Clinical feature: 

Definition: Dominant x-linked hypophosphatemic rickets are characterized by renal phosphate wasting and bone abnormalities.

Epidemiology: X-linked dominant hypophosphatemic rickets is a common cause of rickets with a prevalence of approximately 1 in 20,000.

Clinical picture: 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.

Diagnostics: 

Differential: The same clinical abnormalities can be caused by malignant tumors, the autosomal dominant form of hypophosphatemic rickets, hypophosphatemic bone disease, and hypophosphatemia with hypercalciuria.

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.

Literature: 

Brame LA et al. (2004) Renal phosphate wasting disorders: clinical features and pathogenesis.
Baroncelli GI et al. (2004) Genetic advances, biochemical and clinical features and critical approach to treatment of patients with X-linked hypophosphatemic rickets.