Following a minor respiratory illness, a seemingly healthy, developmentally normal 15-month-old boy exhibited repeated episodes of severe lethargy and vomiting following periods of fasting, such as during the middle of the night. The parents brought the infant to the ER following a seizure. The child was hypoglycemic and was administered 10% dextrose, but remained lethargic. Blood ammonia was high, liver function tests were slightly elevated, and his serum contained an accumulation of dicarboxylic acids. Only low levels of ketones were detectable in the urine. This infant suffers from which of the following disorders?

Question

Quizplus · Accepted Answer

The symptoms and biochemical findings are consistent with Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, a disorder of fatty acid oxidation. It is characterized by hypoketotic hypoglycemia, elevated dicarboxylic acids, and high blood ammonia levels following fasting or illness.  Deficiency in MCAD is the most common inherited defect in the pathways of mitochondrial fatty acid oxidation. The most common presentation of infants with this disorder is episodic hypoketotic hypoglycemia following periods of fasting. Although the first episode may be fatal, and incorrectly ascribed to sudden infant death syndrome, patients with MCAD deficiency are normal between episodes and are treated by avoidance of fasting and treatment of acute episodes with intravenous glucose. Accumulation of acylcarnitines (dicarboxylic acids) is diagnostic, in particular octanoylcarnitine.

Following a Minor Respiratory Illness, a Seemingly Healthy, Developmentally Normal