Laboratory for Molecular Diagnostics
Center for Nephrology and Metabolic Disorders

Autosomal dominant hypophosphatemic rickets

Autosomal dominant hypophosphatemic rickets are characterized by renal phosphate wasting and bone abnormalities.

Epidemiology

The autosomal dominant rickets is less common than x-linked dominant hypophosphatemic rickets, so the prevalence is much less than 1:20,000.

Test Strategy

In patient with bone disease and typical radiological findings, routine laboratory testing reveals hypophosphatemia. Renal phosphat losses have to be confirmed by measuring tubular maximum reabsorption of phosphate per glomerular filtration rate. When malignant tumors are exluded, molecular genetic testing provides further diagnostic precision.

Clinical Findings

Clinical symptoms include short stature, bone pain, tooth abscesses, enthesopathy (calcification of tendon insertions, ligaments, and joint capsules), and lower-extremity deformities. Secondary to renal phosphate wasting, a hypophosphatemia is present. Renal phosphate losses are measured by the maximum tubular reabsorption per glomerular filtration rate. Serum calcitriol concentrations are inappropriately normal or low despite the prominent hypophosphatemia. Radiographic changes in children consists of the typical rickets signs which include fraying, widening, and cupping of the metaphyseal ends of long bones. In adults radiographic findings vary with disease severity. They can include pseudofactures, osteoarthritis, and enthesopathic changes. Bone biopsy reveals osteomalacia.

Differentials

The same clinical abnormalities can be caused by malignant tumors.

Systematic

FGF23-induced hypophosphatemic rickets
Autosomal dominant hypophosphatemic rickets
FGF23
Autosomal recessive hypophosphatemic rickets type 1
Autosomal recessive hypophosphatemic rickets type 2
X-linked dominant hypophosphatemic rickets

References:

1.

Brame LA et al. (2004) Renal phosphate wasting disorders: clinical features and pathogenesis.

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2.

Yu X et al. (2005) FGF23 and disorders of phosphate homeostasis.

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Update: Sept. 26, 2018