Eosinophilia-myalgia syndrome is an incurable and sometimes fatal flu-like neurological condition that was caused by contaminated L-tryptophan supplements. Similar to regular eosinophilia, it causes an increase in eosinophil granulocytes in the patient's blood. more...
In 1989 an outbreak of eosinophilia-myalgia syndrome was traced to an improperly prepared batch of tryptophan. The bacterial culture used to synthesise tryptophan had recently been genetically engineered to increase tryptophan production: unfortunately, with the higher tryptophan concentration in the culture medium, the purification process had also been modified to reduce costs, and a purification step that used charcoal absorption to remove impurities had been modified so that reduced amounts of charcoal were used. It is possible that one or more of these modifications allowed new or greater impurities through the purification. The specific impurity (or impurities) responsible for the toxic effects is still equivocal, although several impurities have been associated with the disease, and their chemical structures determined. Regardless of the origin of the toxicity, tryptophan was banned from sale in the US, and other countries followed suit. In February 2001, the FDA loosened the restrictions on the marketing of tryptophan (though not on importation).
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