(403) The Importance of Using High Resolution HLA Typing Of HLA-B*27 In Determining Disease Association with Ankylosing Spondylitis

Aim: Possession of HLA-B*27 has a strong association with inflammatory rheumatic diseases, most commonly ankylosing spondylitis (AS). Clinicians routinely request B*27 typing to support the diagnosis and treatment of AS and laboratory results are reported as positive or negative. However, more than 400 B*27 alleles have been named and some of the Common and Well-documented (CWD) alleles are not associated with AS. This investigation highlights the importance of reporting the high resolution typing of B*27 in determining disease association with AS.

Methods: HLA typing was performed for individuals who had HLA typing orders for solid organ transplant, blood or bone marrow transplant, and disease association. High resolution HLA Typing was performed by Next Generation Sequencing (NGS) using the CareDX Alloseq TX 17.1 library preparation kit. DNA isolations were performed from whole blood (collected in ACD or EDTA), buccal swab, and various other specimen types using the Maxwell 16 instrument or the Qiagen Qiamp DNA Blood Mini Kit. The prepared libraries were loaded onto the Illumina MiSeq genetic analyzer. HLA typing data was analyzed with CareDX AlloSeq Assign software using IPD-IMGT/HLA 3.45.1 to 3.57.0 from March 2022 to April 22, 2025.

Results: A total of 2138 samples were tested, and 123 (5.8%) of those samples had at least one B*27 allele. Six different B*27 alleles were observed in this patient population: B*27:02 (n=18); B*27:03 (n=3); B*27:04 (n=8); B*27:05 (n=83); B*27:06 (n=3); B*27:07 (n=8) (Figure 1). Of the 2138 total samples tested, 389 were HLA-B*27 orders. Of these, 41 (10.5%) samples had at least one B*27 allele. Five different B*27 alleles were observed: B*27:02 (n=3); B*27:03 (n=1); B*27:04 (n=6); B*27:05 (n=30); B*27:07 (n=1) (Figure 2).

Conclusion: In this investigation, six B*27 alleles were detected with each having a variable association with AS. B*27:06 was detected which is one of two alleles which have not been found to have a strong association to AS. B*27:03 which has an inconclusive association with AS was also detected. Ethnicity influences B*27 allele frequencies and association with AS. Rare B*27 alleles can also be detected by NGS and their association with AS is unknown or inconclusive. When reporting rare alleles, it might be helpful to include comments to ensure that clinicians are aware of the allelic differences for B*27 and AS.