[X-linked hypophosphatemia caused by a novel variant in the PHEX gene]

X-linked hypophosphatemia (XLH) (OMIM #307800) is a rare, chronic, and progressive genetic musculoskeletal disorder caused by loss-of-function variants in the PHEX gene located at locus Xp22.11. Clinical manifestations of XLH include short stature, dental abnormalities, and lower limb deformities, although the phenotype is variable. Diagnosis is clinical, biochemical, and radiological, but genetic testing is also recommended. This case report describes a 29-year-old female patient with no family history related to her disease, presenting with short stature, dental abnormalities, lower limb deformities, elevated levels of serum fibroblast growth factor-23 (171 pg/mL), hypophosphatemia (1.9 mg/dL), and decreased renal tubular phosphorus reabsorption (78%). The radiological examination showed bilateral genu valgum and bowing of lower limbs. The molecular testing revealed the pathogenic variant ChrX:22.047.048 A>G (c.188-2A>G) in heterozygosis, localized in the PHEX gene and not previously described in the literature. The identification of new PHEX variants could help to improve patient diagnosis and outcomes as well as to establish a phenotype-genotype correlation in XLH.