Type 2 diabetes risk alleles near ADCY5, CDKAL1 and HHEX-IDE are associated with reduced birthweight

Aims/hypothesis

The fetal insulin hypothesis suggests that variation in the fetal genotype influencing insulin secretion or action may predispose to low birthweight and type 2 diabetes. We examined associations between 25 confirmed type 2 diabetes risk variants and birthweight in individuals from the Danish Inter99 population and in meta-analyses including Inter99 data and reported studies.

Methods

Midwife records from the Danish State Archives provided information on mother’s age and parity, as well as birthweight, length at birth and prematurity of the newborn in 4,744 individuals of the population-based Inter99 study. We genotyped 25 risk alleles showing genome-wide associations with type 2 diabetes.

Results

Birthweight was inversely associated with the type 2 diabetes risk alleles of ADCY5 rs11708067 (β?=??33 g [95% CI ?55, ?10], p?=?0.004) and CDKAL1 rs7756992 (β?=??22 g [95% CI ?43, ?1], p?=?0.04). The association for the latter locus was confirmed in a meta-analysis (n?=?24,885) (β?=??20 g [95% CI ?29, ?11], p?=?5?×?10^?6). The HHEX-IDE rs1111875 variant showed no significant association among Danes (p?=?0.09); however, in a meta-analysis (n?=?25,164) this type 2 diabetes risk allele was associated with lower birthweight (β?=??16 g [95% CI ?24, ?8], p?=?8?×?10^?5). On average, individuals with high genetic risk (≥25 type 2 diabetes risk alleles) weighed marginally less at birth than those with low genetic risk (<25 type 2 diabetes risk alleles) (β?=??35 g [95% CI ?69, ?2], p?=?0.037).

Conclusions/interpretation

We report a novel association between the fetal ADCY5 type 2 diabetes risk allele and decreased birthweight, and confirm in meta-analyses associations between decreased birthweight and the type 2 diabetes risk alleles of HHEX-IDE and CDKAL1. No strong general effect on birthweight can be ascribed to the 25 common type 2 diabetes risk alleles.     

Genetic variants at CDC123/CAMK1D and SPRY2 are associated with susceptibility to type 2 diabetes in the Japanese population

Aims/hypothesis

Recently, rs10906115 in CDC123/CAMK1D, rs1359790 near SPRY2, rs1436955 in C2CD4A/C2CD4B and rs10751301 in ODZ4 were identified as genetic risk variants for type 2 diabetes by a genome-wide association study in a Chinese population. The aim of the present study was to ascertain the role of these four variants in conferring susceptibility to type 2 diabetes in the Japanese population.

Methods

We genotyped 11,530 Japanese individuals (8,552 type 2 diabetes cases, 2,978 controls) for the above single nucleotide polymorphisms (SNPs) and used logistic regression analysis to determine whether they were associated with type 2 diabetes.

Results

In accordance with the findings in a Chinese population, rs10906115 A, rs1359790 C and rs1436955 G were found to be risk alleles. Both rs10906115 and rs1359790 were significantly associated with susceptibility to type 2 diabetes in our study (rs10906115 OR 1.15, 95% CI 1.08, 1.22; p?=?6.10?×?10^?6; rs1359790 OR 1.14, 95% CI 1.06, 1.21; p?=?2.24?×?10^?4). Adjustment for age, sex and BMI had no significant effects on the association between these variants and the disease. We did not observe any significant associations between the SNPs and any metabolic traits, e.g. BMI, fasting plasma glucose (determined for 1,332 controls), HOMA of beta cell function (900 controls) and HOMA of insulin resistance (900 controls; p?>?0.05).

Conclusions/interpretation

The SNPs rs10906115 A and rs1359790 C are significantly associated with susceptibility to type 2 diabetes in the Japanese population, confirming that these alleles are common susceptibility variants for type 2 diabetes in East Asian populations.     

