Age of onset in familial early onset Alzheimer's disease correlates with genetic aetiology.

Age of onset is the most robust clinical feature demarcating aetiologic subtypes of familial Alzheimer's disease. It has previously been noted that early onset disease (arbitrarily below the age of 65 years) conforms to an autosomal dominant pattern of transmission. Late onset disease is generally thought to have a more complex aetiology. We present data here suggesting that early onset disease can be subdivided by genetic aetiology with which age of onset correlates. In general, those pedigrees showing linkage to the chromosome 14 locus have a mean age of onset in the forties whereas those pedigrees with an APP mutation have an age of onset in the fifties.