Mutations in the amyloid precursor protein gene were the first to be recognized as a cause of Alzheimers disease (AD).We describe 2 Italian families showing the missense mutation in exon 17 of the amyloid precursor protein gene on chromosome 21 (Val717Ile), known as London mutation.In 1 family, this mutation was responsible for AD in 3 out of 7 siblings and it is also present in a fourth sibling who has only shown signs of executive dysfunction so far