While late-onset alzheimers disease occurs in people aged 65 or older, familial alzheimers disease develops earlier because familial alzheimers disease is triggered by gene mutations of amyloid precursor protein  (chromosome 21), multiprotein complex comprising presenilin/PSEN 1 (chromosome 14), or PSEN 2 (chromosome 1), thereby eliciting beta-amyloid aggregation in earlier years. Of these three types, the PSEN 1 mutation has a relatively high proportion of beta-amyloid42. As beta-amyloid42 is more toxic than beta-amyloid40, familial alzheimers disease progresses more rapidly in this case, and the time of onset can come as early as 20-30 years of age.