X-linked hypophosphataemic rickets

- dominantly inherited (transmitted by affected father to all daughter)
- defect in renal phosphate handling 
- mutation in the PEX or PHEX genes which encode an endopeptidase
- rickets develops in early childhood and is associated with poor growth
- low phosphate, high PTH, high urine phosphate
- treatment: high dose oral phosphate and vitamin D (calcitriol)