Recently, some Alzheimer-associated genes have been found: amyloid beta protein precursor (APP), apolipoprotein E (apoE), presenilin 1 (PS-1), and presenilin 2 (PS-2). First, we failed to discover other susceptibility genes of familial Alzheimer's disease (FAD). However, we disClosed a novel mutation. Asp678Asn (D678N), in the APP gene in a pedigree of early-onset Japanese FAD. The alteration in the aggregation properties of mutant A beta may be involved in the pathogenesis of FAD with D678N APP mutation. Many reports have established that apoE genotype distribution for the epsilon 4 allele is a susceptibility factor for the earlier onset and more rapid progression of Alzheimer's disease (AD). However, the cause of sporadic AD (SAD) has not been elucidated fully. Other genetic factors may be associated with development of SAD. Second, we investigated the association between polymorphisms of the estrogen receptor (ER) alpha gene and SAD. The frequencies of P and X alleles in SAD were significantly higher than those in the control group (p < 0.05). Polymorphism of the ER alpha gene may be a genetic risk factor for SAD.