Association of tyrosine hydroxylase 01 (TH01) microsatellite and insulin gene (INS) variable number of tandem repeat (VNTR) with type 2 diabetes and fasting insulin secretion in Mexican population

Purpose A variable number of tandem repeats (VNTR) in the insulin gene (INS) control region may be involved in type 2 diabetes (T2D). The TH01 microsatellite is near INS and may regulate it. We investigated whether the TH01 microsatellite and INS VNTR, assessed via the surrogate marker single nucleotide polymorphism rs689, are associated with T2D and serum insulin levels in a Mexican population. Methods We analyzed a main case-control study (n = 1986) that used univariate and multivariate logistic regression models to calculate the risk conferred by TH01 and rs689 loci for T2D development; rs689 results were replicated in other casecontrol (n = 1188) and cross-sectional (n = 1914) studies. Results TH01 alleles 6, 8, 9, and 9.3 and allele A of rs689 were independently associated with T2D, with differences between sex and age at diagnosis. TH01 alleles with >= 8 repeats conferred an increased risk for T2D in males compared with <= 7 repeats (odds ratio, >= 1.46; 95% confidence interval, 1.1-1.95). In females, larger alleles conferred a 1.5-fold higher risk for T2D when diagnosed >= 46 years but conferred protection when diagnosed <= 45 years. Similarly, rs689 allele A was associated with T2D in these groups. In males, larger TH01 alleles and the rs689 A allele were associated with a significant decrease in median fasting plasma insulin concentration with age in T2D cases; the reverse occurred in controls. Conclusion Larger TH01 alleles and rs689 A allele may potentiate insulin synthesis in males without T2D, a process disabled in those with T2D.