Question category: Endocrinology
A 2 year old is brought to his GP. His parents have noticed he is very small for his age. He has only just begun to walk and is not keen to. He complains of pain when he is walking. On examination there is evidence of frontal bossing of the skull and bowing of the legs. Bloods reveal a slightly low calcium, low phosphate and high alkaline phosphatase. There is increased urinary phosphate. What is the most likely diagnosis?