Decreased insulin secretion and increased risk of type 2 diabetes associated with allelic variations of the WFS1 gene: the Data from Epidemiological Study on the Insulin Resistance Syndrome (DESIR) prospective study

Aims/hypothesis

We investigated associations of allelic variations in the WFS1 gene with insulin secretion and risk of type 2 diabetes in a general population prospective study.

Methods

We studied 5,110 unrelated French men and women who participated in the prospective Data from Epidemiological Study on the Insulin Resistance Syndrome (DESIR) study. Additional cross-sectional analyses were performed on 4,472 French individuals with type 2 diabetes and 3,065 controls. Three single nucleotide polymorphisms (SNPs) were genotyped: rs10010131, rs1801213/rs7672995 and rs734312.

Results

We observed statistically significant associations between the major alleles of the three variants and prevalent type 2 diabetes in the DESIR cohort at baseline. Cox analyses showed an association between the G-allele of rs10010131 and incident type 2 diabetes (HR 1.34, 95% CI 1.08?C1.70, p?=?0.007). Similar results were observed for the G-allele of rs1801213 and the A-allele of rs734312. The GGA haplotype was associated with an increased risk of diabetes as compared with the ACG haplotype (HR 1.26, 95% CI 1.04?C1.42, p?=?0.02). We also observed statistically significant associations of the three SNPs with plasma glucose, HbA_1c levels and insulin secretion at baseline and throughout the study in individuals with type 2 diabetes or at risk of developing diabetes. However, no association was observed in those who remained normoglycaemic at the end of the follow-up. Associations between the three variants and type 2 diabetes were replicated in cross-sectional studies of type 2 diabetic patients in comparison with a non-diabetic control group.

Conclusions/interpretation

The most frequent haplotype at the haplotype block containing the WFS1 gene modulated insulin secretion and was associated with an increased risk of type 2 diabetes.     

Systematic evaluation of validated type 2 diabetes and glycaemic trait loci for association with insulin clearance

Aims/hypothesis

Insulin clearance is a highly heritable trait, for which few quantitative trait loci have been discovered. We sought to determine whether validated type 2 diabetes and/or glycaemic trait loci are associated with insulin clearance.

Methods

Hyperinsulinaemic–euglycaemic clamps were performed in two Hispanic-American family cohorts totalling 1329 participants in 329 families. The Metabochip was used to fine-map about 50 previously identified loci for type 2 diabetes, fasting glucose, fasting insulin, 2 h glucose or HbA_1c. This resulted in 17,930 variants, which were tested for association with clamp-derived insulin clearance via meta-analysis of the two cohorts.

Results

In the meta-analysis, 38 variants located within seven loci demonstrated association with insulin clearance (p?<?0.001). The top signals for each locus were rs10241087 (DGKB/TMEM195 [TMEM195 also known as AGMO]) (p?=?4.4?×?10^?5); chr1:217605433 (LYPLAL1) (p?=?3.25?×?10^?4); rs2380949 (GLIS3) (p?=?3.4?×?10^?4); rs55903902 (FADS1) (p?=?5.6?×?10^?4); rs849334 (JAZF1) (p?=?6.4?×?10^?4); rs35749 (IGF1) (p?=?6.7?×?10^?4); and rs9460557 (CDKAL1) (p?=?6.8?×?10^?4).

Conclusions/interpretation

While the majority of validated loci for type 2 diabetes and related traits do not appear to influence insulin clearance in Hispanics, several of these loci do show evidence of association with this trait. It is therefore possible that these loci could have pleiotropic effects on insulin secretion, insulin sensitivity and insulin clearance.     

Common variant in the HMGA2 gene increases susceptibility to nephropathy in patients with type 2 diabetes

Aims/hypothesis

Type 2 diabetes is a chronic metabolic disorder associated with devastating microvascular complications. Genome-wide association studies have identified more than 60 genetic variants associated with type 2 diabetes and/or glucose and insulin traits, but their role in the progression of diabetes is not established. The aim of this study was to explore whether these variants were also associated with the development of nephropathy in patients with type 2 diabetes.

