Alzheimer's disease with spastic paraparesis and 'cotton wool' plaques: two pedigrees with PS-1 exon 9 deletions.

Several pedigrees have recently been reported in which dominantly inherited familial Alzheimer’s disease is associated in some family members with spastic paraparesis and non‐neuritic ‘cotton wool’ plaques. Here we report clinical, genetic and neuropathological findings in two further large pedigrees in which this combination of phenotypes is associated with a deletion of exon 9 of the presenilin‐1 (PS‐1) gene caused by mutations at the splice acceptor site. In both pedigrees, individuals with paraparesis at presentation had a later than average age at onset of symptoms. In addition, one subject with paraparesis had a much less prominent dementia syndrome than his dementia‐affected siblings. As PS‐1 mutations are almost always associated with a particularly aggressive form of presenile dementia, these findings suggest the existence of a protective or delaying factor in individuals with spastic paraparesis.