According to a study published on March 22, 2023 in the scientific journal Frontiers in Endocrinology, the rare genetic disorder X-linked hypophosphatemia (XLH) has a negative impact on the function of the ankles. While it has long been understood that the function of the lower limbs is adversely impacted by the disease, this study sought to gain more in-depth insight into how the ankles and their function were impacted.

About X-linked Hypophosphatemia (XLH)

X-linked hypophosphatemia (XLH) is a genetic disorder. It is considered a type of rickets that is distinguished from dietary deficiency forms of rickets because vitamin D cannot cure it. Rickets is characterized by the abnormal softening of bones which can result in a bow-legged appearance and stance. The disorder is linked to mutations affecting the PHEX gene sequence found on the X chromosome. Symptoms of X-linked hypophosphatemia include soft bones, bone pain, osteoarthritis, teeth problems, and hearing loss. Treatment may include burosumab (as of 2018), calcitriol, phosphate, human growth hormone (HGH), and surgery to correct bowed legs or other bone deformities. The prevalence of this disease is about one in every 20,000 people. To learn more about X-linked hypophosphatemia, click here.

The Study

Data from 23 adult patients with the disorder was utilized in the study. These patients had genetically verified diagnoses and a total record of radiographic analysis and gait analysis. This data, which consisted of gait analysis, radiological analysis, and clinical examination, was compared with norms from a gait laboratory registry. In comparison to the norm, patients had substantially worse plantar flexion, ankle power, and gait quality. 30% of the patients had ankle varus deformity and 22% had ankle valgus deformity.

Joint space narrowing was also prevalent among the patients, reducing ankle strength/power. The subtalar joint was impacted in 59.1% of patients and the anterior tibiotalar joint was involved in 31.1%. Other factors that contributed to reduced ankle strength included clinical ankle restriction, tibial procurvatum deformity, and subtalar ankle osteoarthritis. 

This study identified a number of factors that contributed to ankle weakness and pain. The authors state that further research should investigate the influence other aspects, such as the effect of burosumab therapy (beginning early in life) and the impact of foot-specific pathologies.