From hypercalcemia to the diagnosis of pseudohypoparathyroidism type 1b: a case report.

Pseudohypoparathyroidism type 1b (PHP-1b) is a rare genetic disorder caused by mutations or epigenetic alterations of the maternal GNAS gene, resulting in isolated renal resistance to parathyroid hormone (PTH) and, in some cases, partial resistance to thyroid-stimulating hormone. Clinical manifestations typically result from hypocalcemia and resemble those seen in hypoparathyroidism, while laboratory tests show elevated serum PTH levels along with hypocalcemia and hyperphosphatemia. We present a case of a girl with an unusual course of PHP: from non-autoimmune hypothyroidism coexisting with hypercalcemia at the age of 1 year to the diagnosis of PHP-1b at the age of 3.5 years, before the onset of symptomatic hypoparathyroidism. In the absence of a clear cause for hypothyroidism, assessment of calcium and phosphate metabolism should be considered. Initial hypercalcemia does not exclude the diagnosis of PHP-1b. Long-term monitoring of calcium and phosphate metabolism parameters may be necessary for a final clinical diagnosis.