*Article* **HLA Allele Prevalence in Disease-Modifying Antirheumatic Drugs-Responsive Enthesitis and/or Arthritis Not Fulfilling ASAS Criteria: Comparison with Psoriatic and Undifferentiated Spondyloarthritis**

**Elvira Favoino, Livio Urso, Alessandra Serafino, Francesca Misceo, Giacomo Catacchio, Marcella Prete and Federico Perosa \***

> Department of Biomedical Science and Human Oncology (DIMO), Rheumatic and Systemic Autoimmune Diseases Unit, University of Bari Medical School, Piazza G. Cesare 11, I-70124 Bari, Italy; elvira.favoino@uniba.it (E.F.); livio.urso@gmail.com (L.U.); aleserafik@gmail.co (A.S.); franc.misceo@gmail.com (F.M.); giaco.catacchio@gmail.com (G.C.); marcella.prete@uniba.it (M.P.) **\*** Correspondence: federico.perosa@uniba.it; Tel.: +39-80-547-88-91; Fax: +39-80-547-88-20

**Citation:** Favoino, E.; Urso, L.; Serafino, A.; Misceo, F.; Catacchio, G.; Prete, M.; Perosa, F. HLA Allele Prevalence in Disease-Modifying Antirheumatic Drugs-Responsive Enthesitis and/or Arthritis Not Fulfilling ASAS Criteria: Comparison with Psoriatic and Undifferentiated Spondyloarthritis. *J. Clin. Med.* **2021**, *10*, 3006. https://doi.org/ 10.3390/jcm10143006

Academic Editor: Eugen Feist

Received: 28 May 2021 Accepted: 3 July 2021 Published: 6 July 2021

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**Abstract:** Spondyloarthritis (SpA) is a group of inflammatory rheumatic diseases characterized by common clinical features, such as inflammatory enthesitis, arthritis and/or back pain. SpA is strongly associated with human leukocyte antigen (HLA) class I allotype B27. Ankylosing spondylitis has historically been the SpA subgroup with one of the strongest, best-proven associations with HLA-B27. The remaining SpA subgroups, namely psoriatic arthritis (PsA), inflammatory bowel diseases-associated arthritis/spondylitis, reactive arthritis, and undifferentiated SpA (uSpA), have also been associated with HLA allotypes other than HLA-B27. In this retrospective study, we analyzed the association between the HLA class I and II haplotypes and the susceptibility to enthesitis and/or arthritis (E/A). Special attention was paid to E/A responding to disease-modifying antirheumatic drugs (DMARDs) not fulfilling ASAS classification criteria (ASAS−), as compared to ASAS<sup>+</sup> forms including PsA and uSpA. The whole E/A group showed significant independent associations with HLA-A28(68), B27, Cw3, Cw12, and DQ1; taken singly, PsA was associated with HLA-B27 and DQ1, uSpA with HLA-B16(38,39) and B27, and E/A ASAS− with HLA-A28(68), Cw8, and Cw12. This study identified novel risk HLA allotypes for different SpA subgroups in an Italian population. HLA typing could aid the diagnosis and treatment of E/A subgroups, including DMARDS-responsive forms not fulfilling ASAS classification criteria.

**Keywords:** spondyloarthritis; human leukocyte antigen; undifferentiated enthesitis and/or arthritis; ASAS classification criteria; clinical management
