Editing Eosinophilia–myalgia syndrome (section)

== Causes ==

Subsequent{{clarify|subsequent to what?|date=September 2024}} epidemiological studies suggested that EMS was linked to specific batches of L-tryptophan supplied by a single large Japanese manufacturer, [[Showa Denko]].<ref name="FDA_Tryptophan_Info" /><ref name="pmid2355442">{{cite journal | vauthors = Slutsker L, Hoesly FC, Miller L, Williams LP, Watson JC, Fleming DW | title = Eosinophilia-myalgia syndrome associated with exposure to tryptophan from a single manufacturer | journal = JAMA | volume = 264 | issue = 2 | pages = 213–7 | date = July 1990 | pmid = 2355442 | doi = 10.1001/jama.264.2.213 }}</ref><ref name="pmid8496862">{{cite journal | vauthors = Back EE, Henning KJ, Kallenbach LR, Brix KA, Gunn RA, Melius JM | title = Risk factors for developing eosinophilia myalgia syndrome among L-tryptophan users in New York | journal = The Journal of Rheumatology | volume = 20 | issue = 4 | pages = 666–72 | date = April 1993 | pmid = 8496862 }}</ref><ref name="pmid8895184">{{cite journal | vauthors = Kilbourne EM, Philen RM, Kamb ML, Falk H | title = Tryptophan produced by Showa Denko and epidemic eosinophilia-myalgia syndrome | journal = The Journal of Rheumatology. Supplement | volume = 46 | pages = 81–8; discussion 89–91 | date = October 1996 | pmid = 8895184 }}</ref> It eventually became clear that recent batches of Showa Denko's L-tryptophan were contaminated by trace impurities, which were subsequently thought to be responsible for the 1989 EMS outbreak. The L-tryptophan was produced by a bacterium grown in open vats in a Showa Denko fertilizer factory.<ref name="FDA_Tryptophan_Info" /><ref name="pmid2270484">{{cite journal | vauthors = Mayeno AN, Lin F, Foote CS, Loegering DA, Ames MM, Hedberg CW, Gleich GJ | title = Characterization of "peak E," a novel amino acid associated with eosinophilia-myalgia syndrome | journal = Science | volume = 250 | issue = 4988 | pages = 1707–8 | date = December 1990 | pmid = 2270484 | doi = 10.1126/science.2270484 | bibcode = 1990Sci...250.1707M }}</ref><ref name="pmid1544609">{{cite journal | vauthors = Ito J, Hosaki Y, Torigoe Y, Sakimoto K | title = Identification of substances formed by decomposition of peak E substance in tryptophan | journal = Food and Chemical Toxicology | volume = 30 | issue = 1 | pages = 71–81 | date = January 1992 | pmid = 1544609 | doi = 10.1016/0278-6915(92)90139-C }}</ref> While a total of 63 trace contaminants were eventually identified, only six of them could be associated with EMS.<ref name="pmid7765187" /><ref name="pmid8346973">{{cite journal | vauthors = Hill RH, Caudill SP, Philen RM, Bailey SL, Flanders WD, Driskell WJ, Kamb ML, Needham LL, Sampson EJ | display-authors = 6 | title = Contaminants in L-tryptophan associated with eosinophilia myalgia syndrome | journal = Archives of Environmental Contamination and Toxicology | volume = 25 | issue = 1 | pages = 134–42 | date = July 1993 | pmid = 8346973 | doi = 10.1007/bf00230724 | bibcode = 1993ArECT..25..134H | s2cid = 10182128 }}</ref> The compound EBT (1,1'-ethylidene-bis-L-tryptophan, also known as "Peak E") was the only contaminant identifiable by initial analysis, but further analysis revealed PAA (3-(phenylamino)-L-alanine, also known as "UV-5"), and peak 200 (2[3-indolyl-methyl]-L-tryptophan). Two of the remaining uncharacterized peaks associated with EMS were later determined to be 3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo-[2,3-b]-indole-2-carboxylic acid (peak C) and 2-(2-hydroxy indoline)-tryptophan (peak FF). These were characterized using accurate mass [[Liquid chromatography–mass spectrometry|LC–MS, LC–MS/MS]] and multistage mass spectrometry (MS<sup>n</sup>).