Association of the HLA-A2 allele with an earlier age of onset of Alzheimer's disease.

Abstract

The HLA-A2 allele has recently been considered as a risk factor in AD by advancing the age at onset of the disease, especially in subjects who were homozygous for the apoE epsilon4 allele. We examined the distribution of apoE genotypes and A2 allele as a function of age at onset in 109 patients with sporadic and familial AD. In the early onset (< or =60 years) and late onset (>75 years) AD groups, there was, respectively, a 2.2 year and a 2.7 year earlier onset in the A2 positive cases. Age effect was not apparent in the middle onset (61-75 years) AD group. The effect of A2 allele on the age at onset was not different between familial and sporadic AD cases. The presence or absence of the A2 allele did not modify mean age at onset in the groups homozygous and heterozygous for epsilon4, and in cases with no epsilon4 alleles. Though the sample size was small, there is a trend in favor of an A2 effect on age at onset. Additionally, there is no evidence of interaction between A2 and apoE epsilon4 alleles on age at onset of AD.