Major genes recognised as responsible of familial forms of EOFAD are PSEN1, APP, and PSEN2. In particular, PSEN1 mutations have been found in 20% to 70% of all EOFAD, APP mutations in 10% to 15%, and PSEN2 mutations in about 5% [10,40]. This evidence concerns the gene PSEN2 and early-onset autosomal dominant Alzheimer disease.