Identification of chromosome 21 DNA polymorphisms for genetic studies in Alzheimer's disease and Down syndrome.

Linkage studies in families with presenile onset of Alzheimer's disease (AD) indicated the presence of a predisposing gene on the proximal long arm of chromosome 21. We mapped four new loci in the candidate AD region using somatic cell hybrids. For three of the four loci, several restriction fragment length polymorphisms were found; for one locus, a multiallelic (CA)n dinucleotide polymorphism was detected. Preliminary genetic mapping of the new polymorphic loci relative to the AD-linked loci was obtained in a reference pedigree. In addition, we used the (CA)n dinucleotide polymorphism to reconstruct the non-disjunction event in a Down syndrome (DS) patient whose mother died of familial AD.