What is the main difference between Vitamin D deficiency rickets and Vitamin D dependent type 2 rickets?

What is the main difference between Vitamin D deficiency rickets and Vitamin D dependent type 2 rickets?

• A. In Vitamin D dependent type 2 rickets, 1,25(OH) vitamin D levels will be elevated
• B. In Vitamin D dependent type 2 rickets, PTH is suppressed
• C. Vitamin D deficiency shows elevated 25-OH vitamin D
• D. Vitamin D deficiency shows high 1,25(OH)2 vitamin D

Answer: (A)

The difference hinges on how the body handles the active vitamin D hormone and how the target tissues respond. In vitamin D deficiency rickets there isn’t enough vitamin D to begin with, so stores of 25-hydroxyvitamin D are low and the downstream active form may be low or inappropriately normal, with secondary hyperparathyroidism driving abnormalities. In vitamin D dependent type 2 rickets, the problem is resistance to the active hormone at the vitamin D receptor, so the body keeps producing more of the active form under PTH stimulation, leading to elevated 1,25-dihydroxyvitamin D levels despite hypocalcemia and rickets. That’s why elevated 1,25(OH)2D is the distinguishing finding for VDDR2. The other statements don’t fit: PTH is not suppressed in VDDR2, deficiency cases typically don’t show high 25-OH vitamin D, and vitamin D deficiency doesn’t characteristically present with high 1,25(OH)2 vitamin D.

The difference hinges on how the body handles the active vitamin D hormone and how the target tissues respond. In vitamin D deficiency rickets there isn’t enough vitamin D to begin with, so stores of 25-hydroxyvitamin D are low and the downstream active form may be low or inappropriately normal, with secondary hyperparathyroidism driving abnormalities. In vitamin D dependent type 2 rickets, the problem is resistance to the active hormone at the vitamin D receptor, so the body keeps producing more of the active form under PTH stimulation, leading to elevated 1,25-dihydroxyvitamin D levels despite hypocalcemia and rickets. That’s why elevated 1,25(OH)2D is the distinguishing finding for VDDR2. The other statements don’t fit: PTH is not suppressed in VDDR2, deficiency cases typically don’t show high 25-OH vitamin D, and vitamin D deficiency doesn’t characteristically present with high 1,25(OH)2 vitamin D.