SUN-747 - Functional Physical Performance Tests in Patients of the X-Linked Hypophosphatemia Rickets Program in Argentina

Introduction: X-linked hypophosphatemia (XLH) is a rare inherited disorder characterized by elevated FGF23 levels, chronic hypophosphatemia, impaired bone mineralization, and long-term chronic manifestations. There is limited literature on physical function in XLH patients. In adults, the clinical burden appears to be largely determined by mobility limitations, musculoskeletal pain, and muscle weakness. Muscle involvement and function manifest as progressive weakness, a clinical characteristic resulting from skeletal deformities and compromised by impaired phosphate metabolism.

Objective: To describe values ​​in functional physical performance and muscle strength tests in adult and pediatric XLH patients.
Materials and methods: Descriptive observational study. Patients from the XLH Rickets Program were included in the last two months of 2025. Time, speed, strength, and power variables were described using physical performance tests such as Sit-to-Stand (STS), Timed-to-Go (TUG), Gait Speed, handgrip strength, and maximal voluntary isometric contraction (MCVI) of the quadriceps, as well as the 6-minute walk test (6MWT) in adult and pediatric patients. Categorical variables were expressed as relative frequency percentages, and continuous variables were presented as arithmetic mean, standard deviation, and range, as appropriate.

Results: Twenty-one patients were analyzed: 14 adults over 18 years of age and 7 pediatric patients. Mean age was 26.57 ± 15.18 years, with results separated into adult (A) and pediatric (P) groups: Gait speed A 1.2 ± 0.3 and P 1.4 ± 0.2; TUG A 9.0 ± 1.7, P 6.9 ± 1.1; STS A 11.1 ± 2.4 and P 9.8 ± 1.5; handgrip A 25 ± 7.7, P 12.6 ± 3.9; relative MCVI A 4.7 ± 2.3 and P 5.2 ± 1.7, with lower limb asymmetry A 10 (71%) and P 3 (43%); 6MWT distance A 395 ± 169 and P 492 ± 59, with individuals reaching 80% of the expected distance A 5 (36%) and P 4 (57%).

Conclusion: We obtained average values ​​mostly similar to other studies of physical performance and sarcopenia, with some values ​​at the lower limit and others below expected levels, indicating a possible gradual decline in physical function and muscle health. It is important to assess muscle function from an early age to prevent the deterioration of physical fitness associated with XLH. Establishing our own reference values ​​is necessary for accurate comparison and preventive therapeutic interventions through physical activity.

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