Confirmation that familial clustering and age of onset in late onset Alzheimer's disease are determined at the apolipoprotein E locus.

We confirm that familial clustering in late onset Alzheimer's disease is associated with the zeta 4 allele of apolipoprotein E. This allele occurs in the great majority (82%) of late onset familial Alzheimer cases. Together with previously published data, it is suggested that the effect of a single zeta 4 allele is to increase the risk of developing AD by an amount equivalent to 5 years and that the effect of zeta 4 homozygosity is to increase the risk of developing AD by an amount equivalent to 10 years of age.