Methods

We studied 28 genetic variants in 2,229 patients with type 2 diabetes from the local Malmö Scania Diabetes Registry (SDR) published during 2007–2010. Diabetic nephropathy (DN) was defined as micro- or macroalbuminuria and/or end-stage renal disease. Estimated glomerular filtration rate (eGFR) was assessed using the MDRD-4 formula. Replication genotyping of rs1531343 was performed in diabetic (Steno type 2 diabetes [n?=?345], Genetics of Diabetes Audit and Research in Tayside Scotland [Go-DARTS] [n?=?784]) and non-diabetic (Malmö Preventive Project [n?=?2,523], Botnia study [n?=?2,247]) cohorts.

Results

In the SDR, HMGA2 single-nucleotide polymorphism rs1531343 was associated with DN (OR 1.50, 95% CI 1.20, 1.87, p?=?0.00035). In the combined analysis totalling 3,358 patients with type 2 diabetes (n?=?1,233 cases, n?=?2,125 controls), carriers of the C-allele had a 1.45-fold increased risk of developing nephropathy (95% CI 1.20, 1.75, p?=?0.00010). Furthermore, the risk C-allele was associated with lower eGFR in patients with type 2 diabetes (n?=?2,499, β?±?SEM, ?3.7?±?1.2 ml/min, p?=?0.002) and also in non-diabetic individuals (n?=?17,602, β?±?SEM, ?0.008?±?0.003 ml/min (log _e ), p?=?0.006).

Conclusions/interpretation

These data demonstrate that the HMGA2 variant seems to be associated with increased risk of developing nephropathy in patients with type 2 diabetes and lower eGFR in both diabetic and non-diabetic individuals and could thus be a common denominator in the pathogenesis of type 2 diabetes and kidney complications.     

Type 2 diabetes susceptibility gene variants predispose to adult-onset autoimmune diabetes

Aims/hypothesis

Latent autoimmune diabetes in adults (LADA) is phenotypically a hybrid of type 1 and type 2 diabetes. Genetically LADA is poorly characterised but does share genetic predisposition with type 1 diabetes. We aimed to improve the genetic characterisation of LADA and hypothesised that type 2 diabetes-associated gene variants also predispose to LADA, and that the associations would be strongest in LADA patients with low levels of GAD autoantibodies (GADA).

Methods

We assessed 41 type 2 diabetes-associated gene variants in Finnish (phase I) and Swedish (phase II) patients with LADA (n?=?911) or type 1 diabetes (n?=?406), all diagnosed after the age of 35 years, as well as in non-diabetic control individuals 40 years or older (n?=?4,002).

Results

Variants in the ZMIZ1 (rs12571751, p?=?4.1?×?10^?5) and TCF7L2 (rs7903146, p?=?5.8?×?10^?4) loci were strongly associated with LADA. Variants in the KCNQ1 (rs2237895, p?=?0.0012), HHEX (rs1111875, p?=?0.0024 in Finns) and MTNR1B (rs10830963, p?=?0.0039) loci showed the strongest association in patients with low GADA, supporting the hypothesis that the disease in these patients is more like type 2 diabetes. In contrast, variants in the KLHDC5 (rs10842994, p?=?9.5?×?10^?4 in Finns), TP53INP1 (rs896854, p?=?0.005), CDKAL1 (rs7756992, p?=?7.0?×?10^?4; rs7754840, p?=?8.8?×?10^?4) and PROX1 (rs340874, p?=?0.003) loci showed the strongest association in patients with high GADA. For type 1 diabetes, a strong association was seen for MTNR1B (rs10830963, p?=?3.2?×?10^?6) and HNF1A (rs2650000, p?=?0.0012).

Conclusions/interpretation

LADA and adult-onset type 1 diabetes share genetic risk variants with type 2 diabetes, supporting the idea of a hybrid form of diabetes and distinguishing them from patients with classical young-onset type 1 diabetes.     

