Bone Abstracts

Background: Hypophosphataemic rickets is a rare form of rickets characterised by hypophophatamaemia and hyperphosphaturia. Children can present with bowed legs, gait abnormalities or persisting rickets. Occasionally the clinical and biochemical features may be mild. It is most commonly caused by a mutation in the phosphate-regulating endopeptidase homolog, X-linked (PHEX) gene which leads to an elevated FGF23.

Objectives: We wished to review our cohort of chidren with hypophosphataemic rickets, both their clinical and bichemical findings and their surgical management.

Methods: All current patients in our service were identified and their notes, results and correspondance retrospectively reviewed.

Results: Ten children (six female, four male) (three Asian, seven Caucasian) with hypophosphataemic rickets were identified. Four had a family member with hypophosphataemic rickets leading to a diagnosis within the first year. Six of the other index cases had a confirmed diagnosis at median age 4.6 years (range 3.7–15 years). All children had low or low normal plasma phosphate levels. FGF23 was available for seven children and was raised in all but one child: Range 85–618 RU/ml (normal range <100). The 1,25 Vit D levels were inappropriately normal or marginally raised. Genetic confirmation was obtained for five children. Four of them had a mutation in the PHEX gene and one child had an Ectonucleotide Pyrophosphatase/Phosphodiesterase 1 (ENNP1) mutation. One child had craniosynostosis, one had coeliac disease. All children were treated with a combination of phosphate sandoz and alfacalcidol. Four (two female) children had orthopaedic surgery to correct their bowed legs, half of whom had a family history of hypophosphataemic rickets and the other half were index cases. One adolescent was eligible for surgery but refused.

Conclusion: Half of our children were eligible for orthopaedic surgery, with no clear sex bias. ENPP1 mutations can be associated with generalised arterial calcification thus pursuing a genetic diagnosis is important. The biochemical abnormalities may be mild and thus delay a diagnosis, so it is imperative that those with low plasma phosphate levels and persistence of gait abnormalities or bowed legs are investigated thoroughly for hypophosphataemic rickets.

Disclosure: The authors declared no competing interests.