Prior studies in mice genetically deficient in the IDO enzyme (the enzyme expressed by the placenta that is responsible for the conversion of l-tryptophan into l-kynurenine) suggest that blocking l-tryptophan conversion into l-kynurenine in the placenta could lead to impaired placentation and pregnancy complications such as preeclampsia (30). The gene discussed is IDO1; the disease is preeclampsia.