Henna Cederberg

Exome array analysis identifies new loci and low-frequency variants influencing insulin processing and secretion

Insulin secretion has a crucial role in glucose homeostasis, and failure to secrete sufficient insulin is a hallmark of type 2 diabetes. Genome-wide association studies (GWAS) have identified loci contributing to insulin processing and secretion; however, a substantial fraction of the genetic contribution remains undefined. To examine low-frequency (minor allele frequency (MAF) 0.5–5%) and rare (MAF < 0.5%) nonsynonymous variants, we analyzed exome array data in 8,229 nondiabetic Finnish males using the Illumina HumanExome Beadchip. We identified low-frequency coding variants associated with fasting proinsulin concentrations at the SGSM2 and MADD GWAS loci and three new genes with low-frequency variants associated with fasting proinsulin or insulinogenic index: TBC1D30, KANK1 and PAM. We also show that the interpretation of single-variant and gene-based tests needs to consider the effects of noncoding SNPs both nearby and megabases away. This study demonstrates that exome array genotyping is a valuable approach to identify low-frequency variants that contribute to complex traits.

Hyperglycemia and a Common Variant of GCKR Are Associated With the Levels of Eight Amino Acids in 9,369 Finnish Men

We investigated the association of glycemia and 43 genetic risk variants for hyperglycemia/type 2 diabetes with amino acid levels in the population-based Metabolic Syndrome in Men (METSIM) Study, including 9,369 nondiabetic or newly diagnosed type 2 diabetic Finnish men. Plasma levels of eight amino acids were measured with proton nuclear magnetic resonance spectroscopy. Increasing fasting and 2-h plasma glucose levels were associated with increasing levels of several amino acids and decreasing levels of histidine and glutamine. Alanine, leucine, isoleucine, tyrosine, and glutamine predicted incident type 2 diabetes in a 4.7-year follow-up of the METSIM Study, and their effects were largely mediated by insulin resistance (except for glutamine). We also found significant correlations between insulin sensitivity (Matsuda insulin sensitivity index) and mRNA expression of genes regulating amino acid degradation in 200 subcutaneous adipose tissue samples. Only 1 of 43 risk single nucleotide polymorphisms for type 2 diabetes or hyperglycemia, the glucose-increasing major C allele of rs780094 of GCKR, was significantly associated with decreased levels of alanine and isoleucine and elevated levels of glutamine. In conclusion, the levels of branched-chain, aromatic amino acids and alanine increased and the levels of glutamine and histidine decreased with increasing glycemia, reflecting, at least in part, insulin resistance. Only one single nucleotide polymorphism regulating hyperglycemia was significantly associated with amino acid levels.

Postchallenge Glucose, A1C, and Fasting Glucose as Predictors of Type 2 Diabetes and Cardiovascular Disease A 10-year prospective cohort study

OBJECTIVE A1C has been proposed as a new indicator for high risk of type 2 diabetes. The long-term predictive power and comparability of elevated A1C with the currently used high-risk indicators remain unclear. We assessed A1C, impaired glucose tolerance (IGT), and impaired fasting glucose (IFG) as predictors of type 2 diabetes and cardiovascular disease (CVD) at 10 years. RESEARCH DESIGN AND METHODS This prospective population-based study of 593 inhabitants from northern Finland, born in 1935, was conducted between 1996 and 2008. An oral glucose tolerance test (OGTT) was conducted at baseline and follow-up, and A1C was determined at baseline. Those with a history of diabetes were excluded from the study. Elevated A1C was defined as 5.7–6.4%. Incident type 2 diabetes was confirmed by two OGTTs. Cardiovascular outcome was measured as incident CVD or CVD mortality. Multivariate log-binomial regression models were used to predict diabetes, CVD, and CVD mortality at 10 years. Receiver operating characteristic curves compared predictive values of A1C, IGT, and IFG. RESULTS Incidence of diabetes during the follow-up was 17.1%. Two of three of the cases of newly diagnosed diabetes were predicted by a raise in ≥1 of the markers. Elevated A1C, IGT, or IFG preceded diabetes in 32.8, 40.6, and 21.9%, respectively. CVD was predicted by an intermediate and diabetic range of 2-h glucose but only by diabetic A1C levels in women. CONCLUSIONS A1C predicted 10-year risk of type 2 diabetes at a range of A1C 5.7–6.4% but CVD only in women at A1C ≥6.5%.

