PSEN2 and early-onset autosomal dominant Alzheimer disease: PRESENILIN 2 (PSEN2) was first identified as a candidate locus for mutations causing familial Alzheimer’s disease (AD) with early onset (EOfAD) when a point mutation resulting in the substitution of an isoleucine residue for an asparagine residue (N141I) was found in a Volga German AD family in 1995 [1].