OBJECTIVE: HLA association fine-mapping studies have shown the effects of missense variants in HLA-DRB1 on rheumatoid arthritis (RA) susceptibility, prognosis, and autoantibody production. However, the phenotypic effects of expression changes in HLA-DRB1 remain poorly understood. Therefore, we investigated the allele-specific expression of HLA-DRB1 and its effect on an HLA-DRβ1 structure-associated trait in RA. METHODS: We quantified the allele-specific expression of each HLA-DRB1 3-field classic allele in 48 Korean RA patients with anti-citrullinated protein antibodies (ACPAs) and 319 healthy European subjects by using both RNA sequencing and HLA-DRB1 genotype data to calculate the relative expression strength of multiple HLA-DRB1 alleles (n = 14 in Koreans and n = 25 in Europeans) in each population. The known association between ACPA level and alanine at position 74 of HLA-DRβ1 in ACPA-positive RA was revisited to understand the phenotypic effect of allele-specific expression of HLA-DRB1 by modeling multivariate logistic regression with the genomic dosage or relative expression dosage of Ala-74 in 2 independent sets of 1,723 Korean RA patients with ACPA. RESULTS: The relative expression strength was highly allele-specific, causing imbalanced allelic expression in HLA-DRB1 heterozygotes. The association between HLA-DRβ1 Ala-74 and ACPA level in RA was better explained by relative expression dosage of Ala-74 than by the genomic dosage (change in Akaike's information criterion = -6.98). Moreover, the expression variance of Ala-74 in Ala-74 heterozygotes with no genomic variance of Ala-74 was significantly associated with ACPA level (P = 2.26 × 10-3 ). CONCLUSION: Our findings illustrate the advantage of integrating quantitative and qualitative changes in HLA-DRB1 into a single model for understanding HLA-DRB1 associations.
OBJECTIVE:HLA association fine-mapping studies have shown the effects of missense variants in HLA-DRB1 on rheumatoid arthritis (RA) susceptibility, prognosis, and autoantibody production. However, the phenotypic effects of expression changes in HLA-DRB1 remain poorly understood. Therefore, we investigated the allele-specific expression of HLA-DRB1 and its effect on an HLA-DRβ1 structure-associated trait in RA. METHODS: We quantified the allele-specific expression of each HLA-DRB1 3-field classic allele in 48 Korean RApatients with anti-citrullinated protein antibodies (ACPAs) and 319 healthy European subjects by using both RNA sequencing and HLA-DRB1 genotype data to calculate the relative expression strength of multiple HLA-DRB1 alleles (n = 14 in Koreans and n = 25 in Europeans) in each population. The known association between ACPA level and alanine at position 74 of HLA-DRβ1 in ACPA-positive RA was revisited to understand the phenotypic effect of allele-specific expression of HLA-DRB1 by modeling multivariate logistic regression with the genomic dosage or relative expression dosage of Ala-74 in 2 independent sets of 1,723 Korean RApatients with ACPA. RESULTS: The relative expression strength was highly allele-specific, causing imbalanced allelic expression in HLA-DRB1 heterozygotes. The association between HLA-DRβ1 Ala-74 and ACPA level in RA was better explained by relative expression dosage of Ala-74 than by the genomic dosage (change in Akaike's information criterion = -6.98). Moreover, the expression variance of Ala-74 in Ala-74 heterozygotes with no genomic variance of Ala-74 was significantly associated with ACPA level (P = 2.26 × 10-3 ). CONCLUSION: Our findings illustrate the advantage of integrating quantitative and qualitative changes in HLA-DRB1 into a single model for understanding HLA-DRB1 associations.
Authors: Miranda Houtman; Espen Hesselberg; Lars Rönnblom; Lars Klareskog; Vivianne Malmström; Leonid Padyukov Journal: Front Immunol Date: 2021-08-17 Impact factor: 7.561