Objective: To study the contribution of single nucleotide polymorphism-UCSNP44 at calpain-10 gene (CAPN-10) on NIDDM1 locus to type 2 diabetes mellitus (T2DM) in Chinese.
Methods: 276 Chinese living in Shanghai, 148 with normal glucose tolerance (NGT) and 128 with T2DM were given 75 g glucose. O, 30, 60, 120, and 180 minutes later their plasma glucose (PG), insulin (INS), C-peptide (CP), and free fatty acids (FFA) were measured and the areas under curve (AUC) were calculated. The islet beta-cell insulin secretion and tissue insulin sensitivity were estimated by formulae of homeostasis model assessment and increment ratio of insulin to glucose levels 30 minutes after glucose challenge. The CAPN-10 UCSNP44 as well as UCSNP43 were genotyped by automated DNA direct sequencing.
Results: (1) The major genotype of CAPN-10 UCSNP44 in persons with NGT was TT (with a frequency of 0.82); the major allele was T (0.91). The most frequent genotype combination between UCSNP44 and UCSNP43 was TT-GG (corresponding to haplotype combination TG/TG) (0.64). The most frequent haplotype was TG (0.80). The D value for linkage disequilibrium between UCSNP44 and UCSNP43 was -0.11. (2) The frequencies of UCSNP44 and UCSNP44/UCSNP43 haplotype combination did not differ significantly between subjects with NGT and those with T2DM. (3) The PG levels in T2DM subjects with UCSNP44 TT genotype both at fasting and after glucose challenge were statistically significantly higher than those in subjects with non-TT (TC + CC) genotype, especially the PG levels 0, 60, 120, and 180 minutes after glucose challenge (P = 0.036, 0.040, 0.020, and 0.017) and the PG-AUC (P = 0.013). The PG levels and PG-AUC 0 and 120 minutes after glucose challenge were still significant after adjusted with age, sex, and body mass index and waist circumference. Similar results were observed in comparison between the TG/TG and TG/CG subgroups of UCSNP44/UCSNP43 haplotype combination. In addition, T2DM subjects with UCSNP44 TT genotype had lower CP levels after glucose challenge than those with non-TT genotype. However, the difference became not statistically significant after adjusted with above-mentioned variables.
Conclusion: The variation of CAPN-10 UCSNP44 has an impact on plasma glucose levels at fasting and after glucose challenge in subjects with type 2 diabetes. The relevant mechanism remains to be elucidated.