The ratio of plasma phenylalanine to other large neutral amino acids is not a risk factor for tardive dyskinesia.
Geddes J., Reynolds G., Rattenbury JM., Peet M.
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.