To the Editor.
—In response to the letter by Dr Frisoni and colleagues1 that reported a series of 42 vascular dementia patients with an apolipoprotein E (apo E)E4 allele frequency equivalent to that reported for Alzheimer's disease (AD), we believe that their cases represent AD patients who share a clinically suggested diagnosis of vascular dementia.Frisoni et al do not provide convincing evidence that their patients diagnosed as having vascular dementia do not also have AD. The cited "research criteria" (NINDS-AIREN2) provide for a diagnosis of probable or possible vascular dementia during life. These research criteria have yet to be tested with postmortem validation. It should also be noted that Roman and Tatemichi, coauthors of the published NINDS-AIREN criteria, more recently commented that the "criteria do not dismiss the coexistence of AD and vascular dementia."3 Roman and Tatemichi also commented that "in the absence of laboratory tests