Introduction Hypophosphatemic rickets is a rare genetic condition presenting with symptoms of rickets also characterised by its resistance to vitamin D and ultraviolet treatment. Its genotype involves a mutation in the PHEX gene which leads to down-regulation of FGF-23 which in turn leads to phosphate losses due to decreased tubular re-absorption in the kidneys.

Case Report A 10 month old girl was initially investigated by her GP for non-weight bearing confirmed on examination. Systemic examination was unremarkable. X rays then showed likely right hip coxa varus which was monitored by Othropaedics over the next few months. For possible metaphyseal dysplasia at 18 months was referred for paediatric opinion. Examination showed frontal bossing, harrison sulci, prominent metaphyses and mild hypotonia. Investigations confirmed hypophosphatemia, increased serum Alkaline Phosphatase and parathormone with Xrays suggestive of Rickets. Ergo-calciferol and phosphate supplementation were started showing biochemical and systemic improvement. Initial investigations for faltering growth returned normal. She was then referred for tertiary endocrinology review for continued poor growth and limited response to phosphate supplements. Investigations confirmed decreased tubular absorption of phosphate with persistent radiological findings of Rickets. On increasing phosphate supplement dosage she developed diarrhoea, an observed side effect of phosphate supplements. In view of poor growth and persistent diarrhoea she underwent further investigations with Endoscopy and biopsy confirming coeliac disease and was further supported by IgG positive Transglutaminase (previous negative IgA tissue transglutaminase). Gluten free diet and higher strength of phosphate supplement (Joules solution) were commenced leading to marked symptomatic improvement, improved motor milestones and growth. Recently she presented with persistent fatigue with sub optimal growth and investigations confirmed autoimmune hypothyroidism needing thyroxine. On subsequent reviews her growth and energy level improved.

Conclusion This case highlights the need to consider dual/triple diagnoses in rare disorders where despite adequate therapy there is limited improvement and there are sure signs/symptoms of another disorder.