Non-insulin-dependent (type 2) diabetes mellitus (NIDDM) is a common disorder of middle-aged individuals characterized by high blood glucose levels which, if untreated, can cause serious medical complications and lead to early death. Genetic factors play an important role in determining susceptibility to this disorder. However, the number of genes involved, their chromosomal location and the magnitude of their effect on NIDDM susceptibility are unknown. We have screened the human genome for susceptibility genes for NIDDM using non-and quasi-parametric linkage analysis methods in a group of Mexican American affected sib pairs. One marker, D2S125, showed significant evidence of linkage to NIDDM and appears to be a major factor affecting the development of diabetes mellitus in Mexican Americans. We propose that this locus be designated NIDDM1.

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The expansion of trinucleotide repeats has been associated with late-onset neurodegenerative disorders. Although the genes harbouring the triplet expansions may be widely expressed, the pathological expression of these diseases is restricted to specific tissues. Non-insulin-dependent diabetes mellitus (NIDDM) shares several features with diseases resulting from such dynamic mutations including late-onset and specific but limited sites of tissue pathology-muscle, fat, liver and insulin-secreting pancreatic beta cells. In order to examine the contribution of genes containing polymorphic CAG/CTG repeats to the development of NIDDM, we screened an adult human skeletal muscle cDNA library for expressed sequences containing tandem repeats of CAG and/ or CTG. Ten different loci with polymorphic CAG/ CTG repeats were identified, of which seven had a heterozygosity greater than 0.20. There was no evidence for linkage between these seven loci and NIDDM in a group of affected Mexican-American sib pairs. Nor was there a significant difference in the distribution of alleles between Caucasian patients with NIDDM and normal healthy control subjects or evidence for repeat expansion in diabetic subjects. Thus, muscle genes with polymorphic CAG/CTG repeats do not appear to play a significant role in the development of NIDDM.

The expansion of trinucleotide repeats has been associated with late-onset neurodegenerative disorders. Although the genes harbouring the triplet expansions may be widely expressed, the pathological expression of these diseases is restricted to specific tissues. Non-insulin-dependent diabetes mellitus (NIDDM) shares several features with diseases resulting from such dynamic mutations including late-onset and specific but limited sites of tissue pathology-muscle, fat, liver and insulin-secreting pancreatic beta cells. In order to examine the contribution of genes containing polymorphic CAG/CTG repeats to the development of NIDDM, we screened an adult human skeletal muscle cDNA library for expressed sequences containing tandem repeats of CAG and/ or CTG. Ten different loci with polymorphic CAG/ CTG repeats were identified, of which seven had a heterozygosity greater than 0.20. There was no evidence for linkage between these seven loci and NIDDM in a group of affected Mexican-American sib pairs. Nor was there a significant difference in the distribution of alleles between Caucasian patients with NIDDM and normal healthy control subjects or evidence for repeat expansion in diabetic subjects. Thus, muscle genes with polymorphic CAG/CTG repeats do not appear to play a significant role in the development of NIDDM.