A common genetic variant in WFS1 determines impaired glucagon-like peptide-1-induced insulin secretion

Aims/hypothesis

WFS1 type 2 diabetes risk variants appear to be associated with impaired beta cell function, although it is unclear whether insulin secretion is affected directly or secondarily via alteration of insulin sensitivity. We aimed to investigate the effect of a common WFS1 single-nucleotide polymorphism on several aspects of insulin secretion.

Methods

A total of 1,578 non-diabetic individuals (534 men and 1,044 women, aged 40?±?13 years, BMI 28.9?±?8.2 kg/m² [mean ± SD]) at increased risk of type 2 diabetes were genotyped for rs10010131 within the WFS1 gene. All participants underwent an OGTT (and a subset additionally an IVGTT [n?=?319]) and a hyperglycaemic clamp combined with glucagon-like peptide-1 (GLP-1) and arginine stimuli (n?=?102).

Results

rs10010131 was associated with reduced OGTT-derived insulin secretion (p?=?0.03). In contrast, insulin secretion induced by an i.v. glucose challenge in the IVGTT and hyperglycaemic clamp was not different between the genotypes. GLP-1 infusion combined with a hyperglycaemic clamp showed a significant reduction of the insulin secretion rate during the first and second phases of GLP-1-induced insulin secretion in carriers of the risk allele (reduction of 36% and 26%, respectively; p?=?0.007 and p?=?0.04, respectively).

Conclusions/interpretation

A common genetic variant in WFS1 specifically impairs GLP-1-induced insulin secretion independently of insulin sensitivity. This defect might explain the impaired insulin secretion in carriers of the risk allele and confer the increased risk of type 2 diabetes.     

Association of genetic variants of NOS1AP with type 2 diabetes in a Chinese population

Aims/hypothesis

Chromosome 1q21-q24 has been shown to be linked to type 2 diabetes. The International Type 2 Diabetes 1q Consortium showed that one of the nominal associations was located in the NOS1AP gene. Although this association was not replicated in additional samples of European descent, it remains unknown whether NOS1AP plays a role in Chinese individuals.

Methods

In stage 1 analyses, 79 single nucleotide polymorphisms (SNPs) of the NOS1AP gene were successfully genotyped in a group of Shanghai Chinese individuals, comprising 1,691 type 2 diabetes patients and 1,720 control participants. In stage 2 analyses, the SNP showing the strongest association was genotyped in additional Chinese individuals, including 1,663 type 2 diabetes patients and 1,408 control participants.

Results

In stage 1 analyses, 20 SNPs were nominally associated with type 2 diabetes (p?<?0.05), with SNP rs12742393 showing the strongest association (OR 1.24 [95% CI 1.11–1.38]; p?=?0.0002, empirical p?=?0.019). Haplotype analysis also confirmed the association between rs12742393 and type 2 diabetes. In stage 2 analyses, the difference in allele frequency distribution of rs12742393 did not reach statistical significance (p?=?0.254). However, the meta-analysis showed a significant association between rs12742393 and type 2 diabetes with an OR of 1.17 (95% CI 1.07–1.26; p?=?0.0005).

Conclusions/interpretation

Our data suggest that NOS1AP variants may not play a dominant role in susceptibility to type 2 diabetes, but a minor effect cannot be excluded.     

Glucose tolerance, insulin sensitivity and insulin release in European non-diabetic carriers of a polymorphism upstream of CDKN2A and CDKN2B

Aims/hypothesis

The aim of this study was to investigate the association of the rs10811661 polymorphism near the CDKN2B/CDKN2A genes with glucose tolerance, insulin sensitivity and insulin release in three samples of white people with European ancestry.

Methods

Sample 1 comprised 845 non-diabetic offspring of type 2 diabetes patients recruited in five European centres participating in the EUGENE2 study. Samples 2 and 3 comprised, respectively, 864 and 524 Italian non-diabetic participants. All individuals underwent an OGTT. Screening for the rs10811661 polymorphism was performed using a TaqMan allelic discrimination assay.

