To the Editor.
—The association between apo E E4 and AD has been shown in patients with probable AD and in autopsyconfirmed AD cases. However, the specificity of apo E E4 as a risk factor for AD is not known. In a recent letter, Dr Frisoni and colleagues1 proposed that the frequency of apo E E4 is increased also in vascular dementia compared with that in controls.We analyzed apo E phenotypes in 30 patients with vascular dementia and 115 age-matched controls using isoelectric focusing and Western blotting as previously described.2 Vascular dementia was diagnosed according to the guidelines established by the NINDS-AIREN International Workshop.3 Seventeen patients with probable vascular dementia had a typical multi-infarct dementia. Possible vascular dementia was diagnosed in 13 patients, eight of whom were considered to have mixed dementia (ie, possible AD and concomitant significant cerebrovascular disease).No difference in apo E E4