CHOP T/C and C/T haplotypes contribute to early-onset type 2 diabetes in Italians.

Type 2 diabetes (T2D) is characterized by impaired insulin secretion, insulin insensitivity and decreased beta-cell mass. Multiple genes contribute to T2D. The chromosome 12q13.1 region is in linkage to T2D in different populations, including our Italian dataset. CHOP is a candidate gene for the linkage, as it is located in the chromosome 12q13.1 region, and may contribute to T2D by increasing beta-cell apoptosis susceptibility and by impairing insulin sensitivity. Our goal was to identify any potential CHOP gene variants contributing to T2D in our Italian early-onset T2D families, which show linkage to the CHOP region. We directly sequenced the CHOP gene in 28 Italian probands of the linked T2D families and in 115 control subjects. We performed genotype and haplotype association tests with T2D of the identified single nucleotide polymorphisms (SNPs). We performed model-free and parametric association haplotype tests with T2D. We identified three SNPs [5'UTR-c.279T > C, 5'UTR-c.120A > G and + nt30C > T (F10F)] in CHOP. These SNPs are in complete linkage disequilibrium. The genotype association test showed an association trend with T2D of TT (F10F) and AG (-c.120A > G). The haplotype association test provided significant results for the haplotypes T/C (frequency = 0.33) and C/T (frequency = 0.01) (at 5'UTR-c.279T > C and + nt30C > T, respectively) under non-parametric analysis (P-value = 0.0000), recessive model (P-value = 0.0000) and additive model (P-value = 0.0014). Our data show that CHOP described haplotypes T/C and C/T, as an additive and as a homozygous variant, contribute significantly to T2D in our Italian early-onset group. We conclude that the CHOP T/C and C/T haplotype contributes to our T2D linkage signal on chromosome 12q13.1.