Results

The rs10811661 polymorphism did not show a significant association with age, BMI and insulin sensitivity. Participants carrying the TT genotype showed a significant reduction in insulin release, measured by an OGTT-derived index, compared with carriers of the C allele, in the three samples. When these results were pooled with those of three published studies, and meta-analysed with a random-effects model, the T allele was significantly associated with reduced insulin secretion (?35.09 [95% CI 14.68?C55.52], p?=?0.0008 for CC+CT vs TT; and ?29.45 [95% CI 9.51?C49.38], p?=?0.0038, for the additive model). In addition, in our three samples, participants carrying the TT genotype exhibited an increased risk for impaired glucose tolerance (IGT) compared with carriers of the C allele (OR 1.55 [95% CI 1.20?C1.95] for the meta-analysis of the three samples).

Conclusions/interpretation

Our data, together with the meta-analysis of previously published studies, show that the rs10811661 polymorphism is associated with impaired insulin release and IGT, suggesting that this variant may contribute to type 2 diabetes by affecting beta cell function.     

Variants associated with type 2 diabetes identified by the transethnic meta-analysis study: assessment in American Indians and evidence for a new signal in LPP

Aim/hypothesis

A recent genome-wide trans-ancestry meta-analysis identified seven new loci associated with type 2 diabetes. We assessed the replication of the seven lead single nucleotide polymorphisms (SNPs) and evaluated these loci for additional signals in American Indians.

Methods

Seven SNPs were genotyped in 7,710 individuals from a longitudinally studied American Indian population, and associations with type 2 diabetes, BMI and related phenotypes were assessed. Previous genome-wide association study (GWAS) data from these individuals were used to screen for additional type 2 diabetes signals at these loci. A variant independent of the trans-ancestry meta-analysis was identified within LPP, and its replication was assessed in an additional 3,106 urban American Indians.

Results

SNP rs6813195 near to TMEM154 was nominally associated with type 2 diabetes (p?=?0.01, OR 1.12 [95% CI 1.03, 1.22]) and adiposity: the type 2 diabetes risk allele was associated with a lower percentage body fat (β?=??1.451%, p?=?4.8?×?10^?4). Another SNP, rs3130501 near to POU5F1–TCF19, was associated with BMI (β?=??0.012, p?=?0.004), type 2 diabetes adjusted for BMI (p?=?0.02, OR 1.11 [95% CI 1.02, 1.22]), 2 h glucose concentrations (β?=?0.080 mmol/l, p?=?0.02) and insulin resistance estimated by homeostatic model (β?=?0.039, p?=?0.009). The independent variant identified at the LPP locus in our American Indian GWAS for type 2 diabetes was replicated in the additional samples (all American Indian meta-analysis, p?=?8.9?×?10^?6, OR 1.29 [95% CI 1.15, 1.45]).

Conclusions/interpretation

For two of the seven newly identified variants, there was nominal evidence for association with type 2 diabetes and related traits in American Indians. Identification of an independent variant at the LPP locus suggests the existence of more than one type 2 diabetes signal at this locus.     

A variant in the G6PC2/ABCB11 locus is associated with increased fasting plasma glucose, increased basal hepatic glucose production and increased insulin release after oral and intravenous glucose loads

Aims/hypothesis

An association between elevated fasting plasma glucose and the common rs560887 G allele in the G6PC2/ABCB11 locus has been reported. In Danes we aimed to examine rs560887 in relation to plasma glucose and serum insulin responses following oral and i.v. glucose loads and in relation to hepatic glucose production during a hyperinsulinaemic–euglycaemic clamp. Furthermore, we examined rs560887 for association with impaired fasting glycaemia (IFG), impaired glucose tolerance (IGT), type 2 diabetes and components of the metabolic syndrome.

