MCQ – 87305

The only variety of rickets in which parathyroid hormone (PTH) levels are normal is:

A.	Nutritional
B.	Vitamin D resistant
C.	Vitamin D-dependent Type 1
D.	Vitamin D-dependent Type 2

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Correct Answer � B Explanation

Ans.B. In vitamin D-resistant rickets, renal tubule’s inability to retain phosphate results in loss of excessive phosphate through urine. Therefore, even normal or higher supplementations of vitamin D are not sufficient for bone mineralization.

In Vitamin D resistant rickets:

• Serum calcium level is normal.
• Serum phosphorous level is reduced.
• Alkaline phosphatase is increased.
• Urine phosphorus is increased.

Examples include Fanconi’s syndrome.

• Since calcium levels are not decreased, parathormone levels remain normal making this a characteristic feature of this type of rickets.
• Vitamin D-dependent Type 1 rickets is due to decreased activation of vitamin D to its active form in kidney.
• Vitamin D-dependent Type 2 rickets is due to resistance to vitamin D in peripheral tissues. This resistance to Vitamin D can be overcome with high levels of this vitamin by supplementation.