PTH challenge results in PHP Type 1A show:

PTH challenge results in PHP Type 1A show:

• A. Absence of normal increase in urinary cAMP
• B. Normal increase in urinary cAMP
• C. Decrease in urinary cAMP
• D. No change in urinary cAMP

Answer: (A)

The key idea is that PTH signals through the Gs protein to activate adenylyl cyclase in renal tubule cells, producing cAMP. In pseudohypoparathyroidism type Ia, there is end-organ resistance to PTH because of a defect in the Gs alpha subunit, so the kidney cannot generate the normal cAMP response to PTH. When a PTH challenge is given, the expected rise in urinary cAMP is blunted or absent. Therefore, the finding of no normal increase in urinary cAMP after PTH administration is characteristic of PHP type Ia, reflecting PTH resistance rather than a lack of PTH itself.

The key idea is that PTH signals through the Gs protein to activate adenylyl cyclase in renal tubule cells, producing cAMP. In pseudohypoparathyroidism type Ia, there is end-organ resistance to PTH because of a defect in the Gs alpha subunit, so the kidney cannot generate the normal cAMP response to PTH. When a PTH challenge is given, the expected rise in urinary cAMP is blunted or absent. Therefore, the finding of no normal increase in urinary cAMP after PTH administration is characteristic of PHP type Ia, reflecting PTH resistance rather than a lack of PTH itself.