Pseudohypoparathyroidism is best described as which of the following?

• A. Heredity disorder of target-organ unresponsiveness to PTH
• B. PTH receptor deficiency
• C. PTH secretion by tumors
• D. Autoimmune destruction of parathyroids

Answer: (A)

Pseudohypoparathyroidism is defined by end-organ resistance to parathyroid hormone. The body makes PTH, often in normal or elevated amounts, but the kidneys and bones don’t respond properly because the signaling pathway after the receptor is defective. This resistance leads to low calcium and high phosphate in the blood, with inappropriately high PTH levels. Because it is usually inherited, describing it as a hereditary disorder of target-organ unresponsiveness to PTH captures both the mechanism and the inheritance pattern. The other scenarios don’t fit: a receptor deficiency would imply the receptor itself is faulty, which is a more specific and less accurate way to describe the resistance here; PTH secretion by tumors would raise PTH or PTH-related peptide and typically cause hypercalcemia; autoimmune destruction of the parathyroids diminishes PTH production, causing hypocalcemia without resistance.