-82 years. Genomic DNA was amplified by the polymerase chain reaction and the products were digested with HhaI restriction enzyme. APOE E2 frequency was considerably lower in the Alzheimer's disease group (1%), and the E3 allele and E3/E3 genotype frequencies were higher in the controls (84 and 72%, respectively) as were the E4 allele and E3/E4 genotype frequencies in Alzheimer's disease (25 and 41%, respectively). The higher frequency of the E4 allele in Alzheimer's disease confirmed its role as a risk factor, while E2 provided a weak protection against development of the disease. However, in view of the unexpectedly low frequency of the E4 allele, additional analyses in a more varied Brazilian sample are needed to clarify the real contribution of apolipoprotein E to the development of Alzheimer's disease in this population.