Medium-chain acyl-CoA dehydrogenase (MCAD) is a homotetrameric flavoprotein which catalyses the initial step of theb-oxidationofmedium-chain in MCAD may cause disease in humans. A Y42H mutation is frequently found in babies identified by newborn screening with MS/MS, yet there are no reports of patients presenting clinically with this mutation. As a basis for judging its potential consequences we have examined the protein phe-notype of the Y42H mutation and the common disease-associatedK304E mutation. .
