A novel recessive mutation of fibroblast growth factor-23 in tumoral calcinosis.

BACKGROUND

Tumoral calcinosis is a rare disease characterized by hyperphosphatemia due to hypophosphaturia and by ectopic calcifications. Phosphatonins are important hormones that regulate phosphorus homeostasis. Tumoral calcinosis is a rare congenital disorder in which the differential diagnosis from other syndromes associated with extraskeletal calcifications may be difficult. Mutations in the UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyltransferase-3 (GALNT3) and fibroblast growth factor-23 (FGF23) genes have been described. Mutational analysis is important for the early recognition of the disorder, for prevention of its complications, and for family screening strategies. We examined two unrelated white patients affected by tumoral calcinosis.

METHODS

The first patient was a woman with a history of an ectopic calcification in the left shoulder. The second patient was a man with a history of an ectopic calcification in the right buttock. Routine biochemistry and FGF-23 assays were performed on serum samples. Genomic DNA was extracted from peripheral blood. The FGF23 and GALNT3 genes were analyzed by direct sequencing.

RESULTS

A new homozygous H41Q codon 41, C-->A transversion at position 123 (c.123C>A) in exon 1 of the FGF23 gene was evidenced in both patients. No mutation of the GALNT3 gene was detected in these patients. As determined by an ELISA assay, intact FGF-23 circulating protein was low in both patients.

CONCLUSIONS

This is the fourth mutation of the FGF23 gene described in subjects with tumoral calcinosis.