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.
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Richardson M.A., Haugland G., Pass R., Craig T.J. (1986) The prevalence of tardive dyskinesia in a mentally retarded population. Psychopharmacol Bull22: 243-249
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Richardson M.A., Suckow R., Rowland Whittaker R.N., Boggiano W., Sziraki I., Kushner H., Perumal A. (1989) The plasma phenylalanine/large neutral amino acid ratio: a risk factor for tardive dyskinesia. Psychopharmacol Bull25:47-51
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