Apolipoprotein E type ε4 allele, heritability and age at onset in twins with Alzheimer disease and vascular dementia

Abstract

The apolipoprotein E (APOE) ε4 allele is a risk factor in Alzheimer disease (AD), but not in vascular dementia (VaD). We have investigated whether the ε4 allele is more common in twin pairs concordant for AD, compared with those discordant for AD, and whether the ε4 allele is more common in AD twins than in VaD twins. In addition, we have investigated the relationship of the ε4 allele and the age at onset in AD and VaD. APOE genotype was analysed in 29 senile demented twin pairs. The ε4 allele was associated with AD and not with VaD. However, there was no difference in the frequency of the APOE ε4 allele in concordant (33.3%) and discordant (31.3%) AD dizygotic twin pairs. Age at onset in AD was significantly lower in ε4 homozygotes than in individuals with one or no copies of ε4 (62.4 vs. 73.5, p < 0.01). In concordant AD twin pairs, the ε4 allele frequency was somewhat higher in the twins with earlier onset (41.7% vs. 25%), but the difference was not statistically significant. In the VaD group the age at onset was not significantly different between individuals with or without ε4 in their genotypes.