We have sequenced the insulin gene in 72 unrelated Japanese subjects (52 with type 2 diabetes mellitus and 20 with normal glucose tolerance). We identified 6 mutations and all were found at a low frequency (1% to 4%). Three mutations were new. These included a C-to-G substitution in the promoter region, a G-to-A substitution in codon-2 resulting in an Ala-to-Thr replacement in amino acid -2 of the signal peptide, and a G-to-A substitution in intron 2. We have no evidence that any of the mutations that we found are the cause of diabetes. Thus, mutations in the insulin gene do not appear to be an important genetic factor contributing to the development of diabetes in this population.
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