Biologic distinction between sporadic and familial Alzheimer disease by an in vitro cell fusion test

In vitro cell-fusing activity of brain suspensions prepared from patients with Alzheimer disease occurred in 10 of 17 familial cases (59%), a level similar to that seen in transmissible Creutzfeldt-Jakob disease (CJD), but in only 3 of 17 sporadic cases (17%), a level not statistically different from that in nonneurologic control patients. This biologic distinction between the familial and sporadic forms of Alzheimer disease may be related to the previously reported transmission to primates of a CJD-like disease from two familial cases of Alzheimer disease.