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Rheumatic heart disease follows Group A Streptococcus (GAS) infection in Aboriginal Australians. A genome-wide study identified HLA as the strongest genetic risk factor. Risk and protective HLA_DQA1_DQB1 haplotypes bound with different affinities to core epitopes of pathogenic GAS M proteins. Abstract Background Rheumatic heart disease (RHD) after group A streptococcus (GAS) infections is heritable and prevalent in Indigenous populations. Molecular mimicry between human and GAS proteins triggers proinflammatory cardiac valve-reactive T cells. Methods Genome-wide genetic analysis was undertaken in 1263 Aboriginal Australians (398 RHD cases; 865 controls). Single-nucleotide polymorphisms were genotyped using Illumina HumanCoreExome BeadChips. Direct typing and imputation was used to fine-map the human leukocyte antigen (HLA) region. Epitope binding affinities were mapped for human cross-reactive GAS proteins, including M5 and M6. Results The strongest genetic association was intronic to HLA-DQA1 (rs9272622; P = 1.86 × 10−7). Conditional analyses showed rs9272622 and/or DQA1*AA16 account for the HLA signal. HLA-DQA1*0101_DQB1*0503 (odds ratio [OR], 1.44; 95% confidence interval [CI], 1.09–1.90; P = 9.56 × 10−3) and HLA-DQA1*0103_DQB1*0601 (OR, 1.27; 95% CI, 1.07–1.52; P = 7.15 × 10−3) were risk haplotypes; HLA_DQA1*0301-DQB1*0402 (OR 0.30, 95%CI 0.14–0.65, P = 2.36 × 10−3) was protective. Human myosin cross-reactive N-terminal and B repeat epitopes of GAS M5/M6 bind with higher affinity to DQA1/DQB1 alpha/beta dimers for the 2-risk haplotypes than the protective haplotype. Conclusions Variation at HLA_DQA1-DQB1 is the major genetic risk factor for RHD in Aboriginal Australians studied here. Cross-reactive epitopes bind with higher affinity to alpha/beta dimers formed by risk haplotypes, supporting molecular mimicry as the key mechanism of RHD pathogenesis.

Graham Heap, Tariq Ahmad and colleagues show that common variants in the HLA-DQA1–HLA-DRB1 region confer susceptibility to thiopurine-induced pancreatitis in individuals undergoing treatment for inflammatory bowel diseases. These findings could help identify patients at risk of developing this serious adverse reaction to thiopurine therapy. Pancreatitis occurs in approximately 4% of patients treated with the thiopurines azathioprine or mercaptopurine. Its development is unpredictable and almost always leads to drug withdrawal. We identified patients with inflammatory bowel disease (IBD) who had developed pancreatitis within 3 months of starting these drugs from 168 sites around the world. After detailed case adjudication, we performed a genome-wide association study on 172 cases and 2,035 controls with IBD. We identified strong evidence of association within the class II HLA region, with the most significant association identified at rs2647087 (odds ratio 2.59, 95% confidence interval 2.07–3.26, P = 2 × 10 −16 ). We replicated these findings in an independent set of 78 cases and 472 controls with IBD matched for drug exposure. Fine mapping of the HLA region identified association with the HLA-DQA1*02:01–HLA-DRB1*07:01 haplotype. Patients heterozygous at rs2647087 have a 9% risk of developing pancreatitis after administration of a thiopurine, whereas homozygotes have a 17% risk.

Soumya Raychaudhuri and colleagues present a detailed analysis of the association between the HLA region and type 1 diabetes risk. They find that variants at three amino acid positions in HLA-DQβ1 and HLA-DRβ1 account for a large fraction of the association signal, acting through a combination of additive and interaction effects. Variation in the human leukocyte antigen (HLA) genes accounts for one-half of the genetic risk in type 1 diabetes (T1D). Amino acid changes in the HLA-DR and HLA-DQ molecules mediate most of the risk, but extensive linkage disequilibrium complicates the localization of independent effects. Using 18,832 case-control samples, we localized the signal to 3 amino acid positions in HLA-DQ and HLA-DR. HLA-DQβ1 position 57 (previously known; P = 1 × 10 −1,355 ) by itself explained 15.2% of the total phenotypic variance. Independent effects at HLA-DRβ1 positions 13 ( P = 1 × 10 −721 ) and 71 ( P = 1 × 10 −95 ) increased the proportion of variance explained to 26.9%. The three positions together explained 90% of the phenotypic variance in the HLA-DRB1 – HLA-DQA1 – HLA-DQB1 locus. Additionally, we observed significant interactions for 11 of 21 pairs of common HLA-DRB1 – HLA-DQA1 – HLA-DQB1 haplotypes ( P = 1.6 × 10 −64 ). HLA-DRβ1 positions 13 and 71 implicate the P4 pocket in the antigen-binding groove, thus pointing to another critical protein structure for T1D risk, in addition to the HLA-DQ P9 pocket.

