Alpha2-macroglobulin polymorphisms in Alzheimer's disease and dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common cause of dementia in the elderly after Alzheimer's disease (AD). The apolipoprotein E gene (APOE) is a major risk factor, but can only account for approximately 50% of AD cases. Whole genome scanning in late-onset AD families has suggested that a locus on chromosome 12 may contribute significantly to disease development. Recently the alpha2-macroglobulin gene (A2M) on chromosome 12 has been suggested as a candidate locus for AD. We therefore determined the influence of two polymorphisms in A2M, a pentanucleotide deletion 5' to the bait domain exon, and a valine to isoleucine polymorphism in the thiolester site of the protein, in AD and DLB cohorts. No evidence was observed for an association between the thiolester or deletion polymorphisms and AD or DLB alone or when accounting for the APOE epsilon4 allele. We did, however, identify a non-significant excess of deletion homozygotes in the AD and DLB groups. This genotype accounted for 4% of disease cases but was absent in the control population. Given that the A2M deletion polymorphism is non-functional, the chromosome 12 AD/DLB locus may be situated elsewhere and not with these A2M polymorphisms.