Dear Dr. Roach: My grandson is 26 years old and has a rare disease called pseudohypoparathyroidism. The only doctor in our area who knows this disease has only ever seen one case. The medicine my grandson is on is not working and causes bad headaches. His back hurts. He also has blood in his urine and can’t work. He takes .5 milligrams of calcitriol but his calcium is still low. He takes 3 grams of calcium a day. Can you give me any information about this disease? — G.P.J.
Answer: Parathyroid hormone raises calcium levels in the blood by increasing dietary absorption, forcing the bones to release calcium and reducing the amount of calcium excreted by the kidney. Without parathyroid hormone, calcium levels in the blood may become dangerously low. This is called hypoparathyroidism. It is quite rare as a genetic condition, but can happen after surgery on the thyroid or parathyroid glands.
Pseudohypoparathyroidism is low calcium levels but above-normal PTH levels. It is normally caused by resistance to the effects of PTH by kidney or bone. The PTH levels are above normal because the body tries to compensate for this resistance to PTH. The cause is most commonly a damaged gene called GNAS1, and if inherited from the mother, the kidney is the primary site of resistance.