You are examining a 10-month-old male infant during a routine visit; you find that he has wide wrists. He is still breast fed. X-ray of the wrist joint shows signs of rickets. Of the following, the BEST reflection of vitamin D deficiency is

Correct Answer: D

Rationale: Serum 25-hydroxyvitamin D is the best indicator of vitamin D status, reflecting stores and deficiency in rickets. Calcium (A), phosphate (B), PTH (C), and 1,25-hydroxyvitamin D (D) are affected but less direct measures.

Correct Answer: C

Rationale: Autosomal recessive PKD is characterized by marked bilateral renal enlargement, interstitial fibrosis, and early kidney failure, often with hepatic fibrosis leading to portal hypertension.

Correct Answer: D

Rationale: Type V (McArdle) has a good prognosis as it primarily causes exercise intolerance without systemic failure. Type 1a (A) and 1b (B) require careful management, type II (C) is fatal without treatment, and type IV (D) progresses to liver failure.

Correct Answer: A

Rationale: Transient tyrosinemia of the newborn, due to immature liver enzymes, resolves with ascorbic acid (vitamin C), which enhances tyrosine metabolism, unlike other vitamins or formulas.

Correct Answer: A

Rationale: Isovaleric acidemia produces a distinctive 'sweaty feet' odor from isovaleryl-CoA accumulation, unlike other listed disorders.