Schizophrenia, rheumatoid arthritis and trytophan metabolism

Rheumatoid arthritis and schizophrenia have been described in early surveys as mutually exclusive disorders. Such claims are seen as especially interesting in view of: (1) indications that both illnesses often follow prodromes of severe psychological stress, (2) theories regarding hypermethylation of indoleamines producing endogenous psychotogens in schizophrenia, and (3) studies of rheumatoid arthritis reporting excessive binding of L-tryptophan to plasma protein, abnormalities of urinary tryptophan metabolites, decreased serotonin binding capacity of thrombocytes, and decreased MAO activity in joint fluid. Further comparative studies of tryptophan metabolism in schizophrenia and rheumatoid arthritis might enhance knowledge of pathogenesis in either or both diseases.