Fatty Acid Oxidation

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:

A 28-year-old woman with a 10-year history of progressive muscle weakness, myalgia, and recurrent rhabdomyolysis is found to have elevated plasma long-chain acylcarnitines, normal ammonia, and normal liver function. Muscle biopsy shows lipid storage myopathy. Genetic testing confirms very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. She is currently on a standard diet with no dietary restrictions. What is the most appropriate next step in management?