A boy presented after his gross motor development plateaued at around 1 year of age. He sat unsupported at 8 months, cruised and could stand unsupported at 12 months with minimal progression thereafter.

A detailed history revealed that he was easily fatigued by the end of the day, generally quite unsettled and his mother had noticed his wrists were quite swollen with a prominent clavicle (figure 1 and figure 2). His weight was on the 50th centile, length was 0.4th centile and head circumference was on the 75th centile, respectively. There were no significant family history and no dietary concerns.

Patient's clavicles

Baseline investigations revealed an adjusted calcium of 1.6 mmol/L (normal range 2.2–2.7 mmol/L), phosphate 0.95 (normal range 0.9–1.8 mmol/L), alkaline phosphatase (ALP) 1631 U/L (normal range 60–425 U/L). Parathyroid hormone was 214 ng/L (normal range 15–65 ng/L). …