What amino acid has been linked to the development of the rare blood disorder eosinophilia-myalgia syndrome in people who took it as a supplement?

Question

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Tryptophan has been linked to the development of eosinophilia-myalgia syndrome (EMS), a rare and potentially deadly blood disorder, in people who took it as a dietary supplement. The outbreak occurred in the late 1980s and early 1990s and affected thousands of people. The cause of the outbreak was traced to a contaminated batch of tryptophan produced by a Japanese manufacturer. As a result, tryptophan supplements were banned in the US and other countries, and manufacturers must now adhere to strict quality control standards to prevent contamination.

What Amino Acid Has Been Linked to the Development of the Rare