Methods

rs560887 was genotyped in the Inter99 cohort (n?=?5,899), in 366 young, healthy Danes, in non-diabetic relatives of type 2 diabetic patients (n?=?196), and in young and elderly twins (n?=?159). Participants underwent an OGTT, an IVGTT or a 2 h hyperinsulinaemic–euglycaemic clamp.

Results

The rs560887 G allele associated with elevated fasting plasma glucose (p?=?2?×?10^?14) but not with plasma glucose levels at 30 min (p?=?0.9) or 120 min (p?=?0.9) during an OGTT. G allele carriers had elevated levels of serum insulin at 30 min during an OGTT (p?=?1?×?10^?4) and relatives of type 2 diabetes patients carrying the G allele had an increased acute insulin response (p?=?4?×?10^?4) during an IVGTT. Among elderly twins, G allele carriers had higher basal hepatic glucose production (p?=?0.04). Finally, the G allele associated with the risk of having IFG (OR 1.26, 95% CI 1.08–1.47, p?=?0.002), but not with IGT (OR 0.94, 95% CI 0.82–1.08, p?=?0.4) or type 2 diabetes (OR 0.93, 95% CI 0.84–1.04, p?=?0.2).

Conclusions/interpretation

The common rs560887 G allele in the G6PC2/ABCB11 locus is associated with increased fasting glycaemia and increased risk of IFG, associations that may be partly related to an increased basal hepatic glucose production rate.     

Homozygous carriers of the G allele of rs4664447 of the glucagon gene (GCG) are characterised by decreased fasting and stimulated levels of insulin, glucagon and glucagon-like peptide (GLP)-1

Aims/hypothesis

The glucagon gene (GCG) encodes several hormones important for energy metabolism: glucagon, oxyntomodulin and glucagon-like peptide (GLP)-1 and -2. Variants in GCG may associate with type 2 diabetes, obesity and/or related metabolic traits.

Methods

GCG was re-sequenced as a candidate gene in 865 European individuals. Twenty-nine variants were identified. Four variants that were considered to have a likelihood for altered functionality: rs4664447, rs7581952, Ile158Val and Trp169Ter, were genotyped in 17,584 Danes.

Results

When examined in 5,760 treatment-naive individuals, homozygous carriers of the low frequency (minor allele frequency 2.3%) G allele of rs4664447, predicted to disrupt an essential splice enhancer binding site, had lower levels of fasting plasma glucose (mean?±?SD, 4.8?±?1.2 vs 5.5?±?0.8?mmol/l, p?=?0.004); fasting serum insulin (22?±?14 vs 42?±?27?pmol/l, p?=?0.04); glucose-stimulated serum insulin (159?±?83 vs 290?±?183?pmol/l, p?=?0.01) and adult height (165?±?10 vs 172?±?9?cm, p?=?0.0009) compared with A allele carriers. During oral glucose tolerance and hyperglycaemic arginine stimulation tests, the plasma AUC for GLP-1 (730?±?69 vs 1,334?±?288?pmol/l?×?min, p?=?0.0002) and basal and stimulated levels of serum insulin and plasma glucagon were ??50% decreased (p?Conclusions/interpretation Re-sequencing of GCG revealed a low frequency intronic variant, rs4664447, and follow-up physiological studies suggest that this variant in homozygous form may cause decreased fasting and stimulated levels of insulin, glucagon and GLP-1. Overall, our findings suggest that variation in GCG has no major impact on carbohydrate metabolism in the study populations examined.     

Sleep duration does not mediate or modify association of common genetic variants with type 2 diabetes

Aims/hypothesis

Short and long sleep duration are associated with increased risk of type 2 diabetes. We aimed to investigate whether genetic variants for fasting glucose or type 2 diabetes associate with short or long sleep duration and whether sleep duration modifies the association of genetic variants with these traits.

