A 6-year-old girl is brought to office due to prolonged fatigue and difficulty walking. Her childhood developmental growth was normal but rapidly becomes weak and tired. The patient has not been ill recently and is usually happy and playful. She has a history of mild motor delays but is otherwise developmentally normal. Vital signs are within normal limits. Examination shows mildly decreased power in all extremities but no ataxia. Cardiac auscultation reveals a 1/6 systolic murmur and an S3 gallop. Laboratory results are as follows: Muscle biopsy shows a very low carnitine content. This patient most likely has deficient synthesis of which of the following substances?

Question

A 6-year-old girl is brought to office due to prolonged fatigue and difficulty walking. Her childhood developmental growth was normal but rapidly becomes weak and tired.  The patient has not been ill recently and is usually happy and playful.  She has a history of mild motor delays but is otherwise developmentally normal.  Vital signs are within normal limits.  Examination shows mildly decreased power in all extremities but no ataxia.  Cardiac auscultation reveals a 1/6 systolic murmur and an S3 gallop.  Laboratory results are as follows:  Muscle biopsy shows a very low carnitine content.  This patient most likely has deficient synthesis of which of the following substances?

Quizplus · Accepted Answer

Eductional Objective: Carnitine deficiency impairs fatty acid transport from the cytoplasm into mitochondria, preventing Beta-oxidation of fatty acids into acetyl CoA.  This leads to cardiac and skeletal myocyte injury (lack of ATP from citric acid cycle) and impaired ketone body production by the liver during fasting periods.

A 6-Year-Old Girl Is Brought to Office Due to Prolonged