MHC associations of ankylosing spondylitis in East Asians are complex and involve non-HLA-B27 HLA contributions

Abstract

Background The association of HLA-B*27 with AS is amongst the strongest of any known association of a common variant with any human disease. Nonetheless, there is strong evidence indicating that other HLA-B alleles are involved in the disease. Large studies in European case-control cohorts have demonstrated risk associations with HLA-B*40 and multiple other HLA-B, -A and Class II alleles, and demonstrated that in that ethnic group the amino acid sequence at position 97 in HLA-B is the key determinant of HLA associations with AS. A recent study in Korean AS cases and controls additionally identified association at HLA-C*15:02. In the current study we examined the MHC associations of AS in an expanded east Asian cohort. Methods 1,637 Chinese, Taiwanese and Korean AS cases meeting the modified New York Criteria for AS, and 1,589 ethnically matched controls, were genotyped with the Illumina Immunochip, including a dense coverage of the MHC region. HLA genotypes and amino acid composition was imputed using the SNP2HLA program using the Han-MHC reference panel based on the data of Han Chinese subjects (largest Asian MHC reference available (n= 9,689)), and association tested using logistic regression using 10 principal components to control for population stratification effects. Results Strong association was seen with HLA-B*27 (odds ratio (OR) =205.3, P=5.764×10 -244 ). Controlling for this association, the strongest risk association is seen with HLA-C*15 at genome-wide significant level (OR = 7.62, P=9.30×10 -19 ), and confirmed association is also seen with HLA-B*40 at suggestive level (OR= 1.65, P= 2.54x10 -4 ). At amino acid level the strongest association seen in uncontrolled analysis was with histidine at position 114 in HLA-B (p=7.24 x10 -241 ), but conditional analyses suggest that the primary amino acid associations are with lysine at position 70 and asparagine at position 97. Restriction of the ERAP1 association with HLA-B27-positive AS, previously reported in European subjects, was confirmed in East Asians. Conclusions This study confirms in East Asians that the HLA associations of AS are multiple, including previously reported associations at HLA-B*27, -B*40, -C*15 , and –DRB1*01 , as well as novel associations with –DRB1*13 and –B*39 . The HLA-B associations are driven by the amino acids at positions 70 and 97, in the B-pocket of HLA-B.

HLA‐B*27:04 associated with enthesitis and younger age of onset, and HLA‐B allele profile in patients with ankylosing spondylitis in Thailand: A cross‐sectional study

“…Regarding alleles other than HLA‐B*27, a previous study in 1637 east Asian AS patients 5 reported that HLA‐B*40 was associated with AS at a suggestive level (OR: 1.65, P = 2.54 × 10 −4 ) after controlling for HLA‐B*27 . HLA‐B*40 was a quite common allele in both Thai AS and the healthy, 14 and it did not show association with AS.…”

“…Other genes may also associate with AS. Other alleles in major histocompatibility complex (MHC) class I ( HLA‐B*40 and HLA‐C*15 ) are associated with AS, 5 and an allele in non‐MHC (ERAP 1) was reported to be associated with HLA‐B27‐positive AS in both Europeans and East Asians 5 …”

“…4 Other genes may also associate with AS. Other alleles in major histocompatibility complex (MHC) class I (HLA-B*40 and HLA-C*15) are associated with AS, 5 and an allele in non-MHC (ERAP 1) was reported to be associated with HLA-B27positive AS in both Europeans and East Asians. 5 In Thailand, the prevalence of positive HLA-B27 in AS patients was 91%, 6 and the prevalence in healthy populations was estimated to be 4%.…”

“…Other alleles in major histocompatibility complex (MHC) class I (HLA-B*40 and HLA-C*15) are associated with AS, 5 and an allele in non-MHC (ERAP 1) was reported to be associated with HLA-B27positive AS in both Europeans and East Asians. 5 In Thailand, the prevalence of positive HLA-B27 in AS patients was 91%, 6 and the prevalence in healthy populations was estimated to be 4%. 6,7 Lopez-Larrea et al studied 45 Thai AS patients with positive HLA-B27 who were diagnosed as having AS according to the European Spondyloarthropathy Study Group (ESSG), and the HLA-B*27:04, -B*27:05, and -B*27:07 subtypes were identified in those patients.…”