You are asked to consult about a 2-month-old girl with hypotonia, seizures, and an elevated plasma lactate (8 mM/L, normal <2). Brain MRI shows a thin corpus callosum but no other abnormalities. You suspect pyruvate dehydrogenase deficiency. Which of the following is the most likely mode of inheritance in this infant?

Correct Answer: C

Rationale: Pyruvate dehydrogenase deficiency (PDH) is often autosomal recessive (C), though X-linked forms exist. Rationale: E1 subunit mutations (PDHA1, X-linked) are common, but autosomal recessive (other subunits) fits sporadic cases in females without male bias; symptoms match metabolic defect.

Correct Answer: D

Rationale: Mastodynia (breast pain) is typically cyclical, related to the menstrual cycle; ‘unrelated’ (D) is incorrect, but options suggest cyclical is absent, making D the best fit. Rationale: Cyclical mastodynia peaks premenstrually; noncyclical (C) is less common and not size-dependent (A).

Correct Answer: C

Rationale: The human genome has ~3.1 billion base pairs (A), ~20,000–25,000 genes (B), and non-coding 'junk' DNA doesn’t directly form proteins (D). Only ~1.5–2% is coding DNA, not 60% (C is false). Rationale: Most DNA is non-coding, with regulatory or unknown roles.

Correct Answer: A

Rationale: Losartan (A), an ARB, reduces aortic root dilatation in MFS. Rationale: It targets TGF-β signaling (FBN1 defect); beta-blockers like atenolol (B) are older options.

Correct Answer: D

Rationale: Cleft lip (A), spina bifida (B), asthma (C),; hairy ear (D) is simpler, often Y-linked or single-gene. Rationale: Polygenic traits involve multiple genes plus environment.