<ref name="Williamson1998">{{cite journal | vauthors = Williamson BL, Johnson KL, Tomlinson AJ, Gleich GJ, Naylor S | title = On-line HPLC-tandem mass spectrometry structural characterization of case-associated contaminants of L-tryptophan implicated with the onset of eosinophilia myalgia syndrome | journal = Toxicology Letters | volume = 99 | issue = 2 | pages = 139–50 | date = October 1998 | pmid = 9817085 | doi = 10.1016/S0378-4274(98)00223-9 }}</ref> The last of the six contaminants (peak AAA/"UV-28",<ref name="Allen2014">{{cite journal | vauthors = Allen JA, Varga J | title=Eosinophilia–Myalgia Syndrome |journal=Encyclopedia of Toxicology (Third Edition) |date=1 January 2014 |pages=419–425 |doi=10.1016/b978-0-12-386454-3.00018-x |publisher=Academic Press |isbn=9780123864550 }}</ref> being "the contaminant most significantly associated with EMS" <ref name="pmid7765187" /> has been characterized as two [[Structural isomer|related chain-isomers]]; peak AAA<sub>1</sub> ((S)-2-amino-3-(2-((S,E)-7-methylnon-1-en-1-yl)-1H-indol-3-yl)propanoic acid, a [[Condensation reaction|condensation product]] between L-tryptophan and 7-methylnonanoic acid) and peak AAA<sub>2</sub> ((S)-2-amino-3-(2-((E)-dec-1-en-1-yl)-1H-indol-3-yl)propanoic acid, a condensate between L-tryptophan and decanoic acid).<ref name="Klarskov2018">{{cite journal | vauthors = Klarskov K, Gagnon H, Boudreault PL, Normandin C, Plancq B, Marsault E, Gleich GJ, Naylor S | display-authors = 6 | title = Structure determination of disease associated peak AAA from l-Tryptophan implicated in the eosinophilia-myalgia syndrome | journal = Toxicology Letters | volume = 282 | pages = 71–80 | date = January 2018 | pmid = 29037509 | doi = 10.1016/j.toxlet.2017.10.012 }}</ref> No consistent relationship has ever been firmly established between any specific trace impurity or impurities identified in these batches and the effects of EMS. While EBT in particular has been frequently implicated as the culprit, there is no statistically significant association between EBT levels and EMS.<ref name="pmid7765187" /> Of the 63 trace contaminants, only the two AAA compounds displayed a statistically significant association with cases of EMS (with a [[p-value]] of 0.0014).<ref name="Klarskov2018" />

As most research has focused on attempts to associate individual contaminants with EMS, there is a comparative lack of detailed research on other possible causal or contributing factors. Tryptophan itself has been implicated as a potentially major contributory factor in EMS.<ref name="pmid16307217">{{cite journal | vauthors = Smith MJ, Garrett RH | title = A heretofore undisclosed crux of eosinophilia-myalgia syndrome: compromised histamine degradation | journal = Inflammation Research | volume = 54 | issue = 11 | pages = 435–50 | date = November 2005 | pmid = 16307217 | doi = 10.1007/s00011-005-1380-7 | s2cid = 7785345 }}</ref> While critics of this theory have argued that this hypothesis fails to explain the near-absent reports of EMS prior to and following the EMS outbreak,<ref name="Fernstrom2012">{{cite journal | vauthors = Fernstrom JD | title = Effects and side effects associated with the non-nutritional use of tryptophan by humans | journal = The Journal of Nutrition | volume = 142 | issue = 12 | pages = 2236S–2244S | date = December 2012 | pmid = 23077193 | doi = 10.3945/jn.111.157065 | doi-access = free }} — '''''Important''': While this article may appear to be a normal peer-reviewed scientific publication at first glance, it is in fact actually a [[Supplement (publishing)|paid supplement]] (sponsored content, which is a form of [[native advertising]]) that did not go through the normal peer review process (or even the normal editorial process) for The Journal of Nutrition. It is legally required to be marked as a paid advertisement (a fact that was buried in a long footnote on the first page of the article rather than being clearly highlighted anywhere). Its sole author also disclosed a major conflict of interest due to them being "an occasional scientific advisor to the Ajinomoto Company" (the Ajinomoto Company specializes in producing animo acids, including tryptophan), and was sponsored by the International Council on Amino Acid Science (ICAAS), a non-profit association established for/by amino acids producers and users with a membership consisting exclusively of corporations with major financial conflicts of interest in the area, at least half of which are corporations which actually currently manufacture tryptophan (such as and including the Ajinomoto Company). This reference should not be considered a reliable source for anything beyond the sole claim it is used to support ("critics of this theory have argued that this hypothesis fails to explain the near-absent reports of EMS prior to and following the EMS outbreak"), and it is only used as the supporting reference for that claim in the first place because no higher-quality alternative to it currently exists.''