Given that glycine, D-serine, GlyT1 inhibitors, and DAAO inhibitors have all shown functional effects in rodent and human studies, as described throughout this review, these negative studies may simply result from the specific challenges that come with measuring cognition in patients with schizophrenia, in addition to typical clinical trial conduct challenges in patients with mental illness, such as ensuring medication adherence. The gene discussed is DAO; the disease is schizophrenia.