Methods

We examined the cross-sectional relationship between self-reported habitual sleep duration and prevalence of type 2 diabetes in individuals of European descent participating in five studies included in the Candidate Gene Association Resource (CARe), totalling 1,474 cases and 8,323 controls. We tested for association of 16 fasting glucose-associated variants, 27 type 2 diabetes-associated variants and aggregate genetic risk scores with continuous and dichotomised (≤5 h or ≥9 h) sleep duration using regression models adjusted for age, sex and BMI. Finally, we tested whether a gene × behaviour interaction of variants with sleep duration had an impact on fasting glucose or type 2 diabetes risk.

Results

Short sleep duration was significantly associated with type 2 diabetes in CARe (OR 1.32; 95% CI 1.08, 1.61; p?=?0.008). Variants previously associated with fasting glucose or type 2 diabetes and genetic risk scores were not associated with sleep duration. Furthermore, no study-wide significant interaction was observed between sleep duration and these variants on glycaemic traits. Nominal interactions were observed for sleep duration and PPARG rs1801282, CRY2 rs7943320 and HNF1B rs4430796 in influencing risk of type 2 diabetes (p?<?0.05).

Conclusions/interpretation

Our findings suggest that differences in habitual sleep duration do not mediate or modify the relationship between common variants underlying glycaemic traits (including in circadian rhythm genes) and diabetes.     

Association of genetic predisposition to obesity with type 2 diabetes risk in Han Chinese individuals

Aims/hypothesis

Obesity is a major risk factor for type 2 diabetes, but little is known about the contribution of BMI-associated loci to type 2 diabetes risk in East Asian populations.

Methods

In this study, 30 known BMI-associated variants and a genetic risk score (GRS) calculated by summing the BMI-increasing alleles of these variants were tested for associations with type 2 diabetes and related glycaemic traits in 1,873 cases of type 2 diabetes and 1,839 controls in Han Chinese individuals. Logistic and linear regression analyses were performed to determine the association with type 2 diabetes risk or related glycaemic traits, respectively, under an additive model with or without adjustment for BMI.

Results

The GRS was significantly associated with increased BMI (β [SE] 0.070 [0.016]; p?=?1.33?×?10^?5) in the overall population. Each additional BMI-increasing allele in the GRS increased type 2 diabetes risk by 1.029-fold (95% CI 1.008, 1.050; p?=?0.0056) without adjustment for BMI, and the association was slightly attenuated after adjustment for BMI (OR 1.022; 95% CI 1.002, 1.043; p?=?0.035). In non-diabetic controls, the GRS was also associated with HOMA of beta cell function (HOMA-B) with adjustment for BMI (β [SE] ?0.876 [0.345]; p?=?0.011). Notably, the association of GRS with type 2 diabetes was abolished after adjusting for HOMA-B (OR 1.012; 95% CI 0.986, 1.039; p?=?0.380).

Conclusions/interpretation

Our results suggested that genetic predisposition to obesity leads to increased risk of type 2 diabetes, independent of BMI and partly through impaired beta cell function.     

Genetic association analysis of LARS2 with type 2 diabetes

Aims/hypothesis

LARS2 has been previously identified as a potential type 2 diabetes susceptibility gene through the low-frequency H324Q (rs71645922) variant (minor allele frequency [MAF] 3.0%). However, this association did not achieve genome-wide levels of significance. The aim of this study was to establish the true contribution of this variant and common variants in LARS2 (MAF?>?5%) to type 2 diabetes risk.

Methods

We combined genome-wide association data (n?=?10,128) from the DIAGRAM consortium with independent data derived from a tagging single nucleotide polymorphism (SNP) approach in Dutch individuals (n?=?999) and took forward two SNPs of interest to replication in up to 11,163 Dutch participants (rs17637703 and rs952621). In addition, because inspection of genome-wide association study data identified a cluster of low-frequency variants with evidence of type 2 diabetes association, we attempted replication of rs9825041 (a proxy for this group) and the previously identified H324Q variant in up to 35,715 participants of European descent.

