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Evaluation of four novel genetic variants affecting hemoglobin A1c levels in a population-based type 2 diabetes cohort (the HUNT2 study).

Hertel JK, Johansson S, Ræder H, Platou CG, Midthjell K, Hveem K, Molven A, Njølstad PR - BMC Med. Genet. (2011)

Bottom Line: Through regression models, we examined their effects on HbA1c and non-fasting glucose levels individually and in a combined genetic score model.No significant associations with HbA1c or glucose levels were found for the SORCS1, BNC2, GSC or WDR72 variants (all P-values > 0.05).In contrast, the WDR72 risk variant showed a borderline association with reduced HbA1c levels (β = -0.21, P = 0.06), and direction consistent with decreased glucose levels (β = -0.29, P = 0.29).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway.

ABSTRACT

Background: Chronic hyperglycemia confers increased risk for long-term diabetes-associated complications and repeated hemoglobin A1c (HbA1c) measures are a widely used marker for glycemic control in diabetes treatment and follow-up. A recent genome-wide association study revealed four genetic loci, which were associated with HbA1c levels in adults with type 1 diabetes. We aimed to evaluate the effect of these loci on glycemic control in type 2 diabetes.

Methods: We genotyped 1,486 subjects with type 2 diabetes from a Norwegian population-based cohort (HUNT2) for single-nucleotide polymorphisms (SNPs) located near the BNC2, SORCS1, GSC and WDR72 loci. Through regression models, we examined their effects on HbA1c and non-fasting glucose levels individually and in a combined genetic score model.

Results: No significant associations with HbA1c or glucose levels were found for the SORCS1, BNC2, GSC or WDR72 variants (all P-values > 0.05). Although the observed effects were non-significant and of much smaller magnitude than previously reported in type 1 diabetes, the SORCS1 risk variant showed a direction consistent with increased HbA1c and glucose levels, with an observed effect of 0.11% (P = 0.13) and 0.13 mmol/l (P = 0.43) increase per risk allele for HbA1c and glucose, respectively. In contrast, the WDR72 risk variant showed a borderline association with reduced HbA1c levels (β = -0.21, P = 0.06), and direction consistent with decreased glucose levels (β = -0.29, P = 0.29). The allele count model gave no evidence for a relationship between increasing number of risk alleles and increasing HbA1c levels (β = 0.04, P = 0.38).

Conclusions: The four recently reported SNPs affecting glycemic control in type 1 diabetes had no apparent effect on HbA1c in type 2 diabetes individually or by using a combined genetic score model. However, for the SORCS1 SNP, our findings do not rule out a possible relationship with HbA1c levels. Hence, further studies in other populations are needed to elucidate whether these novel sequence variants, especially rs1358030 near the SORCS1 locus, affect glycemic control in type 2 diabetes.

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Related in: MedlinePlus

Mean HbA1c (black circles) and frequency (bars) of type 2 diabetes individuals plotted against the number of risk alleles carried, and the relationship between BNC2 (rs10810632), SORCS1 (rs1358030), GSC (rs11624318) and WDR72 (rs566369) combined genotypes and mean HbA1c. Only individuals genotyped for all variants are included (n = 1,403). The black line is the fitted HbA1c linear regression line with the area between the dashed curves representing the 95% confidence interval.
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Figure 1: Mean HbA1c (black circles) and frequency (bars) of type 2 diabetes individuals plotted against the number of risk alleles carried, and the relationship between BNC2 (rs10810632), SORCS1 (rs1358030), GSC (rs11624318) and WDR72 (rs566369) combined genotypes and mean HbA1c. Only individuals genotyped for all variants are included (n = 1,403). The black line is the fitted HbA1c linear regression line with the area between the dashed curves representing the 95% confidence interval.

Mentions: Even though the four examined loci were not significantly associated with increased HbA1c values at an individual level, three of the four risk variants showed concordance in allelic direction in which individuals carrying the risk allele had higher HbA1c. When we included all four variants in a combined genetic score model we observed, however, no evidence for a relationship between increasing number of risk alleles and increasing HbA1c levels (P = 0.38). Each additional risk allele demonstrated an increase in HbA1c of approximately 0.04% (Table 3, Figure 1).


