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  • Updated 03.25.2020
  • Released 11.11.1996
  • Expires For CME 03.25.2023

Medium-chain acyl-CoA dehydrogenase deficiency


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


Medium-chain acyl-CoA dehydrogenase deficiency is the most common inborn error 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. It is now included on newborn screening in the United States and many other developed nations. The author highlights the 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 (11; 16). The disorder was not identified until the early 1980s (50), but is now recognized as the most common of the genetic defects in fatty acid oxidation (05). It is the most frequent inborn error of metabolism in Caucasians, especially those of Western European descent. 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 (13). 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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