Alex S. F. Doney

Replication of Genome-Wide Association Signals in UK Samples Reveals Risk Loci for Type 2 Diabetes

The molecular mechanisms involved in the development of type 2 diabetes are poorly understood. Starting from genome-wide genotype data for 1924 diabetic cases and 2938 population controls generated by the Wellcome Trust Case Control Consortium, we set out to detect replicated diabetes association signals through analysis of 3757 additional cases and 5346 controls and by integration of our findings with equivalent data from other international consortia. We detected diabetes susceptibility loci in and around the genes CDKAL1, CDKN2A/CDKN2B, and IGF2BP2 and confirmed the recently described associations at HHEX/IDE and SLC30A8. Our findings provide insight into the genetic architecture of type 2 diabetes, emphasizing the contribution of multiple variants of modest effect. The regions identified underscore the importance of pathways influencing pancreatic beta cell development and function in the etiology of type 2 diabetes.

Meta-analysis of genome-wide association data and large-scale replication identifies additional susceptibility loci for type 2 diabetes

Genome-wide association (GWA) studies have identified multiple loci at which common variants modestly but reproducibly influence risk of type 2 diabetes (T2D). Established associations to common and rare variants explain only a small proportion of the heritability of T2D. As previously published analyses had limited power to identify variants with modest effects, we carried out meta-analysis of three T2D GWA scans comprising 10,128 individuals of European descent and ∼2.2 million SNPs (directly genotyped and imputed), followed by replication testing in an independent sample with an effective sample size of up to 53,975. We detected at least six previously unknown loci with robust evidence for association, including the JAZF1 (P = 5.0 × 10−14), CDC123-CAMK1D (P = 1.2 × 10−10), TSPAN8-LGR5 (P = 1.1 × 10−9), THADA (P = 1.1 × 10−9), ADAMTS9 (P = 1.2 × 10−8) and NOTCH2 (P = 4.1 × 10−8) gene regions. Our results illustrate the value of large discovery and follow-up samples for gaining further insights into the inherited basis of T2D.

Effect of Metformin on Mortality in Patients With Heart Failure and Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (DM) plus chronic heart failure (CHF) is a common but lethal combination and therapeutic options are limited. Metformin is perceived as being relatively contraindicated in this context, although mounting evidence indicates that it may be beneficial. This study was carried out to investigate the use of metformin therapy for treating patients with DM and CHF in a large population-based cohort study. The Health Informatics Centre-dispensed prescribing database for the population of Tayside, Scotland (population ∼400,000) was linked to the Diabetes Audit and Research in Tayside Scotland (DARTS) information system. Patients with DM and incident CHF from 1994 to 2003 receiving oral hypoglycemic agents but not insulin were identified. Cox regression was used to assess differences in all-cause mortality rates between patients prescribed metformin and patients prescribed sulfonylureas with adjustment for co-morbidities and other therapies. Four hundred twenty-two study subjects (mean ± SD 75.4 ± 0.5 years of age, 46.2% women) were identified: metformin monotherapy (n = 68, mean age 75.5 ± 1.1 years, 48.5% women), sulfonylurea monotherapy (n = 217, mean age 76.7 ± 0.7 years, 45.2% women), and combination (n = 137, mean age, 73.4 ± 0.7 years, 46.7% women). Fewer deaths occurred in metformin users, alone or in combination with sulfonylureas, compared to the sulfonylurea monotherapy cohort at 1 year (0.59, 95% confidence interval 0.36 to 0.96) and over long-term follow up (0.67, 95% confidence interval 0.51 to 0.88). In conclusion, this large observational data suggest that metformin may be beneficial in patients with CHF and DM. These findings need to be verified by a prospective clinical trial.

