Mary C Wallace

ABCG2 loss-of-function polymorphism predicts poor response to allopurinol in patients with gout

Many patients fail to achieve the recommended serum urate (SU) target (<6 mgdl−1) with allopurinol. The aim of our study was to examine the association of ABCG2 with SU target in response to standard doses of allopurinol using a cohort with confirmed adherence. Good response was defined as SU<6 mgdl−1 on allopurinol ⩽300 mgd−1 and poor response as SU⩾6 mgdl−1 despite allopurinol >300 mgd−1. Adherence was confirmed by oxypurinol concentrations. ABCG2 genotyping was performed using pre-designed single nucleotide polymorphism (SNP) TaqMan assays. Of 264 patients, 120 were good responders, 68 were poor responders and 76 were either non-adherent or could not be classified. The minor allele of ABCG2 SNP rs2231142 conferred a significantly increased risk of poor response to allopurinol (odds ratio=2.71 (1.70–4.48), P=6.0 × 10−5). This association remained significant after adjustment for age, sex, body mass index, ethnicity, estimated glomerular filtration rate, diuretic use and SU off urate-lowering therapy. ABCG2 rs2231142 predicts poor response to allopurinol, as defined by SU⩾6 mgdl−1 despite allopurinol >300 mgd−1.

Prevalence of HLA-B27 in the New Zealand population: effect of age and ethnicity

IntroductionHLA-B27 genotyping is commonly used to support a diagnosis of ankylosing spondylitis (AS). A recent study has suggested that HLA-B27 may adversely affect longevity. The objectives of this study were to determine, for the first time, the prevalence of HLA-B27 in the New Zealand population, and to test whether HLA-B27 prevalence declines with age.Methods117 Caucasian controls, 111 New Zealand Māori controls, and 176 AS patients were directly genotyped for HLA-B27 using PCR-SSP. These participants and a further 1103 Caucasian controls were genotyped for the HLA-B27 tagging single nucleotide polymorphisms (SNPs) rs4349859 and rs116488202. All AS patients testing positive for HLA-B27 of New Zealand Māori ancestry underwent high resolution typing to determine sub-allele status.ResultsHLA-B27 prevalence was 9.2% in New Zealand Caucasian controls and 6.5% in Māori controls. No decline in HLA-B27 prevalence with age was detected in Caucasian controls (p = 0.92). Concordance between HLA-B27 and SNP genotypes was 98.7-99.3% in Caucasians and 76.9-86% in Māori. Of the 14 AS patients of Māori ancestry, 1 was negative for HLA-B27, 10 were positive for HLAB*2705, and 3 positive for HLAB*2704. All cases of genotype discordance were explained by the presence of HLAB*2704.ConclusionsHLA-B27 prevalence in New Zealand Caucasians is consistent with that of Northern European populations and did not decline with increasing age. In Māori with AS who were HLA-B27 positive, 76.9% were positive for HLA-B*2705, suggesting that genetic susceptibility to AS in Māori is primarily due to admixture with Caucasians.

A human leukocyte antigen locus haplotype confers risk for allopurinol-related adverse effects in Caucasian patients with gout.

A human leukocyte antigen haplotype comprising six single-nucleotide polymorphisms (SNPs) confers risk for allopurinol hypersensitivity syndrome in Caucasians. The objective of the current study was to test for association of this haplotype with other, less severe adverse effects (AEs) of allopurinol therapy in a large New Zealand gout cohort. A total of 626 Caucasian and 766 Polynesian patients were genotyped for six SNPs (rs2844665, rs9263715, rs3130931, rs3130501, rs3094188, rs9469003) using TaqMan SNP assays. The CACGAC haplotype occurred at a frequency of 0.018 in Caucasians and 0.009 in Polynesians. The CACGAC haplotype occurred at a significantly higher frequency in Caucasian patients who experienced allopurinol-related AEs (13.3 vs. 1.7%, P=8.9e−06, odds ratio=8.9, 95% confidence interval 2.8–27.9), but it was not associated with overall allopurinol toxicity in Polynesians (P>0.05). Our study is the first to demonstrate the potential utility of this six-SNP haplotype as a predictor of milder allopurinol AEs.

