ARD was first identified in the methionine salvage pathway of the bacterium Klebsiella, as part of an effort to better understand mechanisms of methionine metabolism.[1] It had been known for some time that, unlike the cell lines from which they are derived, many carcinomas are either strictly or partially dependent on an external supply of methionine (Met) for survival (Table 1). This evidence concerns the gene ADI1 and carcinoma.