Since the report of a double mutation at codons 670 and 671 of the amyloid precursor protein (APP) gene identified in two Swedish families with clinically diagnosed Alzheimer's disease (AD), a carrier with dementia has died. Neuropathology confirmed the clinical diagnosis of AD. Genealogical investigations have confirmed that the two families are related to common founders. Two-point linkage analysis of the mutation versus the disease in the revised pedigree now gives a lod score of 7.62.