PACSIN2 Does Not Influence Thiopurine-Related Toxicity In Patients With Inflammatory Bowel Disease

PACSIN2 Does Not Influence Thiopurine-Related Toxicity In Patients With Inflammatory Bowel Disease

Plasma oxypurinol as a measure of adherence in clinical trials

Adherence to urate-lowering therapy (ULT) in people with gout is often poor. A recent systematic review revealed 10%–46% of people with gout adhere to treatment.1 Among chronic diseases, gout has particularly low adherence rates.2 Adherence in clinical trials of ULT is a particularly important issue, as the primary efficacy endpoint for most studies (including phase III studies that form the basis of regulatory approval) is the ability of the agent to reduce serum urate (SU). Pill count-based adherence ≥80% is frequently regarded as an appropriate cut-off for good adherence; however, this is an indirect measure. Measurement of drug concentration may be an improved measure of the adherence.3 The aim of this study was to establish the relationship between two different measures of adherence and SU endpoints in a clinical trial of allopurinol in gout. Data, including demographics, SU, estimated glomerular filtration rate (eGFR), and plasma oxypurinol and allopurinol concentrations were available from a single study visit, and cumulative pill counts from the entire study period were available for 395 …

Identification of a novel thiopurine S-methyltransferase allele (TPMT*37).

Thiopurine S-methyltransferase (TPMT) is a key enzyme in the methylation of the thiopurine drugs azathioprine and 6-mercaptopurine. TPMT is subject to genetic polymorphism that results in a trimodal distribution of enzyme activity. All poor methylators (PMs) and 30-60% of intermediate methylators develop potentially life-threatening myelosuppression on standard doses of azathioprine and 6-mercaptopurine because of excess production of the thioguanine nucleotides (6-TGNs). Over 95% of PMs are explained by the alleles TPMT*2 and TPMT*3, whereas one in 20 intermediate methylators are heterozygous for a novel PM allele. In this brief report, we describe the identification of a novel allele (TPMT*37) in a Caucasian male who had a red blood cell TPMT activity of 8.9 U/ml (reference range: 9.3-17.6 U/ml). TPMT*37 introduces a premature stop codon at position 216, resulting in loss of the last 29 amino acid residues from the C terminal of the TPMT protein.

Association between ABCG2 rs2231142 and poor response to allopurinol: replication and meta-analysis

Objective ABCG2 rs2231142 (Q141K) has been reported to be associated with poor response to allopurinol, while there are conflicting data on the association between the genetically independent ABCG2 rs10011796 variant and allopurinol response. The aim of this study was to replicate the association of ABCG2 rs2231142 and rs10011796 with allopurinol response and perform a meta-analysis. Methods Participants in the Long-term Allopurinol Safety Study Evaluating Outcomes in Gout Patients (LASSO) (n = 299) were studied. In patients with evidence of adherence to allopurinol therapy (plasma oxypurinol >20 μmol/l), good response was defined as serum urate <6 mg/dl on allopurinol ⩽300 mg/day and poor response as serum urate ⩾ 6 mg/dl despite allopurinol >300 mg/day. Association of rs2231142 and rs10011796 with poor response was tested in logistic regression models that included age, sex, BMI, ethnicity and estimated glomerular filtration rate. Results from the LASSO study and a subset of participants in the Genetics of Gout in Aotearoa New Zealand study (n = 296, including 264 from a previously published report) were combined by meta-analysis. Results There was evidence for association of rs2231142 with allopurinol response [odds ratio (OR) = 2.35, P = 7.3 × 10-4] but not for rs10011796 (OR = 1.21, P = 0.33) in the LASSO cohort using an adjusted logistic regression model. Meta-analysis provided evidence of a significant association of rs2231142 with allopurinol response (OR = 2.43, P = 6.2 × 10-7), but not rs10011796 (OR = 1.06, P = 0.69). Conclusion This study has confirmed the significant association of ABCG2 rs2231142 with poor response to allopurinol.

Association of Crohn’s disease-related chromosome 1q32 with ankylosing spondylitis is independent of bowel symptoms and faecal calprotectin

Background Genome-wide association studies have identified a plethora of risk genes for both Crohn’s disease (CD) and ankylosing spondylitis (AS). A subset of genes found to be risk factors for CD have also been found to be risk factors for AS. The objective of our study was to assess whether CD risk genes were associated with non-invasive clinical markers of gut inflammation in patients with AS, indicating a potential subset of patients with clinical as well as genetic overlap. Methods A total of 308 Caucasian patients who fulfilled the modified New York Criteria for AS, were assessed for bowel symptoms using the Dudley Inflammatory Bowel Symptom Questionnaire (DISQ). Of these patients, 157 also had faecal calprotectin measured. All AS patients and 568 healthy controls were genotyped for 10 CD risk loci using predesigned single nucleotide polymorphism (SNP) genotyping assays. Chi-square analysis was used to test for association between genotype and DISQ score and faecal calprotectin level. Results The minor allele of two SNPs, one in chromosome region 1q32 SNP (rs11584383), and one in the gene coding for IL23R (rs11209026) conferred protection against AS. Only the association of 1q32 remained significant after Bonferroni correction for multiple testing. Stratification by DISQ score and faecal calprotectin did not influence the association of 1q32 with AS. Conclusion In patients with AS, the association of the CD 1q32 SNP was independent of non-invasive markers of bowel inflammation. Other CD related SNPs were not found have a significant association with AS.

