[Attenuated X-linked hypophosphatemia: late diagnosis in an adult patient]

Although patients with X-linked hypophosphatemia (XLH) usually present a phenotype characterized by rickets in children or osteomalacia in adults, short stature, lower limb deformities, and dental abnormalities, this condition can manifest with a wide phenotypic spectrum. In attenuated cases, diagnosis is often delayed, preventing early treatment. We present the case of a 50-year-old woman who was referred to our clinic by her son's pediatrician, who had been diagnosed with XLH through molecular testing. Manifestations suggesting attenuated XLH (mild valgus curvature of the lower limbs, bilateral coxa vara, ligamentous hyperlaxity, and mild hypophosphatemia) were observed. Next-generation sequencing identified the heterozygous variant c.2044_2048delinsATAACTCAG in the PHEX gene. After diagnosis, treatment with phosphorus salts, calcitriol, and cholecalciferol was initiated. This variant has not been previously described and is absent in nearly 1.2 million samples from population banks. The combination of the molecular mechanism with early interruption of protein translation in a coding region, the characteristics of the region where it is located, and the presence of clinical symptoms allow this variant to be classified as pathogenic. Our case illustrates the variability in the XLH phenotype and the importance of genetic testing is crucial in the diagnosis of patients with attenuated manifestations of XLH.