Evaluation of four novel genetic variants affecting hemoglobin A1c levels in a population-based type 2 diabetes cohort (the HUNT2 study).

Hertel JK, Johansson S, Ræder H, Platou CG, Midthjell K, Hveem K, Molven A, Njølstad PR - BMC Med. Genet. (2011)

Mean HbA1c (black circles) and frequency (bars) of type 2 diabetes individuals plotted against the number of risk alleles carried, and the relationship between BNC2 (rs10810632), SORCS1 (rs1358030), GSC (rs11624318) and WDR72 (rs566369) combined genotypes and mean HbA1c. Only individuals genotyped for all variants are included (n = 1,403). The black line is the fitted HbA1c linear regression line with the area between the dashed curves representing the 95% confidence interval.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3044669&req=5

Figure 1: Mean HbA1c (black circles) and frequency (bars) of type 2 diabetes individuals plotted against the number of risk alleles carried, and the relationship between BNC2 (rs10810632), SORCS1 (rs1358030), GSC (rs11624318) and WDR72 (rs566369) combined genotypes and mean HbA1c. Only individuals genotyped for all variants are included (n = 1,403). The black line is the fitted HbA1c linear regression line with the area between the dashed curves representing the 95% confidence interval.
Mentions: Even though the four examined loci were not significantly associated with increased HbA1c values at an individual level, three of the four risk variants showed concordance in allelic direction in which individuals carrying the risk allele had higher HbA1c. When we included all four variants in a combined genetic score model we observed, however, no evidence for a relationship between increasing number of risk alleles and increasing HbA1c levels (P = 0.38). Each additional risk allele demonstrated an increase in HbA1c of approximately 0.04% (Table 3, Figure 1).

Bottom Line: Through regression models, we examined their effects on HbA1c and non-fasting glucose levels individually and in a combined genetic score model.No significant associations with HbA1c or glucose levels were found for the SORCS1, BNC2, GSC or WDR72 variants (all P-values > 0.05).In contrast, the WDR72 risk variant showed a borderline association with reduced HbA1c levels (β = -0.21, P = 0.06), and direction consistent with decreased glucose levels (β = -0.29, P = 0.29).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway.

ABSTRACT

Background: Chronic hyperglycemia confers increased risk for long-term diabetes-associated complications and repeated hemoglobin A1c (HbA1c) measures are a widely used marker for glycemic control in diabetes treatment and follow-up. A recent genome-wide association study revealed four genetic loci, which were associated with HbA1c levels in adults with type 1 diabetes. We aimed to evaluate the effect of these loci on glycemic control in type 2 diabetes.

Methods: We genotyped 1,486 subjects with type 2 diabetes from a Norwegian population-based cohort (HUNT2) for single-nucleotide polymorphisms (SNPs) located near the BNC2, SORCS1, GSC and WDR72 loci. Through regression models, we examined their effects on HbA1c and non-fasting glucose levels individually and in a combined genetic score model.

Results: No significant associations with HbA1c or glucose levels were found for the SORCS1, BNC2, GSC or WDR72 variants (all P-values > 0.05). Although the observed effects were non-significant and of much smaller magnitude than previously reported in type 1 diabetes, the SORCS1 risk variant showed a direction consistent with increased HbA1c and glucose levels, with an observed effect of 0.11% (P = 0.13) and 0.13 mmol/l (P = 0.43) increase per risk allele for HbA1c and glucose, respectively. In contrast, the WDR72 risk variant showed a borderline association with reduced HbA1c levels (β = -0.21, P = 0.06), and direction consistent with decreased glucose levels (β = -0.29, P = 0.29). The allele count model gave no evidence for a relationship between increasing number of risk alleles and increasing HbA1c levels (β = 0.04, P = 0.38).

Conclusions: The four recently reported SNPs affecting glycemic control in type 1 diabetes had no apparent effect on HbA1c in type 2 diabetes individually or by using a combined genetic score model. However, for the SORCS1 SNP, our findings do not rule out a possible relationship with HbA1c levels. Hence, further studies in other populations are needed to elucidate whether these novel sequence variants, especially rs1358030 near the SORCS1 locus, affect glycemic control in type 2 diabetes.

Show MeSH
Related in: MedlinePlus