Hypophosphataemic rickets

Hypophosphataemic rickets is a hereditary form of rickets (most commonly X-linked dominant). It is often recognised from family history. It can also be recognised in infants aged 6 to 12 months old who develop bowing of the legs in the absence of vitamin D deficiency. The diagnosis is confirmed by:

• low serum phosphate concentration
• serum calcium concentration at the lower end of the normal range
• elevated serum alkaline phosphatase
• reduced fractional kidney phosphate reabsorption
• radiological evidence of rickets.

Specialist management is required. Early and consistent therapy with high-dose oral phosphate and calcitriol allows bone mineralisation with straighter limbs and facilitates optimal growth, while minimising secondary hyperparathyroidism. See also Hypophosphataemia.

The aim of therapy is to maximise growth rather than to normalise the serum phosphate concentration. With adequate therapy, rickets should resolve and the serum alkaline phosphatase should return to a normal or near-normal concentration.

Treatment may need to be continued into adulthood—adults with X-linked hypophosphataemic rickets often have osteomalacia and skeletal symptoms.