Familial Alzheimer's disease. Evidences for clinical and genetic heterogeneity.

We report the genealogical, clinical and molecular genetic findings of a new family with autosomal dominant early-onset Alzheimer's disease (FAD) discovered in Torino (Italy). Up to now, the pedigree comprises 1500 members, distributed in 8 generations. 22 patients affected with Alzheimer's disease have been identified. The clinical course of the disease was fairly uniform in all the patients. An high incidence of myoclonic jerks and epileptic seizures was found. Molecular genetic studies showed the presence of positive but nonsignificant lod scores between chromosome 21 anonymous DNA markers and the disease. The data obtained from the Torino family were computed together with those of additional 47 pedigrees, with both early-onset and late-onset Alzheimer's disease. A predisposing locus for the disease was found on the pericentromeric region of chromosome 21 only in early-onset FAD pedigrees.