Evaluation of Polymorphic Splicing in the Mechanism of the Association of the Insulin Gene With Diabetes
- From the Endocrine Genetics Laboratory, McGill University Health Center Research Institute, Montréal, Québec, Canada
- Address correspondence and reprint requests to Constantin Polychronakos, MD, McGill University Health Center, Montreal Children’s Hospital, 2300 Tupper St., Ste. C244, Montreal, Quebec, Canada H3H 1P3. E-mail: constantin.polychronakos{at}mcgill.ca
Abstract
The association of type 1 diabetes with the insulin gene (IDDM2 locus) has been mapped to a short haplotype encompassing two single nucleotide polymorphisms (SNPs) in perfect linkage disequilibrium (r2 = 1) with each other and with the two allele classes at the variable number of tandem repeats (VNTR) polymorphism upstream of the transcription site. Although it is believed that the genetic effect is mediated through transcriptional effects of the VNTR, an alternative mechanism has been recently proposed: In transfected cells, the common A allele at one of the SNPs (−23A→T, in relation to the translation-initiation codon) weakens the splicing of intron 1, resulting in a minor (∼15% of total RNA) transcript with a longer 5′ untranslated region and sixfold enhanced translational efficiency. The purpose of our study was to confirm these findings in RNA from normal human pancreas and thymus. We report that pancreas does contain the alternative transcript in an allele-dependent manner but at a very low proportion (<5% of total INS mRNA). We believe that this level would have a minor, if any, biological effect involved in the mechanism of the IDDM2 locus.
- LD, linkage disequilibrium
- SNP, single nucleotide polymorphism
- UTR, untranslated region
- VNTR, variable number of tandem repeats
Footnotes
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Additional information for this article can be found in an online appendix at http://dx.doi.org/10.2337/db06-0402.
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- Accepted December 18, 2006.
- Received March 26, 2006.
- DIABETES
