Exploring the Exercise and Physical Activity Experiences of Adults with X-Linked Hypophosphatemia

Abstract

Background: X-linked hypophosphatemia (XLH) is a rare hereditary phosphate-wasting disorder, marked by mutations in the PHEX gene on the X chromosome. Mutations result in renal phosphate wasting and decreased 1,25-dihydroxyvitamin D, leading to rickets in children and osteomalacia in adults. XLH contributes to significant physical impairments including lower limb deformities, reduced height, bone pain, stiffness, early osteoarthritis, and fractures, which collectively hinder mobility, physical functioning, and quality of life. Despite pharmaceutical treatments, mobility and physical functioning deficits remain inadequately addressed. Currently, there is not a strong understanding of how physical activity and exercise can affect health outcomes for people with XLH. XLH brings unique challenges to mobility and physical functioning which could bring its own barriers to exercise making it an important topic to explore to create interventions for the XLH population. Objective: The objective of the study was to understand the experiences of people with XLH when participating in physical activity and exercise. I looked to identify how having XLH affects participation in physical activity and exercise, the barriers to and facilitators of exercise and physical activity, and the health outcomes that are most important for people with XLH when making treatment decisions with medications, and exercise. Methods: Using a phenomenological approach from a post-positivism point of view, semi-structured interviews were conducted with adults diagnosed with XLH. The interview guide was designed using the COM-B model of behavior to reveal how capability, motivation and opportunity affects people with XLH’s exercise and physical activity behaviors. Data was analyzed using reflexive thematic analysis to understand the experiences during exercise and physical activity, the barriers to and facilitators of exercise, and the outcomes prioritized by participants. A content analysis was done to understand the most frequent modes of exercise being completed, and the patient important outcomes most prioritized to participants. Results: Semi-structured qualitative interviews, and two content analyses with 17 adults who have XLH were conducted. Pain, stiffness, and fatigue were identified as major barriers to both a person with XLH’s capability and motivation to participate in exercise and physical activity. Pain and stiffness created mobility limitations challenging a person’s capability. Fatigue and overexertion led to increases in pain and stiffness. The exacerbation of pain and stiffness from fatigue led to a fear of worsening symptoms affecting people’s reflective motivation to exercise. While fatigue worsens symptoms and discourages activity, participants described that when they were able to find the right balance of physical activity and exercise with rest they found improvements in pain, stiffness, mobility and overall physical functioning. Walking, stretching, swimming/water aerobics and strength training were completed most frequently by participants. Key facilitators to exercising were strategizing movement to manage fatigue, and tailoring exercise for mobility impairments. The study also highlights the importance of identifying patient important outcomes. Similar outcomes were identified for treatment with medications and exercise (pain, fatigue, strength mobility and physical functioning). But physical functioning and its individual components, such as strength, were more highly prioritized for exercise, versus pain for treatment with medications. Regardless of the context, improving functional outcomes and progression of the disease in the long-term was of the highest priority. Conclusion: While pain, stiffness, and fatigue pose substantial barriers to motivation and capability to participation in physical activity and exercise, the findings reveal that appropriately tailored and balanced exercise can lead to improvements in physical functioning, mobility, and symptom management. Participants emphasized the need for tailored approaches that account for their unique physical limitations, and for the management of fatigue. Crucially, the study underscores the significance of centering interventions around patient-prioritized outcomes which are often underrepresented in current clinical approaches. The findings lay the foundation for developing informed, person-centered physical activity guidance and exercise interventions that address both the physical and psychological challenges of living with XLH, ultimately aiming to improve quality of life and long-term health outcomes.