Genetic loci for retinal arteriolar microcirculation

Narrow arterioles in the retina have been shown to predict hypertension as well as other vascular diseases, likely through an increase in the peripheral resistance of the microcirculatory flow. In this study, we performed a genome-wide association study in 18,722 unrelated individuals of European ancestry from the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium and the Blue Mountain Eye Study, to identify genetic determinants associated with variations in retinal arteriolar caliber. Retinal vascular calibers were measured on digitized retinal photographs using a standardized protocol. One variant (rs2194025 on chromosome 5q14 near the myocyte enhancer factor 2C MEF2C gene) was associated with retinal arteriolar caliber in the meta-analysis of the discovery cohorts at genome-wide significance of P-value <5×10−8. This variant was replicated in an additional 3,939 individuals of European ancestry from the Australian Twins Study and Multi-Ethnic Study of Atherosclerosis (rs2194025, P-value = 2.11×10−12 in combined meta-analysis of discovery and replication cohorts). In independent studies of modest sample sizes, no significant association was found between this variant and clinical outcomes including coronary artery disease, stroke, myocardial infarction or hypertension. In conclusion, we found one novel loci which underlie genetic variation in microvasculature which may be relevant to vascular disease. The relevance of these findings to clinical outcomes remains to be determined.

Genetic risk factors for ischaemic stroke and its subtypes (the METASTROKE collaboration): a meta-analysis of genome-wide association studies.

Summary Background Various genome-wide association studies (GWAS) have been done in ischaemic stroke, identifying a few loci associated with the disease, but sample sizes have been 3500 cases or less. We established the METASTROKE collaboration with the aim of validating associations from previous GWAS and identifying novel genetic associations through meta-analysis of GWAS datasets for ischaemic stroke and its subtypes. Methods We meta-analysed data from 15 ischaemic stroke cohorts with a total of 12 389 individuals with ischaemic stroke and 62 004 controls, all of European ancestry. For the associations reaching genome-wide significance in METASTROKE, we did a further analysis, conditioning on the lead single nucleotide polymorphism in every associated region. Replication of novel suggestive signals was done in 13 347 cases and 29 083 controls. Findings We verified previous associations for cardioembolic stroke near PITX2 (p=2·8×10−16) and ZFHX3 (p=2·28×10−8), and for large-vessel stroke at a 9p21 locus (p=3·32×10−5) and HDAC9 (p=2·03×10−12). Additionally, we verified that all associations were subtype specific. Conditional analysis in the three regions for which the associations reached genome-wide significance (PITX2, ZFHX3, and HDAC9) indicated that all the signal in each region could be attributed to one risk haplotype. We also identified 12 potentially novel loci at p<5×10−6. However, we were unable to replicate any of these novel associations in the replication cohort. Interpretation Our results show that, although genetic variants can be detected in patients with ischaemic stroke when compared with controls, all associations we were able to confirm are specific to a stroke subtype. This finding has two implications. First, to maximise success of genetic studies in ischaemic stroke, detailed stroke subtyping is required. Second, different genetic pathophysiological mechanisms seem to be associated with different stroke subtypes. Funding Wellcome Trust, UK Medical Research Council (MRC), Australian National and Medical Health Research Council, National Institutes of Health (NIH) including National Heart, Lung and Blood Institute (NHLBI), the National Institute on Aging (NIA), the National Human Genome Research Institute (NHGRI), and the National Institute of Neurological Disorders and Stroke (NINDS).

Variation in TCF7L2 Influences Therapeutic Response to Sulfonylureas: A GoDARTs Study

