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The ratio of the plasma concentration of phenylalanine (PA) to the sum of the plasma concentrations of other large neutral amino acids (LNAA) was calculated in 26 chronic, in-patient schizophrenics who met diagnostic criteria for tardive dyskinesia and 22 patients who did not. No difference in the PA/LNAA ratio was found between the two groups. Small positive correlations were found between age and both PA/LNAA ratio and tardive dyskinesia. Neuroleptic dose correlated negatively with both age and plasma PA/LNAA ratio. No support was found for previous reports of increased plasma PA/LNAA ratio in schizophrenic patients with tardive dyskinesia.

Original publication




Journal article


J Psychopharmacol

Publication Date





278 - 280