Nonsynonymous Polymorphism in Guanine Monophosphate Synthetase Is a Risk Factor for Unfavorable Thiopurine Metabolite Ratios in Patients With Inflammatory Bowel Disease

Background Up to 20% of patients with inflammatory bowel disease (IBD) who are refractory to thiopurine therapy preferentially produce 6-methylmercaptopurine (6-MMP) at the expense of 6-thioguanine nucleotides (6-TGN), resulting in a high 6-MMP:6-TGN ratio (>20). The objective of this study was to evaluate whether genetic variability in guanine monophosphate synthetase (GMPS) contributes to preferential 6-MMP metabolizer phenotype. Methods Exome sequencing was performed in a cohort of IBD patients with 6-MMP:6-TGN ratios of >100 to identify nonsynonymous single nucleotide polymorphisms (nsSNPs). In vitro assays were performed to measure GMPS activity associated with these nsSNPs. Frequency of the nsSNPs was measured in a cohort of 530 Caucasian IBD patients. Results Two nsSNPs in GMPS (rs747629729, rs61750370) were detected in 11 patients with very high 6-MMP:6-TGN ratios. The 2 nsSNPs were predicted to be damaging by in silico analysis. In vitro assays demonstrated that both nsSNPs resulted in a significant reduction in GMPS activity (P < 0.05). The SNP rs61750370 was significantly associated with 6-MMP:6-TGN ratios ≥100 (odds ratio, 5.64; 95% confidence interval, 1.01-25.12; P < 0.031) in a subset of 264 Caucasian IBD patients. Conclusions The GMPS SNP rs61750370 may be a reliable risk factor for extreme 6MMP preferential metabolism.

THU0366 Association of Chromosome 1Q32 with Ankylosing Spondylitis Is Independent of Bowel Symptoms and Faecal Calprotectin

Background Colonoscopic, endoscopic, and histological studies have demonstrated that intestinal inflammation, similar to the ileo-colitis seen in Crohns disease (CD), is a common feature of ankylosing spondylitis (AS). More recently, the existence of a shared genetic basis to CD and AS has been demonstrated [1,2]. Objectives To test whether the association of known CD risk loci with AS is primarily due to the presence of bowel inflammation in AS patients. Methods 286 Caucasian patients fulfilling the modified New York criteria for AS and with no history of inflammatory bowel disease were assessed non-invasively for bowel inflammation using faecal calprotectin and the Dudley Inflammatory Bowel Symptom Questionnaire (DISQ) [3]. All patients and 568 matched healthy controls were genotyped with TaqMan® SNP genotyping assays for the confirmed CD risk loci [2], 1q32 (rs11584383),JAK2 (rs10758669), CDKAL1 (rs6908425), IL12B (rs100454310), ZPBP2 (rs2872507), MUC19/LRRK2 (rs11175593), STAT3 (rs744166), and IL23R (rs1343151, rs10489630, rs11209026). Chi square testing was used to test for association. Results Minor alleles of 1q32 SNP rs11584383 (p=0.002, OR=0.69, 95% CI 0.55–0.87), and IL23R SNPs rs11209026 (p=0.011, OR=0.53, 95% CI 0.32–0.87) and rs1343151 (p=0.027, OR=0.77, 95% CI 0.61–0.97) all conferred protection against AS. However, only the association of 1q32 SNP rs11584383 remained significant after Bonferroni correction for multiple testing (p=0.02). The Cochrans Q test found no significant difference between ORs after stratification of AS patients by DISQ score and faecal calprotectin (Pdifference >0.09). Conclusions Previously, the association of CD risk loci with susceptibility to AS has been attributed to the co-occurrence of asymptomatic intestinal inflammation which is well recognised and supports the concept that CD and AS are two extremes of a related genetic and phenotypic disease spectrum. However, our study provides preliminary evidence that the association of the confirmed CD risk locus 1q32 SNP rs11584383 with AS is independent of bowel inflammation. References Parkes M, et al. 2013. Nature reviews Genetics. 14(9):661–673. Danoy P et al. 2010. PLoS genetics. 6(12):e1001195. Stebbings S et al. 2012. Rheumatology. 51(5):858–865. Disclosure of Interest None declared