OBJECTIVE— There is considerable interindividual variation in sulfonylurea response in type 2 diabetes. Transcription factor 7-like 2 (TCF7L2) variants have been identified to be strongly associated with type 2 diabetes risk, probably due to decreased β-cell function. We hypothesized that variation in TCF7L2 would influence response to sulfonylureas but not metformin. We studied the effect of TCF7L2 rs12255372 and rs7903146 genotypes on glycemic response. RESEARCH DESIGN AND METHODS— The DARTS/MEMO (Diabetes Audit and Research Tayside/Medicines Monitoring Unit) collaboration database includes prescribing, biochemistry, and clinical phenotype of all patients with diabetes within Tayside, Scotland, from 1992. Of these, the TCF7L2 genotype was determined in 4,469 patients with type 2 diabetes recruited to GoDARTS (Genetics of Diabetes Audit and Research Tayside) between 1997 and July 2006. A total of 901 incident sulfonylurea users and 945 metformin users were identified. A logistic regression was used with treatment failure defined as an A1C >7% within 3–12 months after treatment initiation. Covariates included the TCF7L2 genotype, BMI, sex, age diagnosed, drug adherence, and drug dose. A1C pretreatment was available in a subset of patients (sulfonylurea n = 579; metformin n = 755). RESULTS— Carriers of the risk allele were less likely to respond to sulfonylureas with an odds ratio (OR) for failure of 1.95 (95% CI 1.23–3.06; P = 0.005), comparing rs12255372 T/T vs. G/G. Including the baseline A1C strengthened this association (OR 2.16 [95% CI 1.21–3.86], P = 0.009). A similar, although slightly weaker, association was seen with rs7903146. No association was seen between metformin response and either single nucleotide polymorphism, after adjustment for baseline A1C. CONCLUSIONS— TCF7L2 variants influence therapeutic response to sulfonylureas but not metformin. This study establishes that genetic variation can alter response to therapy in type 2 diabetes.

Common nonsynonymous substitutions in SLCO1B1 predispose to statin intolerance in routinely treated individuals with Type 2 diabetes: A Go-DARTS study

SLCO1B1 gene variants are associated with severe statin‐induced myopathy. We examined whether these variants are also associated with general statin intolerance in a large population of patients with type 2 diabetes receiving statins as part of routine clinical care. A total of 4,196 individuals were genotyped for rs4149056 (Val174Ala) and rs2306283 (Asp130Asn). Intolerance was defined by serum biochemistry and also by discontinuation, switching, or reduction in dose of the prescribed statin drug. Ala174 was associated with higher intolerance (odds ratio = 2.05, P = 0.043), whereas Asp130 was associated with lower intolerance (odds ratio = 0.71, P = 0.026). Ala174 was associated with a lower low‐density lipoprotein cholesterol (LDLc) response to statins (P = 0.01) whereas 130D was associated with a greater LDLc response to statins (P = 0.048), as previously reported; however, this association was no longer present when data for statin‐intolerant individuals were removed from the analysis. This study suggests that common genetic variants selected for an extreme phenotype of statin‐induced myopathy also predispose to more common milder statin intolerance and may, for this reason, impact lipid‐lowering efficacy.

The cost of cerebral ischaemia

Cerebral ischaemia is a major cause of disability and death globally and has a profoundly negative impact on the individuals it affects, those that care for them and society as a whole. The most common and familiar manifestation is stroke, 85% of which are ischaemic and which is the second leading cause of death and most common cause of complex chronic disability worldwide. Stroke survivors often suffer from long-term neurological disabilities significantly reducing their ability to integrate effectively in society with all the financial and social consequences that this implies. These difficulties cascade to their next of kin who often become caregivers and are thus indirectly burdened. A more insidious consequence of cerebral ischaemia is progressive cognitive impairment causing dementia which although less abrupt is also associated with a significant long-term disability. Globally cerebrovascular diseases are responsible for 5.4 million deaths every year (1 in 10 of total). Approximately 3% of total healthcare expenditure is attributable to cerebral ischaemia with cerebrovascular diseases costing EU healthcare systems 21 billion euro in 2003. The cost to the wider economy (including informal care and lost productivity) is even greater with stroke costing the UK 7-8 billion pound in 2005 and the US

Reduced-Function SLC22A1 Polymorphisms Encoding Organic Cation Transporter 1 and Glycemic Response to Metformin: A GoDARTS Study

62.7 billion in 2007. Cerebrovascular disease cost the EU 34 billion euro in 2003. From 2005 to 2050 the anticipated cost of stroke to the US economy is estimated at

Haplotype analysis of the PPARγ Pro12Ala and C1431T variants reveals opposing associations with body weight

2.2 trillion. Given the global scale of the problem and the enormous associated costs it is clear that there is an urgent need for advances in the prevention of cerebral ischaemia and its consequences. Such developments would result in profound benefits for both individuals and their wider societies and address one of the worlds most pre-eminent public health issues.