A 5-year-old boy from upper socioeconomic back- ground presents with bowing of legs. On work up serum calcium was 9 mg% with serum phosphate of 1 mg% with normal SAP and normal Serum PTH. X-ray Wrist joint is given. Comment on the diagnosis?

Ans. (a) Hypophosphatemic rickets.* The X-ray wrist shows cupping and splaying of distal end of radius. However serum calcium is normal with normal SAP ruling out nutritional rickets.* However the radiological findings can be explained by low phosphate levels secondary to phosphate wasting. In hypophosphatemic rickets due to PHEX-1 gene phosphate depletion leads to depletion of hydroxyapatite in the bone which weakens the bone leading to rickets and bowing of legs. Image source. style="font-size: 1.04761904761905em; color: rgba(0, 0, 0, 1); font-family: Times New Roman, Times, serif; margin: 0 0 8pt">