Medium-chain acyl-CoA dehydrogenase deficiency

Jerry Vockley MD PhD (Dr. Vockley of the University of Pittsburgh School of Medicine has no relevant financial relationships to disclose.)
Tyler Reimschisel MD, editor. (Dr. Reimschisel of Vanderbilt University has received contracted research grants from Shire.)
Originally released November 11, 1996; last updated July 5, 2018; expires July 5, 2021

This article includes discussion of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.


Medium-chain acyl-CoA dehydrogenase deficiency is the most common of inborn errors of metabolism in the United States Caucasian population. Diagnosed symptomatically, the morbidity and mortality are high, but outcome is significantly improved if patients are identified before the onset of symptoms. The author highlights new technologies that have made it possible to diagnose this condition in the newborn period in a cost-effective fashion. As a result, more patients will ultimately find their way into adult medicine and neurology clinics in the coming years.

Key points


• Medium-chain acyl-CoA dehydrogenase deficiency can be asymptomatic for many years and present suddenly during periods of metabolic stress.


• Treatment during acute illnesses consists of maintaining caloric intake with sugar-containing oral or parenteral fluids.


• Medium-chain acyl-CoA dehydrogenase deficiency is now reliably identified in newborn screening in all states in the U.S. and many countries.


Carnitine is rarely, if ever, needed to treat medium-chain acyl-CoA dehydrogenase deficiency.

Historical note and terminology

Medium-chain acyl-CoA dehydrogenase deficiency is an autosomal recessive inborn error of mitochondrial fatty acid beta-oxidation (Coates and Tanaka 1992; Hale and Bennett 1992). The disorder was not identified until the early 1980s (Stanley et al 1983), but is now recognized as the most common of the genetic defects in fatty acid oxidation (Bentler et al 2016). It is one of the most frequent inborn errors of metabolism. The medical literature prior to 1980 contains a number of references to patients who either were later proved to have medium-chain acyl-CoA dehydrogenase deficiency or probably had this disorder. The possibility of medium-chain acyl-CoA dehydrogenase deficiency should be considered in this older literature in patients described as having dicarboxylic aciduria, infantile Reye syndrome, and, particularly, either "systemic carnitine deficiency" or "primary carnitine deficiency." For example, 4 patients originally published as having "primary systemic carnitine deficiency" were later shown to have medium-chain acyl-CoA dehydrogenase deficiency (Engel et al 1981). The reason for this confusion is that medium-chain acyl-CoA dehydrogenase deficiency and several other genetic defects in acyl-CoA oxidation are associated with secondary carnitine deficiency. Caution must be taken in reviewing discussions of carnitine deficiency that were published between 1970 and 1982 because they may be outdated and can be misleading.

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