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X-linked Hypophosphatemia

Also known as: Familial Hypophosphatemic Rickets, Vitamin D Resistant Rickets


X-linked hypophosphataemia is a rare condition that causes low phosphate levels in the blood (hypophosphataemia), associated high phosphate excretion in the urine (hyperphosphaturia), and symptoms of rickets such as bowed or knock-kneed legs. Dental problems are also common. The gene that is changed (mutated) in this syndrome is called PHEX, and is located on the X chromosome. Diagnosis is made by blood tests, which show a low phosphate level and high alkaline phosphatase level. Treatment  involves improving the blood phosphate level using oral phosphate supplements, and an active vitamin D hormone such as  1-alpha D3 (alfacalcidol) or 1,25 D3 (calcitriol). Regular blood tests for phosphate and alkaline phosphatase levels, and ultrasound examination of the kidneys to check for calcium crystals as a side-effect of Vitamin D treatment, are part of the standard care associated with this condition. Occasionally, surgery is needed to shorten, lengthen, or change the angle of a leg bone. The gene causing the condition can be inherited, or the condition can occur sporadically (with no family history). Affected families should be referred to a specialist centre for information and support.

This overview is intended to be a basic description of the condition. It is not intended to replace specialist medical advice. We advise that you discuss your child's case with a qualified medical professional who will be able to give you more detailed information.


Medical text approved January 2013 by Dr C Reid, Paediatric Nephrologist, Evelina Children's Hospital and Dr M Champion, Contact a Family Medical Advisory Panel.

Is there support?

There is no support group for X-linked hypophosphataemia in the UK. A support group outside of the UK exists for X-linked hypophosphataemia, please ring our helpline for details. Contact a Family's web-based linking service can be accessed at