B. P. Wordsworth

Interaction between ERAP1 and HLA-B27 in ankylosing spondylitis implicates peptide handling in the mechanism for HLA-B27 in disease susceptibility

Ankylosing spondylitis is a common form of inflammatory arthritis predominantly affecting the spine and pelvis that occurs in approximately 5 out of 1,000 adults of European descent. Here we report the identification of three variants in the RUNX3, LTBR-TNFRSF1A and IL12B regions convincingly associated with ankylosing spondylitis (P < 5 × 10−8 in the combined discovery and replication datasets) and a further four loci at PTGER4, TBKBP1, ANTXR2 and CARD9 that show strong association across all our datasets (P < 5 × 10−6 overall, with support in each of the three datasets studied). We also show that polymorphisms of ERAP1, which encodes an endoplasmic reticulum aminopeptidase involved in peptide trimming before HLA class I presentation, only affect ankylosing spondylitis risk in HLA-B27–positive individuals. These findings provide strong evidence that HLA-B27 operates in ankylosing spondylitis through a mechanism involving aberrant processing of antigenic peptides.

HLA class I associations of ankylosing spondylitis in the white population in the United Kingdom.

OBJECTIVE: To investigate the HLA class I associations of ankylosing spondylitis (AS) in the white population, with particular reference to HLA-B27 subtypes. METHODS: HLA-B27 and -B60 typing was performed in 284 white patients with AS. Allele frequencies of HLA-B27 and HLA-B60 from 5926 white bone marrow donors were used for comparison. HLA-B27 subtyping was performed by single strand conformation polymorphism (SSCP) in all HLA-B27 positive AS patients, and 154 HLA-B27 positive ethnically matched blood donors. RESULTS: The strong association of HLA-B27 and AS was confirmed (odds ratio (OR) 171, 95% confidence interval (CI) 135 to 218; p < 10(-99)). The association of HLA-B60 with AS was confirmed in HLA-B27 positive cases (OR 3.6, 95% CI 2.1 to 6.3; p < 5 x 10(-5)), and a similar association was demonstrated in HLA-B27 negative AS (OR 3.5, 95% CI 1.1 to 11.4; p < 0.05). No significant difference was observed in the frequencies of HLA-B27 allelic subtypes in patients and controls (HLA-B*2702, three of 172 patients v five of 154 controls; HLA-B*2705, 169 of 172 patients v 147 of 154 controls; HLA-B*2708, none of 172 patients v two of 154 controls), and no novel HLA-B27 alleles were detected. CONCLUSION: HLA-B27 and -B60 are associated with susceptibility to AS, but differences in HLA-B27 subtype do not affect susceptibility to AS in this white population.

Ankylosing spondylitis in West Africans—evidence for a non-HLA-B27 protective effect

OBJECTIVE To determine the prevalence of ankylosing spondylitis in the Fula ethnic group in The Gambia, and relate the disease prevalence to the B27 frequency and subtype distribution of that population. METHODS 215 first degree relatives of 48 B27 positive Fula twin pairs, and 900 adult Fula males were screened for ankylosing spondylitis by clinical and, where appropriate, radiographic means. The B27 prevalence was determined by PCR/sequence specific oligonucleotides on finger prick samples from 100 unrelated Fula, and B27 subtype distribution by SSCP on unrelated B27 positive individuals. This data were then compared with the prevalence of ankylosing spondylitis among B27 positive Caucasians. RESULTS No case of ankylosing spondylitis was seen. Six per cent of Fula are B27 positive, of which 32% are B*2703 and 68% B*2705. Assuming the penetrance of ankylosing spondylitis in B27 positive Fula is the same as in B27 positive Caucasians, the probability of not observing any cases of ankylosing spondylitis among the Fula examined is remote (P = 6.7 × 10-6). Similarly, the chance of not seeing any cases among those expected to be either B*2705 or B*2703 was small (P = 3.2 × 10-4 for B*2705, and P = 0.02 for B*2703). CONCLUSIONS The risk of developing ankylosing spondylitis in B27 positive Fula is lower than in B27 positive Caucasians. This is not explained by the B27 subtype distribution among Fula, and suggests the presence of some non-B27 protective factor reducing the prevalence of ankylosing spondylitis in this population.

Genetic susceptibility to ankylosing spondylitis

Ankylosing spondylitis is a highly heritable, common rheumatic condition, primarily affecting the axial skeleton. The association with HLA-B27 has been demonstrated worldwide, and evidence for a role of HLA-B27 in disease comes from linkage and association studies in humans, and transgenic animal models. However, twin studies indicate that HLA-B27 contributes only 16% of the total genetic risk for disease. Furthermore, there is compelling evidence that non-B27 genes, both within and outwith the major histocompatability complex, are involved in disease aetiology. In this post-genomic era we have the tools to help elicit the genetic basis of disease. This review describes methods for genetic investigation of ankylosing spondylitis, and summarises the status of current research in this exciting area.

