Approximately 60% of symptomatic homozygous patients present with a missense mutation in ACADM (c.985A > G) in which lysine is exchanged for glutamate at position 304, ultimately resulting in complete protein misfolding and loss of function (Figure 4).27 Most MCADD patients are either homozygous or heterozygous for c.985A > G; heterozygous patients may have a mild phenotype, indicating there may be other factors contributing to both severity of presentation and age of onset.1, 28. Here, ACADM is linked to medium chain acyl-CoA dehydrogenase deficiency.