Patient-reported outcomes measures of X-linked hypophosphataemia participants: findings from a prospective cohort study in the UK.

backgroundX-linked hypophosphataemia (XLH) is a rare genetic condition passed on through the X chromosome which causes multiple symptoms including weakened teeth, bones, and muscles. Due to the rarity of the condition, little is known about the health outcomes as reported by people with the disease. The objectives of this study were threefold: to characterise key patient reported outcome measures (PROMs) in adults with XLH, to identify clusters of symptom-severity groups based on PROMs, and to analyse the longitudinal progression of available PROMs.

methodsData from 48 participants from the Rare and Undiagnosed Diseases cohort Study (RUDY) was used to analyse both cross-sectional and longitudinal patient-reported outcomes. We analysed data for health-related quality of life (HRQL): EuroQol 5 dimensions-5 levels (EQ-5D-5L), Short-form 36 (SF-36) Physical Component Score (PCS), and SF-36 Mental Component Score (MCS), sleep: Pittsburgh sleep quality index (PSQI) and Epworth Sleepiness scale (ESS), fatigue: Fatigue Severity Scale (FSS) and Functional assessment of chronic illness therapy-fatigue (FACIT-F), pain: Short form McGill pain questionnaire version 2 (SF-MPQ-2) and PainDETECT, and mental well-being: Hospital anxiety and depression scale (HADS) anxiety and depression. Summary statistics, tests of mean differences, mixed-effects models, and cluster analysis were used to describe and examine the various health dimensions of individuals with XLH.

resultsOverall mean scores were EQ-5D-5L = 0.65, SF-36-PCS = 32.7, and SF-36-MCS = 48.4 for HRQL, ESS = 5.9 and PSQI = 8.9 for sleep, FSS = 32.8 and FACIT-F = 104.4 for fatigue, SF-MPQ-2 = 1.9 for pain, and HADS-depression = 4.7 and HADS-anxiety = 6.2 for mental well-being. 7% reported neuropathic pain (PainDETECT). Whilst many adults with XLH reported good outcomes, extreme or severe problems were reported across all outcomes. Cluster analysis identified that adults with XLH could be divided into two distinct groups, one reporting worse (35.3%) and the other better outcomes (64.7%) (less pain, fatigue, depression, and higher levels of sleep). Longitudinal analysis showed that FACIT-F and HADS-anxiety scores worsened slightly over two years with statistically significant (p < 0.05) time coefficients (b =  - 2.135 and b = 0.314, respectively).

conclusionAlthough about two thirds of adult participants of the RUDY cohort with XLH report good health outcomes, for a considerable third much worse outcomes are reported. More research is needed to examine why some experience good and others poor health outcomes and the characteristics which identify them.