Results

No association between the common SNPs in LARS2 and type 2 diabetes was found. Our replication studies for the two low-frequency variants, rs9825041 and H324Q, failed to confirm an association with type 2 diabetes in Dutch, Scandinavian and UK samples (OR 1.03 [95% CI 0.95–1.12], p?=?0.45, n?=?31,962 and OR 0.99 [0.90–1.08], p?=?0.78, n?=?35,715 respectively).

Conclusions/interpretation

In this study, the largest study examining the role of sequence variants in LARS2 in type 2 diabetes susceptibility, we found no evidence to support previous data indicating a role in type 2 diabetes susceptibility.     

A family history of diabetes is associated with reduced physical fitness in the Prevalence, Prediction and Prevention of Diabetes (PPP)–Botnia study

Aims/hypothesis

We studied the impact of a family history of type 2 diabetes on physical fitness, lifestyle factors and diabetes-related metabolic factors.

Methods

The Prevalence, Prediction and Prevention of Diabetes (PPP)–Botnia study is a population-based study in Western Finland, which includes a random sample of 5,208 individuals aged 18 to 75 years identified through the national Finnish Population Registry. Physical activity, dietary habits and family history of type 2 diabetes were assessed by questionnaires and physical fitness by a validated 2 km walking test. Insulin secretion and action were assessed based upon OGTT measurements of insulin and glucose.

Results

A family history of type 2 diabetes was associated with a 2.4-fold risk of diabetes and lower physical fitness (maximal aerobic capacity 29.2?±?7.2 vs 32.1?±?7.0, p?=?0.01) despite having similar reported physical activity to that of individuals with no family history. The same individuals also had reduced insulin secretion adjusted for insulin resistance, i.e. disposition index (p?<?0.001) despite having higher BMI (27.4?±?4.6 vs 26.0?±?4.3 kg/m², p?<?0.001).

Conclusions/interpretation

Individuals with a family history of type 2 diabetes are characterised by lower physical fitness, which cannot solely be explained by lower physical activity. They also have an impaired capacity of beta cells to compensate for an increase in insulin resistance imposed by an increase in BMI. These defects should be important targets for interventions aiming at preventing type 2 diabetes in individuals with inherited susceptibility to the disease.     

The human L-type calcium channel Cav1.3 regulates insulin release and polymorphisms in CACNA1D associate with type 2 diabetes

Aims/hypothesis

Voltage-gated calcium channels of the L-type have been shown to be essential for rodent pancreatic beta cell function, but data about their presence and regulation in humans are incomplete. We therefore sought to elucidate which L-type channel isoform is functionally important and its association with inherited diabetes-related phenotypes.

Methods

Beta cells of human islets from cadaver donors were enriched using FACS to study the expression of the genes encoding voltage-gated calcium channel (Ca_v)1.2 and Ca_v1.3 by absolute quantitative PCR in whole human and rat islets, as well as in clonal cells. Single-cell exocytosis was monitored as increases in cell capacitance after treatment with small interfering (si)RNA against CACNA1D (which encodes Ca_v1.3). Three single nucleotide polymorphisms (SNPs) were genotyped in 8,987 non-diabetic and 2,830 type 2 diabetic individuals from Finland and Sweden and analysed for associations with type 2 diabetes and insulin phenotypes.

Results

In FACS-enriched human beta cells, CACNA1D mRNA expression exceeded that of CACNA1C (which encodes Ca_v1.2) by approximately 60-fold and was decreased in islets from type 2 diabetes patients. The latter coincided with diminished secretion of insulin in vitro. CACNA1D siRNA reduced glucose-stimulated insulin release in INS-1 832/13 cells and exocytosis in human beta cells. Phenotype/genotype associations of three SNPs in the CACNA1D gene revealed an association between the C allele of the SNP rs312480 and reduced mRNA expression, as well as decreased insulin secretion in vivo, whereas both rs312486/G and rs9841978/G were associated with type 2 diabetes.

Conclusion/interpretation

We conclude that the L-type calcium channel Ca_v1.3 is important in human glucose-induced insulin secretion, and common variants in CACNA1D might contribute to type 2 diabetes.