ACADM and medium chain acyl-CoA dehydrogenase deficiency: Clinical observation may support the hypothesis that the two most common mutations in the ACADM gene causing the amino acid substitutions p.Lys329Glu, the predominant variant in symptomatic patients, and p.Tyr67His, a biochemically mild variant solely found in presymptomatic infants in NBS, form the two ends of a phenotypic spectrum in MCADD.