FGF23

At least three mutations in the FGF23 gene have been found to cause a rare form of hereditary hypophosphatemic rickets known as autosomal dominant hypophosphatemic rickets. These mutations change single protein building blocks (amino acids) in fibroblast growth factor 23, which prevents the protein from being cleaved. As a result, the protein is not inactivated, and an increased amount of the full-length, active protein circulates in the bloodstream. Overactivity of fibroblast growth factor 23 reduces phosphate reabsorption by the kidneys, leading to low levels of phosphate in the blood (hypophosphatemia) and related problems with bone growth in people with autosomal dominant hypophosphatemic rickets.

At least seven mutations in the FGF23 gene have been found to cause hyperphosphatemic familial tumoral calcinosis (HFTC), a condition characterized by an increase in the levels of phosphate in the blood (hyperphosphatemia) and abnormal deposits of phosphate and calcium (calcinosis) in the body's tissues. Mutations in the FGF23 gene lead to the production of a protein with decreased function. This nonfunctional protein is quickly broken down in cells, leading to a shortage of available fibroblast growth factor 23. This protein shortage decreases signaling and increases the amount of phosphate that is reabsorbed back into the bloodstream by the kidneys, leading to hyperphosphatemia. Calcinosis results when the excess phosphate combines with calcium to form deposits that build up in soft tissues.

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