This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolic Disorders of Bone, Subject name: Orthopaedics
The following serum levels: calcium- 7.8 mg/ dL, 25 hydroxy vitamin D is high, 1 a-hydroxylase levels are low. Which drug shall be the most appropriate for treatment of this condition? 
Select and explain. 
A. Calcitriol, B. Phosphate supplementation, C. Calcifediol, D. Vitamin D3
A: Calcitriol
Answer: A: Calcitriol 
Explanation: The above scenario is of vitamin D dependent rickets type 1. VITAMIN D DEFICIENCY RICKETS Autosomal recessive Presents as childhood rickets | Calcium and | activity of 1a hydroxylase Do not respond to conventional doses of vitamin D. Rx- Calcitriol (0.25-0.5 mcg daily).