</ref> this fails to take into account the sudden rapid increase in tryptophan's usage immediately prior to the 1989 outbreak, and ignores the strong influence of the EMS outbreak's legacy and the extended FDA ban on later usage of tryptophan.<ref name="pmid16307217" /> Crucially, this also ignores the existence of a number of cases of EMS that developed both prior to and after the primary epidemic, including at least one case where the tryptophan was tested and found to lack the contaminants found in the contaminated lots of Showa Denko's tryptophan, as well as cases with other supplements inducing EMS, and even a case of EMS induced by excessive dietary L-tryptophan intake via overconsumption of cashew nuts.<ref name="pmid2391954" /><ref name="pmid1863073" /><ref name="pmid3336240" /><ref name="pmid2222105" /><ref name="FDA_Tryptophan_Info" /><ref name="pmid16307217" /><ref name="Allen2011">{{cite journal | vauthors = Allen JA, Peterson A, Sufit R, Hinchcliff ME, Mahoney JM, Wood TA, Miller FW, Whitfield ML, Varga J | display-authors = 6 | title = Post-epidemic eosinophilia-myalgia syndrome associated with L-tryptophan | journal = Arthritis and Rheumatism | volume = 63 | issue = 11 | pages = 3633–9 | date = November 2011 | pmid = 21702023 | pmc = 3848710 | doi = 10.1002/art.30514 }}</ref><ref>{{cite journal | last1 = Barešić | first1 = Marko | last2 = Bosnić | first2 = Dubravka | last3 = Bakula | first3 = Marija | last4 = Žarković | first4 = Kamelija | name-list-style = vanc | title = Eosinophilia-myalgia syndrome induced by excessive L-tryptophan intake from cashew nuts | journal = Open Medicine | date = 1 January 2014 | volume = 9 | issue = 6 | pages = 796–801 | doi = 10.2478/s11536-013-0339-2| pmid = 32288933 | pmc=7102313 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Grangeia T, Schweller M, Paschoal IA, Zambon L, Pereira MC | title = [Acute respiratory failure as a manifestation of eosinophilia-myalgia syndrome associated with L-tryptophan intake] | language = pt | journal = Jornal Brasileiro de Pneumologia | volume = 33 | issue = 6 | pages = 747–51 | date = December 2007 | pmid = 18200378 | doi = 10.1590/S1806-37132007000600021 | trans-title = Acute respiratory failure as a manifestation of eosinophilia - myalgia syndrome associated with L- tryptophan intake | doi-access = free }}</ref>{{excessive citations inline|date=July 2022}} A major Canadian analysis located a number of patients that met the CDC criteria for EMS but had never been exposed to tryptophan, which "brings causal interpretations of earlier studies into question".<ref name="pmid8895183" /><ref name="pmid7728400">{{cite journal | vauthors = Spitzer WO, Haggerty JL, Berkson L, Davis W, Palmer W, Tamblyn R, Laprise R, Faith JM, Elmore JG, Horwitz RI | display-authors = 6 | title = Continuing occurrence of eosinophilia myalgia syndrome in Canada | journal = British Journal of Rheumatology | volume = 34 | issue = 3 | pages = 246–51 | date = March 1995 | pmid = 7728400 | doi = 10.1093/rheumatology/34.3.246 }}</ref> Other studies have highlighted numerous major flaws in many of the epidemiological studies on the association of tryptophan with EMS, which cast serious doubt on the validity of their results.