Showa Denko
In the 1980s Showa Denko applied genetic engineering to the bacteria it used in the fermentation through which it manufactured tryptophan so that the bacteria would be more efficient. At the same time, they also changed the technique used to purify the tryptophan. Some epidemiological studies traced an outbreak of eosinophilia-myalgia syndrome (EMS) to L-tryptophan supplied by Showa Denko. It was further hypothesized that one or more trace impurities produced during the manufacture of tryptophan may have been responsible for the EMS outbreak. The fact that the Showa Denko facility used genetically engineered bacteria to produce L-tryptophan gave rise to speculation that genetic engineering was responsible for such impurities. However, the methodology used in the initial epidemiological studies has been criticized. An alternative explanation for the 1989 EMS outbreak is that large doses of tryptophan produce metabolites which inhibit the normal degradation of histamine and excess histamine in turn has been proposed to cause EMS. Once the link between EMS and Showa Denko's tryptophan had been established, chemical analyses of the tryptophan was performed by researchers at the Mayo Clinic, the U.S. Food and Drug Administration (FDA), the Centers for Disease Control (CDC) and the Japanese National Institute of Hygienic Sciences to determine if any contaminants were associated with EMS. Showa Denko reportedly destroyed the GM bacterial stocks after the EMS cases began to emerge. In 2017, the last of the 6 contaminant associated with the 1989 EMS disease outbreak, labelled "Peak AAA", has been identified using high-resolution mass spectroscopy.