The association between diabetes mellitus and polymorphism in the human insulin gene will be evaluated. In preliminary studies, DNA from 165 unrelated individuals has been analyzed by Southern blot analysis with a cloned genomic human insulin probe. DNA insertions of 1.6 to 3.4 kilobase pairs (kb) were found about 0.7 kb upstream from the insulin gene, and their presence was positively correlated with non-insulin dependent diabetes. The magnitude of this correlation appears to vary with race. A reasonable hypothesis to explain the above results is the insertions 5 feet to the human insulin gene limit the maximal biosynthetic capacity of the gene, resulting in a dominant genotype with variable penetrance (the latter perhaps controlled by genetic background and dietary stress). To test this hypothesis four types of experiments are proposed. 1. Population studies will be carried out by Southern blot analysis of six groups: Black, Pima Indian, and Caucasian non-insulin dependent diabetics and non-diabetics. To place the correlation between DNA inserts and diabetes at an adequate statistical confidence level, preliminary studies will be extended to about 50 individuals in each group. Clinical characteristics of diabetics with and without insertions will be analyzed to determine whether insertions define genetic subsets of non-insulin dependent diabetes. 2. Family studies will be carried out to determine if polymorphic insulin alleles are always inherited in a stable Medelian fashion and to evaluate the association between insertions and diabetes where conditions responsible for variable penetrance are minimized. 3. DNA sequence studies will reveal the nature of the inserted DNA regions from insulin genes isolated from recombinant DNA libraries constructed from genomic DNA obtained from patients with variant alleles. Insert specific probes will be made by subcloning and used to hybridize to genomic DNA to examine whether insert DNA varies among individuals. 4. Further insulin gene polymorphisms will be sought through an extensive Southern blot analysis using a wide variety of restriction endonucleases. Restriction site markers may be found which show different associations with diabetes than that already found for the 5 feet length polymorphisms.
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