Living in the Gaps: What the XLH Patient Journey Tells Us About Rare Disease Care in the UK

X-linked hypophosphataemia isn't a condition most people have heard of. It's a rare inherited disorder of phosphate regulation that causes progressive bone and muscle problems throughout life — and for many patients, the adult years are when the cumulative toll really hits.

medintel conducted a qualitative study involving UK physicians across endocrinology, rheumatology, metabolic bone disease, and nephrology to map out what the patient pathway actually looks like. The picture that emerges is one of localised improvisation, variable quality, and a treatment landscape that too often leaves patients treading water.

Getting to a Diagnosis

For most adults with XLH, the road to diagnosis starts with something non-specific — persistent pain, fatigue, a fracture — and a GP who may or may not connect the dots. Around 90% of patients are diagnosed in childhood and transition into adult services; for the remaining 10% or so, the adult diagnosis tends to come in their twenties, though it can be much later. In childhood, misdiagnosis is common: rickets, growing pains, poor nutrition. In adults, the differential is broader — ankylosing spondylitis, rheumatoid arthritis, fibromyalgia, vitamin D deficiency all get in the way. Low phosphate, physicians stressed, is the key diagnostic signal that unlocks everything else.

Diagnostic access is not uniform. Genetics testing — useful for confirming PHEX mutations and cascade family screening — is not available at every District General Hospital. FGF23 levels aren't tested everywhere. The physicians who work at regional specialist centres had notably more confidence in their diagnostic toolkit and referral pathways than those based at DGHs, who reported working with fewer resources and less joined-up multi-disciplinary support.

A Pathway Built on Local Luck

There is no single national blueprint for managing adult XLH. Which specialty takes the lead — endocrinology or rheumatology — appears to depend largely on who happens to work at a given hospital and what their clinical interests are. As one metabolic bone specialist put it bluntly: it's historical. Where an interested endocrinologist built up a cohort, endocrinology runs it. Where a rheumatologist did, rheumatology does.

Multi-Disciplinary Teams, where they exist, are described as inconsistent and ad-hoc. In specialist regional centres, a dedicated specialist nurse often acts as a care coordinator for patients with rare genetic bone disorders — a role that makes a meaningful difference to continuity. But outside those centres, that role simply doesn't exist. The concept of "expert centres" is itself murky: physicians had differing views on what designates one, with references to ERN Endo, ERN Bone, and approved rare disease sites. A loose network of centres — Sheffield, Leeds, the Royal Free, Cambridge, Oxford and others — is understood to carry disproportionate expertise, but formal designation remains unclear.

Transition from paediatric to adult care follows NICE guidelines in principle, though these weren't front of mind for at least half the physicians. In practice, the transition typically spans six to nine months between ages 16 and 18, ranging from a simple referral letter to joint clinics involving both adult and paediatric teams. Physicians at specialist centres were generally more confident in the process. Most considered their own local approach adequate, even where they acknowledged wider systemic shortcomings.

The Treatment Problem

The most consistent frustration in the study is conventional therapy — oral phosphate supplements and active vitamin D. Most adult patients remain on it, not because it works well, but because burosumab, despite being licensed, was not accessible to these physicians' patients at the time of the study. The side-effect profile of conventional treatment is significant: GI intolerance, the risk of nephrocalcinosis if over-treated, and compliance problems driven by high pill burden and unpleasant taste. Physicians estimated around 70% of patients experience some side effects. The result is a slow, demoralising attrition of patient engagement.

Patient disengagement is a recognised feature of the landscape. When treatment isn't helping, appointments feel pointless. Patients — particularly adolescents navigating university, new jobs, changing geography — disengage. NHS trusts typically operate a "two strikes" discharge policy: miss two appointments, get sent back to primary care. Those who disengage tend to return to the system eventually, but usually via orthopaedics, pain management, or A&E, rather than through planned care.

What This Means

The physicians in this study weren't sounding alarms about catastrophic care failures. Most felt their patients were broadly managed adequately — "they don't get lost in the system" was a phrase that recurred. But adequacy is a low bar. The structural inequality between specialist centres and DGHs, the absence of consistent MDT provision, the dependence on individual clinician interest, and the limitations of conventional therapy all point to a system that delivers satisfactory care despite itself, rather than by design. For a rare disease population that lives with progressive, lifelong symptoms, that distinction matters.

About the Research

This research was sponsored by a donor and the results were designated for public circulation.

medintel is a specialist medical market research consultancy. For more information, contact intel@medintel.co.uk.

medintel conducts larger-scale quantitative and qualitative research across healthcare professional populations. If you're interested in more on rare disease research, please get in touch.