Increased prevalence of VNTR III of the insulin gene in women with gestational diabetes mellitus (GDM)

Abstract 

Objective

The VNTR polymorphism in the promoter region of the insulin gene (INS-VNTR) affects transcription rate and has been associated with insulin resistance and DM2. Gestational diabetes mellitus (GDM) is a multifactorial disorder, where both impaired insulin secretion and action may be involved. The aim of the study was to examine the distribution of the INS-VNTRs in women with GDM and to investigate possible associations with features of beta cell function and glycaemic control in this population.

Methods

One hundred and sixty-one women with GDM and 111 normal pregnant women (n) were genotyped for INS-VNTR during the 24th–32nd pregnancy week. Glucose and insulin levels were determined during the diagnostic OGTT. The majority of the previous GDM women were also examined at 3–6 months post-partum.

Results

VNTR class III/III genotype was significantly more frequent in the GDM group 8.7% versus 2.7%, p=0.02 giving an OR of 3.97 (1.1–14.29). An increased frequency of the VNTR class III allele was found in those GDM women who required insulin for treatment compared to those controlled with diet alone (12.4% versus 4%, p<0.001). Basal insulin levels tended to be lower in GDM women homozygous for the class III allele without reaching statistical significance (p=0.09).

Conclusions

The INS-VNTR class III is more frequent in women who develop GDM, and may be associated with decreased ability of the beta cell to meet the increased insulin requirements as reflected by the need for insulin supplementation for adequate glycaemic control.

Keywords: Gestational diabetes mellitus, Insulin, INS-VNTR, Beta cell, Gene polymorphism