Glycerol and Fatty Acids in Serum Predict the Development of Hyperglycemia and Type 2 Diabetes in Finnish Men

OBJECTIVE We investigated the association of fasting serum glycerol and fatty acids (FAs) as predictors for worsening of hyperglycemia and incident type 2 diabetes. RESEARCH DESIGN AND METHODS Cross-sectional and longitudinal analyses of the population-based METabolic Syndrome in Men (METSIM) Study included 9,398 Finnish men (mean age 57 ± 7 years). At baseline, levels of serum glycerol, free FAs (FFAs), and serum FA profile, relative to total FAs, were measured with proton nuclear magnetic resonance spectroscopy. RESULTS At baseline, levels of glycerol, FFAs, monounsaturated FAs, saturated FAs, and monounsaturated n-7 and -9 FAs, relative to total FAs, were increased in categories of fasting and 2-h hyperglycemia, whereas the levels of n-3 and n-6 FAs, relative to total FAs, decreased (N = 9,398). Among 4,335 men with 4.5-year follow-up data available, 276 developed type 2 diabetes. Elevated levels of glycerol, FFAs, monounsaturated FAs, and saturated and monounsaturated n-7 and -9 FAs, relative to total FAs, predicted worsening of hyperglycemia and development of incident type 2 diabetes after adjustment for confounding factors. n-6 FAs, mainly linoleic acid (LA), relative to total FAs, were associated with reduced risk for the worsening of hyperglycemia and conversion to type 2 diabetes. CONCLUSIONS Our large population-based study shows that fasting serum levels of glycerol, FFAs, monounsaturated FAs, saturated FAs, and n-7 and -9 FAs are biomarkers for an increased risk of development of hyperglycemia and type 2 diabetes, whereas high levels of serum n-6 FAs, reflecting dietary intake of LA, were associated with reduced risk for hyperglycemia and type 2 diabetes.

Association of erythrocyte membrane fatty acids with changes in glycemia and risk of type 2 diabetes

BACKGROUND The significance of erythrocyte membrane fatty acids (EMFAs) and their ratios to predict hyperglycemia and incident type 2 diabetes is unclear. OBJECTIVE We investigated EMFAs as predictors of the worsening of hyperglycemia and incident type 2 diabetes in a 5-y follow-up of a population-based study. DESIGN We measured EMFAs in 1346 Finnish men aged 45-73 y at baseline [mean ± SD age: 55 ± 6 y; body mass index (in kg/m(2)): 26.5 ± 3.5]. Our prospective follow-up study included only men who were nondiabetic at baseline and who had data available at the 5-y follow-up visit (n = 735). RESULTS Our study showed that, after adjustment for confounding factors, palmitoleic acid (16:1n-7; P = 2.8 × 10(-7)), dihomo-γ-linolenic acid (20:3n-6; P = 2.3 × 10(-4)), the ratio of 16:1n-7 to 16:0 (P = 1.6 × 10(-8)) as a marker of stearoyl coenzyme A desaturase 1 activity, and the ratio of 20:3n-6 to 18:2n-6 (P = 9.4 × 10(-7)) as a marker of Δ(6)-desaturase activity significantly predicted the worsening of hyperglycemia (glucose area under the curve in an oral-glucose-tolerance test). In contrast, linoleic acid (18:2n-6; P = 0.0015) and the ratio of 18:1n-7 to 16:1n-7 (P = 1.5 × 10(-9)) as a marker of elongase activity had opposite associations. Statistical significance persisted even after adjustment for baseline insulin sensitivity, insulin secretion, and glycemia. Palmitoleic acid (P = 0.010) and the ratio of 16:1n-7 to 16:0 (P = 0.004) nominally predicted incident type 2 diabetes, whereas linoleic acid had an opposite association (P = 0.004), and n-3 polyunsaturated fatty acids did not show any associations. CONCLUSION EMFAs and their ratios are associated longitudinally with changes in glycemia and the risk type 2 diabetes.

Genetic regulation of human adipose microRNA expression and its consequences for metabolic traits

The genetics of messenger RNA (mRNA) expression has been extensively studied in humans and other organisms, but little is known about genetic factors contributing to microRNA (miRNA) expression. We examined natural variation of miRNA expression in adipose tissue in a population of 200 men who have been carefully characterized for metabolic syndrome (MetSyn) phenotypes as part of the Metabolic Syndrome in Men (METSIM) study. We genotyped the subjects using high-density single-nucleotide polymorphism microarrays and quantified the mRNA abundance using genome-wide expression arrays and miRNA abundance using next-generation sequencing. We reliably quantified 356 miRNA species that were expressed in human adipose tissue, a limited number of which made up most of the expressed miRNAs. We mapped the miRNA abundance as an expression quantitative trait and determined cis regulation of expression for nine of the miRNAs and of the processing of one miRNA (miR-28). The degree of genetic variation of miRNA expression was substantially less than that of mRNAs. For the majority of the miRNAs, genetic regulation of expression was independent of the expression of mRNA from which the miRNA is transcribed. We also showed that for 108 miRNAs, mapped reads displayed widespread variation from the canonical sequence. We found a total of 24 miRNAs to be significantly associated with MetSyn traits. We suggest a regulatory role for miR-204-5p which was predicted to inhibit acetyl coenzyme A carboxylase β, a key fatty acid oxidation enzyme that has been shown to play a role in regulating body fat and insulin resistance in adipose tissue.

