Fatty Acid Oxidation

A 28-year-old man with a history of recurrent myoglobinuria and muscle pain triggered by prolonged fasting or intense exercise is found to have elevated serum creatine kinase (CK) and myoglobin in urine. Carnitine levels are normal. Genetic testing confirms a homozygous mutation in the CPT II gene. What is the most appropriate next step in management?

Which of the following enzymes catalyzes the first committed step of β-oxidation of fatty acids in mitochondria?

A 28-year-old woman with a history of recurrent rhabdomyolysis triggered by prolonged fasting and strenuous exercise presents with acute muscle pain and myoglobinuria. Serum CK is markedly elevated. Genetic testing suggests a defect in carnitine palmitoyltransferase II (CPT II). Which investigation is most specific for confirming impaired fatty acid oxidation capacity in skeletal muscle?

A 3-year-old boy from rural Maharashtra presents with recurrent episodes of hypoglycemia, lethargy, and hepatomegaly. His mother reports that symptoms worsen during fasting and improve after feeding. Laboratory investigations show: blood glucose 45 mg/dL (fasting), elevated liver transaminases (AST 120 U/L, ALT 110 U/L), normal ammonia levels, and markedly elevated serum free fatty acids (2.8 mmol/L). Urine organic acids show elevated dicarboxylic acids. A diagnosis of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is suspected. Which of the following best explains the pathophysiology of hypoglycemia in this child?

A 42-year-old man with poorly controlled type 2 diabetes presents with fatigue and fruity-smelling breath. Laboratory tests show elevated serum ketones and metabolic acidosis. Regarding ketone body metabolism during this state, all of the following are TRUE EXCEPT: