Genetic factors contribute to the development of NIDDM, and genes involved in regulating pancreatic β-cell function and insulin's effects on glucose metabolism are good candidates for being NIDDM susceptibility loci. However, testing candidate genes for linkage to NIDDM depends on the identification of highly informative DNA polymorphisms in or near the candidate locus. Here we describe an approach for identifying highly polymorphic markers near candidate genes that utilizes the emerging physical map of the human genome. A sequence-tagged site from the candidate gene is used to screen the Centre d'Etude du Polymorphisme Humain megabase-insert yeast artificial chromosome library, which contains information on the physical localization of >3,000 genetically mapped simple sequence repeat DNA polymorphisms. Thus, identification of a yeast artificial chromosome containing the candidate locus will in many instances also identify a physically linked simple sequence repeat DNA polymorphism that can be used as a marker for the candidate gene in linkage studies. We have used this approach to identify a marker for the islet amyloid polypeptide gene on chromosome 12. The physical mapping of this gene to a yeast artificial chromosome showed that it was in the same yeast artificial chromosome as the gene encoding liver glycogen synthase, another possible NIDDM susceptibility gene. Affected sib pair studies using a simple sequence repeat DNA polymorphism physically linked to the islet amyloid polypeptide and liver glycogen synthase genes showed no evidence for linkage with NIDDM, indicating that they are not major genes contributing to NIDDM susceptibility.

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