Elucidating the chromosome 9 association with AS; CARD9 is a candidate gene

Ankylosing spondylitis (AS) is polygenic with contributions from the immunologically relevant genes HLA-B*27, ERAP1 and IL23R. A recent genome-wide association screen (GWAS) identified associations (P∼0.005) with the non-synonymous single-nucleotide polymorphisms (nsSNPs), rs4077515 and rs3812571, in caspase recruitment domain-containing protein 9 (CARD9) and small nuclear RNA-activating complex polypeptide 4 (SNAPC4) on chromosome 9q that had previously been linked to AS. We replicated these associations in a study of 730 AS patients compared with 2879 historic disease controls (rs4077515 P=0.0004, odds ratio (OR)=1.2, 95% confidence interval (CI)=1.1–1.4; rs3812571 P=0.0003, OR=1.2, 95% CI=1.1–1.4). Meta-analysis revealed strong associations of both SNPs with AS, rs4077515 P=0.000005, OR=1.2, 95% CI=1.1–1.3 and rs3812571 P=0.000006, OR=1.2, 95% CI=1.1–1.3. We then typed 1604 AS cases and 1020 controls for 13 tagging SNPs; 6 showed at least nominal association, 5 of which were in CARD9. We imputed genotypes for 13 additional SNPs but none was more strongly associated with AS than the tagging SNPs. Finally, interrogation of an mRNA expression database revealed that the SNPs most strongly associated with AS (or in strong linkage disequilibrium) were those most associated with CARD9 expression. CARD9 is a plausible candidate for AS given its central role in the innate immune response.

Analysis of the MHC class II encoded components of the HLA class I antigen processing pathway in ankylosing spondylitis.

OBJECTIVES--The evaluation of the role of polymorphism within the class II encoded antigen processing genes, LMP2 and TAP, in susceptibility to ankylosing spondylitis (AS). METHODS--Eighty five patients with ankylosing spondylitis, 35 B27 positive healthy controls, and 55 unrelated healthy controls were studied. TAP1 and TAP2 alleles were assigned by ARMS PCR, and LMP2 alleles were assigned by restriction enzyme digestion of a PCR product. RESULTS--The TAP1C allele was increased in the AS group (6%) compared with random controls (1%), p = 0.03 and TAP2E was increased in AS (3.5%) compared with random controls (0%), p = 0.05. However, the frequencies of these alleles were also increased in B27 matched controls. There were no differences in LMP2 allele or genotype frequencies between AS and either of the control groups. Partitioning of patients according to presence or absence of uveitis did not reveal any significant associations. CONCLUSIONS--Increases of the minor TAP alleles, 1C and 2E, in AS reflect linkage disequilibrium between these alleles and HLA-B27. Polymorphism of the class I antigen processing pathway does not contribute significantly to AS susceptibility nor to the development of anterior uveitis associated with AS.

MacIntosh arthroplasty for the rheumatoid knee: a 10-year follow up.

The results of 75 MacIntosh arthroplasties performed for rheumatoid arthritis of the knee in 63 patients were reviewed at least 10 years after surgery. Forty-two knees in 35 patients were available for assessment. Eleven arthroplasties had been revised to total knee replacement without difficulty because of pain or poor function. The remaining 31 knees in 25 patients gave good or excellent results in 22 cases, fair in eight, and poor in one. Seven patients could not be traced, and 21 patients representing 26 knees had died. At least half these knees had given satisfactory results immediately before death judged by review of the case notes. The difficulty of comparing functional status with the preoperative state because of progressive multiarticular disease was highlighted. Although greater angular deformities preoperatively reduced the chance of success in the medium term, late failure of the arthroplasty after five years was very rare. Approximately two-thirds of all the arthroplasties performed gave satisfactory results at 10-year follow up or until the time of death.

Interleukin 10 polymorphisms in ankylosing spondylitis

Genetic polymorphisms of the IL10 promoter region have been implicated in many autoimmune diseases, including seronegative spondyloarthropathies. We studied three SNPs (IL10–1087, −824, and −597) and two microsatellites (IL10R and IL10G) lying within the promoter region of IL10 for association with susceptibility to and clinical manifestations of ankylosing spondylitis (AS), a common form of spondyloarthritis. Four hundred and sixty-eight individuals from 182 Finnish families affected with AS were studied. No association between individual IL10 promoter region polymorphisms or marker haplotype was observed with susceptibility to AS, but weak association was noted between the IL10–597 and −824 SNPs and age of disease onset (P=0.01 for each SNP). The IL10.G4 allele was associated with BASFI (corrected for disease duration) (P=0.03). We conclude that IL10 promoter polymorphisms have no significant effect on susceptibility to AS, but may play a minor role in determining age of disease onset and disease severity.

The histone demethylase JARID1A is associated with susceptibility to ankylosing spondylitis.

Associations with disease identified by genome-wide association studies (GWAS) must be replicated and refined to validate causative variants. In the Wellcome Trust Case Control Consortium (WTCCC) GWAS using 14 500 non-synonymous single nucleotide polymorphisms (nsSNP), rs11062385 (a nsSNP in JARID1A) showed nominal association with ankylosing spondylitis (AS) (P=0.0006, odds ratio (OR)=1.26, 95% confidence interval (95% CI)=1.1–1.4). To replicate and refine the association of JARID1A, rs11062385 was genotyped in 730 further cases and compared with allele frequencies in non-AS disease cohorts typed by WTCCC. We replicated the initial association (P=0.04, OR=1.16, 95% CI=1.01–1.34) and identified a strengthened association with AS in a meta-analysis of this new study combined with the original WTCCC study (P=0.0001, OR=1.21, 95% CI=1.10–1.33). We also genotyped nine further intronic tagging SNPs in JARID1A in 1604 AS cases and 1020 new control samples, but none was associated with AS. JARID1A or a locus in strong linkage disequilibrium with it is a positional candidate for susceptibility to AS.

Lethal osteogenesis imperfecta and a collagen gene deletion. Length polymorphism provides an alternative explanation

SummaryA 300 base pair deletion near the 3′-end of the gene encoding Type II (cartilage) collagen has been implicated in the pathogenesis of perinatal lethal osteogenesis imperfecta. We have found similar deletions occurring at a high frequency in normal Asian Indian and West Indian populations generated by a length polymorphism just beyond the 3′-end of the gene. We suggest that this polymorphism provides an alternative explanation of the original results.