McCrystal Dahir, KathrynBlack, MargoGottesman, Gary S.Imel, Erik A.Mumm, StevenNichols, Cindy M.Whyte, Michael P.2024-05-082024-05-082022-12-01Dahir, K. M., Black, M., Gottesman, G. S., Imel, E. A., Mumm, S., Nichols, C. M., & Whyte, M. P. (2022). X‐Linked Hypophosphatemia Caused by the Prevailing North American PHEX Variant c.*231A>G; Exon 13–15 Duplication Is Often Misdiagnosed as Ankylosing Spondylitis and Manifests in Both Men and Women. JBMR Plus, 6(12), e10692. https://doi.org/10.1002/jbm4.10692https://hdl.handle.net/1805/40561Inactivating mutations of the gene coding for phosphate‐regulating endopeptidase homolog X‐linked (PHEX) cause X‐linked hypophosphatemia (XLH). A novel PHEX variant, c.*231A>G; exon 13–15 duplication, has emerged as a common cause of XLH in North America, emphasizing the importance of delineating its clinical presentation. Here, a comprehensive description of a five‐generation American kindred of 22 treatment‐naïve individuals harboring the c.*231A>G; exon 13–15 duplication is provided. After XLH was diagnosed in the proposita, pro‐active family members used social media to facilitate a timely assessment of their medical history. Most had normal height and 50% were normophosphatemic. Thirteen had been given a diagnosis other than XLH, most commonly ankylosing spondylitis, and XLH was only established after genetic testing. The prevalent phenotypic characteristics of c.*231A>G; exon 13–15 duplication were disorders of dentition (68.2%), enthesopathies (54.5%), fractures/bone and joint conditions (50%), lower‐limb deformities (40.9%), hearing loss/tinnitus (40.9%), gait abnormalities (22.7%), kidney stones/nephrocalcinosis (18.2%), chest wall disorders (9.1%), and Chiari/skull malformation (4.5%). More affected males than females, respectively, had gait abnormalities (42.9% versus 13.3%), lower‐limb deformities (71.4% versus 26.7%), and enthesopathies (85.7% versus 40%). Single phenotypes, observed exclusively in females, occurred in 22.7% and multiple phenotypes in 77.3% of the cohort. However, as many as six characteristics could develop in either affected males or females. Our findings will improve diagnostic and monitoring protocols for XLH. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.en-USAttribution-NonCommercial 4.0 Internationalbone disorderscalcium/phosphate metabolismosteomalaciaricketsArticle