Low muscle strength is an important heritable indicator of poor health linked to morbidity and mortality in older people. In a genome-wide association study meta-analysis of 256,523 Europeans aged 60 years and over from 22 cohorts we identify 15 loci associated with muscle weakness (European Working Group on Sarcopenia in Older People definition: n  = 48,596 cases, 18.9% of total), including 12 loci not implicated in previous analyses of continuous measures of grip strength. Loci include genes reportedly involved in autoimmune disease ( HLA-DQA1 p  = 4 × 10 −17 ), arthritis ( GDF5 p  = 4 × 10 −13 ), cell cycle control and cancer protection, regulation of transcription, and others involved in the development and maintenance of the musculoskeletal system. Using Mendelian randomization we report possible overlapping causal pathways, including diabetes susceptibility, haematological parameters, and the immune system. We conclude that muscle weakness in older adults has distinct mechanisms from continuous strength, including several pathways considered to be hallmarks of ageing. Muscle weakness has been associated with morbidity and mortality in older people. Here, the authors have investigated this trait further by performing a genome-wide meta-analysis of grip strength and Mendelian randomization to discover causal relationships between muscle weakness and other diseases.

Rosacea is a common, chronic skin disease that is currently incurable. Although environmental factors influence rosacea, the genetic basis of rosacea is not established. In this genome-wide association study, a discovery group of 22,952 individuals (2,618 rosacea cases and 20,334 controls) was analyzed, leading to identification of two significant single-nucleotide polymorphisms (SNPs) associated with rosacea, one of which replicated in a new group of 29,481 individuals (3,205 rosacea cases and 26,262 controls). The confirmed SNP, rs763035 (P=8.0 × 10−11 discovery group; P=0.00031 replication group), is intergenic between HLA-DRA and BTNL2. Exploratory immunohistochemical analysis of HLA-DRA and BTNL2 expression in papulopustular rosacea lesions from six individuals, including one with the rs763035 variant, revealed staining in the perifollicular inflammatory infiltrate of rosacea for both proteins. In addition, three HLA alleles, all MHC class II proteins, were significantly associated with rosacea in the discovery group and confirmed in the replication group: HLA-DRB1*03:01 (P=1.0 × 10−8 discovery group; P=4.4 × 10−6 replication group), HLA-DQB1*02:01 (P=1.3 × 10−8 discovery group; P=7.2 × 10−6 replication group), and HLA-DQA1*05:01 (P=1.4 × 10−8 discovery group; P=7.6 × 10−6 replication group). Collectively, the gene variants identified in this study support the concept of a genetic component for rosacea, and provide candidate targets for future studies to better understand and treat rosacea.

Ingileif Jonsdottir, Kari Stefansson and colleagues show that variants in the HLA class II region contribute to tuberculosis risk in populations of European ancestry. They propose that the associated variants influence disease risk by altering expression of HLA class II molecules presenting protective M. tuberculosis antigens to T cells. Mycobacterium tuberculosis infections cause 9 million new tuberculosis cases and 1.5 million deaths annually 1 . To identify variants conferring risk of tuberculosis, we tested 28.3 million variants identified through whole-genome sequencing of 2,636 Icelanders for association with tuberculosis (8,162 cases and 277,643 controls), pulmonary tuberculosis (PTB) and M. tuberculosis infection. We found association of three variants in the region harboring genes encoding the class II human leukocyte antigens (HLAs): rs557011[T] (minor allele frequency (MAF) = 40.2%), associated with M. tuberculosis infection (odds ratio (OR) = 1.14, P = 3.1 × 10 −13 ) and PTB (OR = 1.25, P = 5.8 × 10 −12 ), and rs9271378[G] (MAF = 32.5%), associated with PTB (OR = 0.78, P = 2.5 × 10 −12 )—both located between HLA - DQA1 and HLA - DRB1 —and a missense variant encoding p.Ala210Thr in HLA - DQA1 (MAF = 19.1%, rs9272785), associated with M . tuberculosis infection ( P = 9.3 × 10 −9 , OR = 1.14). We replicated association of these variants with PTB in samples of European ancestry from Russia and Croatia ( P < 5.9 × 10 −4 ). These findings show that the HLA class II region contributes to genetic risk of tuberculosis, possibly through reduced presentation of protective M . tuberculosis antigens to T cells.

Rheumatic heart disease (RHD) is a complication of group A streptococcal infection that results from a complex interaction between the genetic make-up of the host, the infection itself and several other environmental factors, largely reflecting poverty. RHD is estimated to affect 33.4 million people and results in 10.5 million disability-adjusted life-years lost globally. The disease has long been considered heritable but still little is known about the host genetic factors that increase or reduce the risk of developing RHD. In the 1980s and 1990s, several reports linked the disease to the human leukocyte antigen (HLA) locus on chromosome 6, followed in the 2000s by reports implicating additional candidate regions elsewhere in the genome. Subsequently, the search for susceptibility loci has been reinvigorated by the use of genome-wide association studies (GWAS) through which millions of variants can be tested for association in thousands of individuals. Early findings implicate not only HLA, particularly the HLA-DQA1 to HLA-DQB1 region, but also the immunoglobulin heavy chain locus, including the IGHV4-61 gene segment, on chromosome 14. In this Review, we assess the emerging role of GWAS in assessing RHD, outlining both the advantages and disadvantages of this approach. We also highlight the potential use of large-scale, publicly available data and the value of international collaboration to facilitate comprehensive studies that produce findings that have implications for clinical practice.Rheumatic heart disease is a complication of group A streptococcal infection and rheumatic fever. In this Review, Muhamed and colleagues assess the emerging role of genome-wide association studies in detecting loci associated with genetic susceptibility to rheumatic heart disease.

