Supplemental Material- JCEM-AMINO ACID POLYMORPHISMS IN HLA CLASS II DIFFERENTIATE BETWEEN THYROID AND POLYGLANDULAR AUTOIMMUNITY

Context: The structure of the human leucocyte antigen (HLA) peptide-binding clefts within the major histocompatibility complex strongly contributes to monoglandular and polyglandular autoimmunity (AP). Objective: To investigate the impact of amino acid polymorphisms on the peptide binding interactions within HLA class II and its association with AP Design: immunogenetic study Setting: Tertiary referral center for autoimmune endocrine diseases Subjects: 587 subjects with AP, autoimmune thyroid disease (AITD), type 1 diabetes (T1D) and healthy controls were typed for HLA class II. Methods: Positions within HLA class II exon 2 where codons translate into different amino acids were detected in all subjects. Amino acids were listed for all codon positions and overall comparisons between disease and control groups with respect to allele distribution at a given locus were performed by assembling rare alleles applying an exact Freeman Halton contingency table test with Monte-Carlo p values based on 150000 samples. Results: The Montecarlo Exact Fisher Test demonstrated marked differences in all three Loci, DQA1, DQB1, DRB1 (p<0.0001) between AP versus both AITD and controls as well as between AP type II (Addison’s disease as major component) and type III (T1D+AITD). Differences were also noted between AP and T1D pertaining to the DRB1 allele (p<0.041). The following seven positions DRB1-13, DRB1-26, DRB1-71, DRB1-74, DQA1-47, DQA1-56, and DQB1-57 significantly contributed to AP Conclusion: Amino acid polymorphisms in codon positions within HLA class II exon 2 confer risk to AP and differentiate between thyroid and polyglandular autoimmunity.