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Hypophosphataemic rickets

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Hypophosphataemic rickets is characterised by growth retardation, rickets or osteomalacia, hypophosphataemia, and renal defects in phosphate reabsorption and in vitamin D metabolism.1 The X-linked form (X-linked dominant) is the most common with a defect in phosphate transport in the proximal tubule leading to persistent hypophosphataemia and high levels of phosphate in the urine. Much rarer autosomal dominant, recessive, and sporadic forms also occur.

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Epidemiology

  • Rare.

  • The degree of bone involvement is much less severe in heterozygous females. However, there is often a maternal as well as paternal family history of short stature.2

Presentation2

  • Slow growth rate in the first year of life.

  • Reluctance to weight-bear when beginning to stand or walk.

  • Late dentition, multiple dental abscesses.

  • Intellectual development is unaffected.

  • Widened joint spaces and flaring at the knees may become apparent in children by their first birthday, particularly in boys.

  • When a child begins to stand and walk, bowing of the weight-bearing long bones develops quickly.

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Differential diagnosis

  • Cystinosis.

  • Tyrosinaemia.

  • Renal tubular acidosis.

  • Hereditary hypophosphataemic rickets with hypocalciuria.

  • Fanconi's syndrome.

  • Vitamin D-deficient rickets.

  • Pseudohypoparathyroidism.

Investigations

  • Urinary loss of phosphate is increased because of decreased renal tubular reabsorption of phosphate.

  • Blood tests for serum calcium, phosphate, alkaline phosphatase and parathyroid hormone:

    • Serum calcium levels may be normal or slightly low.

    • Phosphate levels are low.

    • Alkaline phosphatase levels are increased.

    • Parathyroid hormone level is normal or slightly raised.

  • X-rays of the wrists, knees, ankles, and long bones: no pathognomonic signs distinguish hypophosphataemic rickets from any other aetiology.

  • Periodic renal ultrasound is important to monitor for development of nephrocalcinosis.

  • Monitoring the ratio of calcium to creatinine in the urine is also important (a urinary ratio of calcium to creatinine more than 0.25:1 requires reduction of the vitamin D dosage to avoid nephrocalcinosis).

  • Patients under treatment should be carefully monitored for evidence of hyperparathyroidism.

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Management

  • Calcitriol (1,25-dihydroxycholecalciferol) - standard vitamin D preparations are not effective.

  • In some poorly growing patients, long-term growth hormone therapy given with conventional treatment improves linear growth.3

  • Calcitriol reduces but does not eliminate the risk of hypercalcaemic episodes, which may be frequent with vitamin D treatment.2

  • Amiloride and hydrochlorothiazide are given to increase calcium reabsorption and reduce the risk of nephrocalcinosis.2

  • Phosphate replacement is required because of the large urinary phosphate loss.

  • Osteotomy may be necessary for children whose diagnosis was delayed or whose initial treatment was inadequate.

  • Skull deformity may require treatment for synostosis.

  • Dental abscesses often require dental treatment.

Complications

  • Short stature, which is disproportionate, resulting from deformity and growth retardation of lower extremities.

  • Acute hypercalcaemia may occur during treatment.

  • Nephrocalcinosis, which does not usually progress to renal failure.

  • Hypertension may occur as a result of persistent hyperparathyroidism.

Prognosis

  • X-linked hypophosphataemic rickets is frequently associated with short stature, even when treatment is provided for a long time.3

  • Apart from the short stature, the prognosis is usually good with a normal lifespan.

Further reading and references

  1. Hypophosphatemic Rickets, X-linked Dominant, XLHR; Online Mendelian Inheritance in Man (OMIM)
  2. Roth KS; Hypophosphatemic Rickets, eMedicine, Feb 2009
  3. Saggese G, Baroncelli GI; Hypophosphataemic rickets. Horm Res. 2000;53 Suppl 3:57-60.

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Article history

The information on this page is written and peer reviewed by qualified clinicians.

  • 20 Apr 2011 | Latest version

    Last updated by

    Dr Colin Tidy, MRCGP

    Peer reviewed by

    Patient clinician team
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