Aims/hypothesis The aim of this work was to explore molecular amino acids (AAs) and related structures of HLA-DQA1-DQB1 that underlie its contribution to the progression from stages 1 or 2 to stage 3 type 1 diabetes. Methods Using high-resolution DQA1 and DQB1 genotypes from 1216 participants in the Diabetes Prevention Trial-Type 1 and the Diabetes Prevention Trial, we applied hierarchically organised haplotype association analysis (HOH) to decipher which AAs contributed to the associations of DQ with disease and their structural properties. HOH relied on the Cox regression to quantify the association of DQ with time-to-onset of type 1 diabetes. Results By numerating all possible DQ heterodimers of α- and β-chains, we showed that the heterodimerisation increases genetic diversity at the cellular level from 43 empirically observed haplotypes to 186 possible heterodimers. Heterodimerisation turned several neutral haplotypes ( DQ2.2 , DQ2.3 and DQ4.4 ) to risk haplotypes ( DQ2.2/2.3-DQ4.4 and DQ4.4-DQ2.2 ). HOH uncovered eight AAs on the α-chain (−16α, −13α, −6α, α22, α23, α44, α72, α157) and six AAs on the β-chain (−18β, β9, β13, β26, β57, β135) that contributed to the association of DQ with progression of type 1 diabetes. The specific AAs concerned the signal peptide (minus sign, possible linkage to expression levels), pockets 1, 4 and 9 in the antigen-binding groove of the α1β1 domain, and the putative homodimerisation of the αβ heterodimers. Conclusions/interpretation These results unveil the contribution made by DQ to type 1 diabetes progression at individual residues and related protein structures, shedding light on its immunological mechanisms and providing new leads for developing treatment strategies. Data availability Clinical trial data and biospecimen samples are available through the National Institute of Diabetes and Digestive and Kidney Diseases Central Repository portal ( https://repository.niddk.nih.gov/studies ). Graphical Abstract

Antibodies to the phospholipase A2 receptor 1 (PLA2R1) have been reported in 70% of cases of idiopathic membranous nephropathy (IMN). The genetic susceptibility of IMN has been accounted for by HLA DQA1 and PLA2R1 genes. Here we retrospectively quantified PLA2R antibodies by ELISA, and genotyped DQ alleles and PLA2R1 single-nucleotide polymorphisms for association with clinical criteria for disease activity at the time of first sample and with outcome over a median total follow-up of 90 months. In 90 prevalent patients with biopsy-proven IMN, anti-PLA2R antibodies were present in 75% of patients with IMN with active disease and were significantly higher than in patients in partial or complete remission at the time of antibody measurement. There was a differential IgG subclass response (4>2>3>1) at an early stage, i.e., within 6 months of biopsy. Levels of PLA2R antibodies were significantly linked to DQA1*05:01 and DQB1*02:01. Survival analysis of patients with IMN showed that PLA2R antibodies are significantly linked with outcome. Thus, high levels of PLA2R antibodies are linked with active disease and a higher risk of declining renal function during follow-up. Future therapeutic trials in IMN should monitor anti-PLA2R, as patients with a high antibody burden may benefit from earlier therapeutic intervention.

Johannes Schumacher and colleagues report the results of a genetic association study of idiopathic achalasia, a rare motility disorder of the esophagus. They show that common variation in the HLA-DQ region is strongly associated with achalasia risk, implicating immune-mediated processes in this disorder. Idiopathic achalasia is characterized by a failure of the lower esophageal sphincter to relax due to a loss of neurons in the myenteric plexus 1 , 2 . This ultimately leads to massive dilatation and an irreversibly impaired megaesophagus. We performed a genetic association study in 1,068 achalasia cases and 4,242 controls and fine-mapped a strong MHC association signal by imputing classical HLA haplotypes and amino acid polymorphisms. An eight-residue insertion at position 227–234 in the cytoplasmic tail of HLA-DQβ1 (encoded by HLA-DQB1*05:03 and HLA-DQB1*06:01 ) confers the strongest risk for achalasia ( P = 1.73 × 10 −19 ). In addition, two amino acid substitutions in the extracellular domain of HLA-DQα1 at position 41 (lysine encoded by HLA-DQA1*01:03 ; P = 5.60 × 10 −10 ) and of HLA-DQβ1 at position 45 (glutamic acid encoded by HLA-DQB1*03:01 and HLA-DQB1*03:04 ; P = 1.20 × 10 −9 ) independently confer achalasia risk. Our study implies that immune-mediated processes are involved in the pathophysiology of achalasia.