A 3-year-old boy has progressive genu varum and short stature. His father had similar deformities corrected in childhood. Serum calcium is 9.6 mg/dL, phosphate is 2.0 mg/dL, alkaline phosphatase is elevated, and 25-hydroxyvitamin D is 32 ng/mL. Urinary phosphate excretion is excessive.

• A Nutritional vitamin D deficiency rickets treated with high-dose vitamin D alone
• B X-linked hypophosphatemic rickets treated with oral phosphate and calcitriol ✓
• C Vitamin D dependent rickets type II treated with calcium infusion
• D Renal tubular acidosis treated with alkali therapy

Explanation

X-linked hypophosphatemic rickets results from PHEX mutations causing renal phosphate wasting. The hallmarks are hypophosphatemia with normal calcium, normal 25-hydroxyvitamin D, elevated alkaline phosphatase, and male-to-female transmission through affected fathers. Treatment is oral phosphate combined with calcitriol to prevent secondary hyperparathyroidism. Nutritional rickets shows low 25-OH-vitamin D and often low calcium, vitamin D dependent rickets type II shows elevated 1,25-dihydroxyvitamin D with alopecia, and distal RTA presents with metabolic acidosis and nephrocalcinosis.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.