rs7756992

This comprehensive review synthesizes literature on gestational diabetes mellitus (GDM), demonstrating its complex multifactorial etiology involving genetic factors (SNPs in GCKR, KCNQ1, MTNR1B, TCF7L2), epigenetic modifications (DNA methylation and microRNA expression), and alterations in microbial composition across multiple body sites. While certain SNP variants are associated with GDM phenotypes globally, genetic predisposition alone does not explain disease development; lifestyle factors can modify epigenetic signatures and microbiota composition to modulate risk. Evidence indicates genes, epigenetic alterations, and microbiota can transfer from mother to offspring with long-term health consequences.

This study examines the relationship between type 2 diabetes risk SNP rs7756992 in CDKAL1 and expression of the non-coding RNA CDKAL1-v1. While simple linear regression confirmed rs7756992's association with CDKAL1-v1 levels in UK whole blood (β=-0.75, p=0.005) and pancreatic islets (β=-1.07, p=0.009), multiple regression analysis revealed that rs9366357, a moderately linked SNP (r²=0.3), explains much more variance and renders the rs7756992 association non-significant or substantially reduced (β=-0.07, p=0.60 in Japanese cohort; β=-0.61, p=0.12 in islets). The authors conclude that dysregulated CDKAL1-v1 expression is unlikely to be the causal mechanism mediating the CDKAL1 locus association with diabetes risk.

Transethnic genome-wide meta-analysis in 159,940 individuals identified 60 common genetic variants associated with HbA1c levels. Variants were classified as glycemic (19), erythrocytic (22), or unclassified (19) based on their biological mechanisms. Glycemic variants were associated with higher type 2 diabetes risk (OR=1.05 per allele, p=3×10⁻²⁹), while erythrocytic variants were not. The X-linked G6PD G202A variant showed a large effect in African Americans (0.81% HbA1c reduction per allele) but minimal effects in other ancestries, potentially causing 2% of African American T2D cases to remain undiagnosed when using HbA1c screening.

Association analysis of 31 GWAS-confirmed type 2 diabetes SNPs in 3,089 Indian sib pairs (2,528 for quantitative traits, 561 for diabetes) identified significant associations with intermediate traits: CDKAL1 rs7756992, TCF7L2 rs7903146 and rs12255372 with fasting glucose (β=0.009-0.01, p≤0.01); ADAM30 rs2641348, NOTCH2 rs10923931, TCF-2/HNF1B rs757210, and CDKN2A/B rs10811661 with fasting insulin and HOMA-IR (β=±0.05-0.09, p≤0.05); and THADA rs7578597 with type 2 diabetes (OR 1.5, p=0.03).

This association study identified rs10811661 near CDKN2A/B on chromosome 9p21, a type 2 diabetes risk SNP, as significantly associated with diabetic nephropathy in 2,963 type 1 diabetes patients (OR 1.33, p=0.00045). The association was replicated in meta-analysis across four cohorts (n>5,000; OR 1.15, p=0.011) and was particularly strong for end-stage renal disease (OR 1.35, p=0.00038). The SNP was also associated with severe retinopathy but not cardiovascular disease.

This association study of 4,213 Danish individuals examined 25 type 2 diabetes risk variants and their association with birthweight. The study found that type 2 diabetes risk alleles near ADCY5 (rs11708067, β = -33 g, p = 0.004), CDKAL1 (rs7756992, β = -22 g, p = 0.04), and HHEX-IDE (rs1111875, β = -16 g in meta-analysis, p = 8×10⁻⁵, n = 25,164) were associated with reduced birthweight, supporting the fetal insulin hypothesis. Meta-analyses confirmed these associations and showed no strong general effect on birthweight from the 25 common type 2 diabetes risk alleles combined.

The HERITAGE Family Study examined eight type 2 diabetes susceptibility variants in 481 sedentary individuals undergoing 20-week endurance training. PPARG rs1801282 (Pro12Ala) was the only significant finding: Ala carriers showed greater improvements in glucose tolerance (p=0.0008), glucose effectiveness (p=0.004), and disposition index (p=0.003) in response to exercise training, though no associations were found with other recently identified GWAS variants.

This case-control study in 869 Korean women with gestational diabetes mellitus (GDM) and 632 non-diabetic controls examined whether type 2 diabetes-associated genetic variants discovered in recent GWAS are also associated with GDM. Multiple variants showed significant associations with GDM, including rs7756992 and rs7754840 in CDKAL1 (OR 1.55, p=4.17×10⁻⁹), rs10811661 in CDKN2A-CDKN2B (OR 1.49, p=1.05×10⁻⁷), variants in HHEX, rs4402960 in IGF2BP2 (OR 1.18, p=0.03), rs13266634 in SLC30A8 (OR 1.24, p=0.005), and rs7903146 in TCF7L2 (OR 1.58, p=0.038).

This case-control and family-based association study tested whether 18 type 2 diabetes susceptibility loci are associated with type 1 diabetes in 7,606 type 1 diabetic cases and 8,218 controls. Only PPARG (rs1801282/Pro12Ala, OR=0.91, p=0.004) and HHEX-IDE (rs1111875, OR=0.94, p=0.003) showed evidence of association with type 1 diabetes. The authors conclude that type 1 and type 2 diabetes do not share a common genetic background, supporting the view that type 1 diabetes is primarily an autoimmune disease.

This replication study tested newly identified type 2 diabetes susceptibility loci in a Norwegian population-based cohort of 1,638 type 2 diabetes patients and 1,858 controls. The authors confirmed associations for rs10811661 near CDKN2B (OR 1.20, p=0.004), rs9939609 in FTO (OR 1.14, p=0.006), and rs13266634 in SLC30A8 (OR 1.20, p=3.9×10⁻⁴). They found borderline association for rs4402960 in IGFBP2 (OR 1.10, p=0.074) but no support for SNPs near FLJ39370 and PKN2.

The D.E.S.I.R. prospective cohort study (N=4,707) validated 22 SNPs from genome-wide association studies for type 2 diabetes effects on glucose homeostasis. Risk alleles in SLC30A8 (rs13266634, P=0.0003), NGN3 (rs10823406, P=0.01), and MMP26 (rs2499953, P=0.04) were associated with elevated fasting glucose, while CDKAL1 variants (rs7756992, P=0.003) showed reduced fasting insulin. However, associations with type 2 diabetes incidence were modest (HRs ranging 1.25-2.03), and only SLC30A8 remained significant after Bonferroni correction for HOMA-B.

This case-control association study in 864 Japanese type 2 diabetes patients and 864 controls confirmed that three SNPs in HHEX (rs5015480 OR=1.46, rs7923837 OR=1.40, rs1111875 OR=1.30) were significantly associated with type 2 diabetes across ethnic groups. SNPs in FTO, CDKAL1, CDKN2B, and SLC30A8 showed nominal associations, while several SNPs were associated with impaired pancreatic beta cell function measured by HOMA-beta index.