An 8-month-old female infant is brought to the ER because her parents have been unable to fully rouse her for 3 hours. She had repeated episodes of vomiting and diarrhea the previous day, and she has not eaten for the past 12 hours. Physical examination shows lethargy and mild hepatomegaly. Serum and urine studies show no ketones. There is an abnormally increased ratio of acylcarnitine to free carnitine in urine. Which of the following is the most likely diagnosis?

Question

Quizplus · Accepted Answer

The symptoms and laboratory findings are consistent with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, a disorder of fatty acid oxidation. The absence of ketones despite fasting and the increased acylcarnitine to free carnitine ratio are indicative of this condition.  The most common symptom of MCAD deficiency is episodic hypoketotic hypoglycemia brought on by fasting. Symptoms appear within the first 2 years of life. Clinical crisis is characterized by an infant presenting with episodes of vomiting and lethargy that may progress to seizures and ultimately coma. Because the capacity of the gluconeogenesis pathway is limited in newborn infants, they are highly susceptible to the lack of brain energy from the ketones that would normally be derived from fatty acid oxidation.

An 8-Month-Old Female Infant Is Brought to the ER Because