Through this clinical case, we emphasize the importance of a complete phosphocalcic balance in order to find and recognize the typical biochemical alterations associated with this pathology (hypocalcemia, hyperphosphatemia and high levels of PTH), the need for a detailed clinical examination because the phenotypic appearance often escapes notice and the identification of the responsible mutation in the index case is useful for screening other family members avoiding late diagnosis. The gene discussed is PTH; the disease is hyperphosphatemia.