X-Linked hypophosphatemic rickets: a disease often unknown to affected patients

X-Linked hypophosphatemic rickets (XLH) is an X-linked dominant disorder that is secondary to renal phosphate wasting. Affected individuals frequently present the following characteristics: short stature, lower-extremity deformity, bone pain, dental abscesses, en-thesopathy, rickets, and osteomalacia. Since the disorder is characterized by evident phenotypic abnormalities, we hypothesized that there would be a high degree of knowledge about the disease in affected kindreds. Thus, we constructed a six-page, self-administered questionnaire to determine whether family members are, in fact, aware of their disease and properly diagnosed and treated. We also designed the survey to determine rates of symptoms thought to be associated with rickets/osteomalacia in a population with a lower referral bias than is usually seen in tertiary care centers. We administered the questionnaire to 234 study subjects (57 affected) who were members of one of three large kindreds. Although 62% of affected individuals knew they had some problem with their bones, only 22.6% were told by a physician that they had rickets or osteomalacia. This apparent lack of awareness occurred in spite of 61.1% of affected subjects complaining of bone or joint problems to their personal physician. Indeed, of those patients who had persistent complaints, only 34.5% were told they had rickets or osteomalacia. Only one patient was taking phosphate and vitamin D. The spectrum of symptoms evident in affected subjects compared with normals included: dental abscesses (54.5% vs. 13.0%, P < 0.001), bone pain (45.5% vs. 28.2%, P = 0.027), back pain (51.8% vs. 35.1%, P = 0.036), joint stiffness (48.2% vs. 16.8%, P < 0.001), joint pain (55.4% vs. 31.1%, P = 0.003), weakness (25.0% vs. 10.7%, P = 0.023), and hearing loss (28.6% vs. 9.8%, P = 0.002). Surprisingly, although affected individuals complained of many symptoms due to XLH, they fractured bones less frequently than controls (20% vs. 38.1%., P = 0.018). Our data demonstrate that, despite the presence of disease in family members, few affected subjects knew that they had XLH. Although the presence of symptoms did increase knowledge of disease status, only one-third of symptomatic individuals knew of their diagnosis.