Insulin gene VNTR polymorphisms −2221MspI and −23HphI are associated with type 1 diabetes and latent autoimmune diabetes in adults: a meta-analysis

Aims A variable number of tandem repeat (VNTRs) region in the insulin gene (INS) possibly influences the progression of type 1 diabetes (T1D) and latent autoimmune diabetes in adults (LADA). However, effects of INS VNTR polymorphisms in these contexts remain inconclusive. Methods We performed a systematic review of work on the INS VNTR −2221MspI and −23HphI polymorphisms to estimate the overall effects thereof on disease susceptibility; we included 17,498 T1D patients and 24,437 controls, and 1960 LADA patients and 5583 controls. Results For T1D, the C allele at −2221MspI and the A allele at −23HphI were associated with estimated relative risks of 2.13 (95 % CI 1.94, 2.35) and 0.46 (95 % CI 0.44, 0.48), which contributed to absolute increases of 46.76 and 46.98 % in the risk of all T1D, respectively. The estimated lambda values were 0.44 and 0.42, respectively, suggesting that a co-dominant model most likely explained the effects of −2221MspI and −23HphI on T1D. For −23HphI, the A allele carried an estimated relative risk of 0.55 (95 % CI 0.50, 0.61) for LADA and increased the risk of all LADA by 36.94 %. The λ value was 0.43, suggesting that a co-dominant model most likely explained the effect of −23HphI on LADA. Conclusions Our results support the existence of associations of INS with T1D and LADA.