<ref name="pmid8543957">{{cite journal | vauthors = Daniels SR, Hudson JI, Horwitz RI | title = Epidemiology of potential association between L-tryptophan ingestion and eosinophilia-myalgia syndrome | journal = Journal of Clinical Epidemiology | volume = 48 | issue = 12 | pages = 1413–27; discussion 1429–40 | date = December 1995 | pmid = 8543957 | doi = 10.1016/0895-4356(95)00503-x | doi-access = free }}</ref><ref name="pmid8895181">{{cite journal | vauthors = Shapiro S | title = Epidemiologic studies of the association of L-tryptophan with the eosinophilia-myalgia syndrome: a critique | journal = The Journal of Rheumatology. Supplement | volume = 46 | pages = 44–58; discussion 58–9 | date = October 1996 | pmid = 8895181 }}</ref> As the FDA concluded, "other brands of L-tryptophan, or L-tryptophan itself, regardless of the levels or presence of impurities, could not be eliminated as causal or contributing to the development of EMS".<ref name="FDA_Tryptophan_Info" /> Even animal studies have suggested that tryptophan itself "when ingested by susceptible individuals either alone or in combination with some other component in the product, results in the pathological features in EMS".<ref name="FDA_Tryptophan_Info" /><ref name="pmid10721094">{{cite book | vauthors = Gross B, Ronen N, Honigman S, Livne E | title = Tryptophan, Serotonin, and Melatonin | chapter = Tryptophan Toxicity—Time and Dose Response in Rats | series = Advances in Experimental Medicine and Biology | volume = 467 | pages = 507–16 | date = 1999 | pmid = 10721094 | doi = 10.1007/978-1-4615-4709-9_63 | isbn = 978-1-4613-7133-5 }}</ref>

At the time of the outbreak, Showa Denko had recently made alterations to its manufacturing procedures that were thought to be linked to the possible origin of the contaminants detected in the affected lots of tryptophan. A key change was the reduction of the amount of activated charcoal used to purify each batch from >20&nbsp;kg to 10&nbsp;kg.<ref name="pmid7765187" /> A portion of the contaminated batches had also bypassed another filtration step that used reverse-osmosis to remove certain impurities.<ref name="pmid7765187" /> Additionally, the bacterial culture used to synthesize tryptophan was a strain of ''[[Bacillus amyloliquefaciens]]'' that had been [[genetic engineering|genetically engineered]] to increase tryptophan production. Although the prior four generations of the genetically engineered strain had been used without incident, the fifth generation used for the contaminated batches was thought to be a possible source of the impurities that were detected. This has been used to argue that the genetic engineering itself was the primary cause of the contamination, a stance that was heavily criticized for overlooking the other known non-GMO causes of contamination, as well as for its use by anti-GMO activists as a way to threaten the development of biotechnology with false information.<ref name="Science2000">{{cite journal | vauthors = Raphals P | title = Does medical mystery threaten biotech? | journal = Science | volume = 250 | issue = 4981 | pages = 619 | date = November 1990 | pmid = 2237411 | doi = 10.1126/science.2237411 | bibcode = 1990Sci...250..619R }}</ref> The reduction in the amount of [[activated carbon]] used and the introduction of the fifth generation ''Bacillus amyloliquefaciens'' strain were both associated with the development of EMS, but due to the high overlap of these changes, the precise independent contribution of each change could not be determined (although the bypass of the reverse-osmosis filtration for certain lots was determined to be not significantly associated with the contaminated lots of tryptophan).<ref name="pmid7765187">{{cite journal | vauthors = Mayeno AN, Gleich GJ | title = Eosinophilia-myalgia syndrome and tryptophan production: a cautionary tale | journal = Trends in Biotechnology | volume = 12 | issue = 9 | pages = 346–52 | date = September 1994 | pmid = 7765187 | doi = 10.1016/0167-7799(94)90035-3 }}</ref> While Showa Denko claimed a purity of 99.6%, it was noted that "the quantities of the known EMS associated contaminants, EBT and PAA, were remarkably small, of the order of 0.01%, and could easily escape detection".<ref name="pmid7765187" />

=== Regulatory response ===
The FDA loosened its restrictions on sales and marketing of tryptophan in February 2001,<ref name="FDA_Tryptophan_Info" /> but continued to limit the importation of tryptophan not intended for an exempted use until 2005.<ref name="Allen2011"/>