Tolar et al. showed that not only is a 22 kDa N-terminalfragment of apoE4 neurotoxic, but that it is significantly more toxic than the samefragment derived from the E3 isoform [43].Unfortunately, much is still not known about the mechanism by which ApoE4contributes to the pathogenesis of AD. The gene discussed is APOE; the disease is Alzheimer disease.