PREVALENCE OF DEMENTIA OF ALZHEIMER-TYPE AND APOLIPOPROTEIN-E PHENOTYPES IN AGED PATIENTS WITH DOWNS-SYNDROME

We investigated the exact prevalence of dementia of Alzheimer type (DA T) and apolipoprotein E (ApoE) phenotypes in 106 Japanese Down's syndr ome (DS) patients. Among these patients 16 were diagnosed as having DA T. The prevalence of DAT was 0% in the 30- to 39-year-old group, 16% i n the 40- to 49-year-old group, and 38% in those over 50 years old. Th e frequency of the epsilon 4 allele in DS patients with DAT was 18.8%, which was considerably higher than that of nondemented DS patients (4 .5%) and Japanese nondemented controls (6.7%). Especially, the frequen cy of the epsilon 4 allele in DS patients who developed DAT under 50 y ears was significantly higher (28.6%). DS patients certainly develop D AT at earlier ages but the prevalence of DAT in each group of patients was lower than previously recognized, It is very likely that the ApoE epsilon 4 is a risk factor for DAT even in DS patients with a genetic predisposition to Alzheimer's disease.