Familial aggregation of cervical artery dissection and cerebral aneurysm.

amyloidotic polyneuropathy, and Down's syndrome. Vascular dementia is a poorly defined disease and its diagnostic criteria are still a matter of debate. We examined e4 frequency in 19 patients with mixed and vascular dementia (mean age, 81.7 years; SD, 95) and in 76 patients with Alzheimer's disease (mean age, 78.4 years; SD, 7.7) by using a phenotyping technique. Our results are different from those of Frisoni et al (Table). Several factors might account for the discrepancy. First, the two groups in our study were small and interpretation of the results should be made cautiously. Second, the populations of the two studies had different mean ages. Third, the difference in findings could derive from the heterogeneity of cerebrovascular diseases that led to vascular dementia. Moreover, other environmental or genetic risk factors such as diet and hypertension should be taken into account. Far more patients need to be studied and additional clinical, biological, and genetic information will be necessary to determine whether the apo E e4 allele is indeed a specific risk factor for Alzheimer's disease.