The study by Gompertz et al. (42) performed PCC and MCM enzyme activity assays on mitochondria isolated from post-mortem liver in a patient with fatal “propionic acidemia.” Gompertz et al. found the level of PCC in the patient to be 9.7% that of controls, whilst MCM activity was normal, definitively localizing the enzymatic defect in PA to PCC. This evidence concerns the gene MMUT and propionic acidemia.