Association of risk variants for type 2 diabetes and hyperglycemia with gestational diabetes

OBJECTIVE The aim of this study was to investigate the association of risk variants for type 2 diabetes (T2D) and hyperglycemia with gestational diabetes (GDM). DESIGN AND METHODS Five hundred and thirty-three Finnish women who were diagnosed with GDM and 407 controls with normal glucose tolerance during the pregnancy were genotyped for 69 single-nucleotide polymorphisms (SNPs) which have been previously verified as susceptibility risk variants for T2D and hyperglycemia. All participants underwent an oral glucose tolerance test at the follow-up study after the index pregnancy. RESULTS Risk variants rs10830963 and rs1387153 of MTNR1B were significantly associated with GDM (odds ratio (OR)=1.62 (95% CI 1.34-1.96), P=4.5 × 10⁻⁷ and 1.38 (1.14-1.66), P=7.6 × 10⁻⁴ respectively). Both SNPs of MTNR1B were also significantly associated with elevated fasting glucose level and reduced insulin secretion at follow-up. Additionally, risk variants rs9939609 of FTO, rs2796441 of TLE1, rs560887 of G6PC2, rs780094 of GCKR, rs7903146 of TCF7L2 and rs11708067 of ADCY5 showed nominally significant associations with GDM (OR range from 1.25 to 1.30). CONCLUSIONS Our study suggests that GDM and T2D share a similar genetic background. Our findings also provide further evidence that risk variants of MTNR1B are associated with GDM by increasing fasting plasma glucose and decreasing insulin secretion.

Association of Ketone Body Levels With Hyperglycemia and Type 2 Diabetes in 9,398 Finnish Men

We investigated the association of the levels of ketone bodies (KBs) with hyperglycemia and with 62 genetic risk variants regulating glucose levels or type 2 diabetes in the population-based Metabolic Syndrome in Men (METSIM) study, including 9,398 Finnish men without diabetes or newly diagnosed type 2 diabetes. Increasing fasting and 2-h plasma glucose levels were associated with elevated levels of acetoacetate (AcAc) and β-hydroxybutyrate (BHB). AcAc and BHB predicted an increase in the glucose area under the curve in an oral glucose tolerance test, and AcAc predicted the conversion to type 2 diabetes in a 5-year follow-up of the METSIM cohort. Impaired insulin secretion, but not insulin resistance, explained these findings. Of the 62 single nucleotide polymorphisms associated with the risk of type 2 diabetes or hyperglycemia, the glucose-increasing C allele of GCKR significantly associated with elevated levels of fasting BHB levels. Adipose tissue mRNA expression levels of genes involved in ketolysis were significantly associated with insulin sensitivity (Matsuda index). In conclusion, high levels of KBs predicted subsequent worsening of hyperglycemia, and a common variant of GCKR was significantly associated with BHB levels.

Limited Overlap Between Intermediate Hyperglycemia as Defined by A1C 5.7–6.4%, Impaired Fasting Glucose, and Impaired Glucose Tolerance

OBJECTIVE We compared the prevalences and overlap between intermediate hyperglycemia (IH), defined by a hemoglobin A1c (A1C) 5.7–6.4%, impaired fasting glucose (IFG), and impaired glucose tolerance (IGT). RESEARCH DESIGN AND METHODS Oral glucose tolerance test results and A1C measurements were evaluated as markers of IH in an unselected cohort of 486 nondiabetic adults from Finland. RESULTS The overall prevalence of IH was 34%. Prevalences of isolated A1C 5.7–6.4%, IGT, and IFG were 8.0, 13.2, and 4.5%, respectively. Overlap between these three markers was uncommon. Isolated A1C 5.7–6.4% was associated with a higher BMI compared with isolated IFG and IGT and with a more adverse lipid profile compared with isolated IFG. CONCLUSIONS Prevalence of isolated IH was high, with limited overlap between the definitions. Differences in cardiovascular disease risk factors were observed among the groups. This study demonstrates that an A1C of 5.7–6.4% detects, in part, different individuals with IH compared with IFG and IGT.

Unacylated ghrelin is associated with changes in body composition and body fat distribution during long-term exercise intervention

OBJECTIVE Ghrelin, a gut-brain peptide involved in energy homeostasis, circulates predominantly (>90%) in unacylated form. Previous studies, however, have focused on total and acylated ghrelin, and the role of unacylated ghrelin (UAG) is not well understood. Particularly, the association of UAG with weight loss and changes in body composition in adults remains unclear. We hypothesized that exercise-associated increase in UAG level is associated with weight loss, favorable changes in body composition, and body fat distribution. DESIGN AND METHODS A prospective study of 552 young men (mean age 19.3 and range 19-28 years) undergoing military service with structured 6-month exercise training program. Exercise performance, body composition, and biochemical measurements were obtained at baseline and follow-up. Association between changes in UAG levels and body composition and body fat distribution were evaluated. RESULTS An increase in UAG level during the exercise intervention was associated with reduced weight, fat mass (FM), fat percentage (fat %), and waist circumference, but not with fat-free mass. Inverse associations of changes in UAG level with changes in waist circumference and fat % were independent of weight at baseline, and changes in weight and exercise performance. Associations of changes in UAG level with waist circumference were significantly stronger than with fat % after the adjustment for confounding variables. CONCLUSION UAG is associated with changes in body weight and body composition during an intensive long-term exercise intervention in young men. The association of UAG levels with changes in central obesity was stronger than with total FM.