A 10-Year-Old Boy Has a Low Plasma Ionized Ca2+ and an Increased

question 2

Multiple Choice

A 10-year-old boy has a low plasma ionized Ca2+ and an increased parathyroid hormone level. He has a high plasma alkaline phosphatase, exhibits muscle weakness, and has skeletal areas that are poorly calcified. You prescribe vitamin D3, but see no improvement. However, treatment with 1,25(OH) 2-vitamin D3 causes the patient's ionized Ca2+ level to increase. What would the most likely diagnosis be?

• A) Type 1 vitamin D-dependent rickets
• B) Rickets due to vitamin D deficiency
• C) Inability to form 24(OH)-vitamin D₃
• D) Receptors for dehydrocholesterol are absent
• E) Inability to form vitamin D₃ in the skin

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