The association between risk factors for tardive dyskinesia and phenylalanine-induced abnormal movements in schizophrenia

We examined whether an oral challenge dose of the amino acid phenylalanine (a dopamine precursor) exacerbates the abnormal movements of tardive dyskin esia (TD). We also examined age, gender, treatment duration, and baseline m ovement severity in relation to phenylalanine-induced changes in movements. Lastly, we assessed the influence of fasting amino acid levels on phenylal anine-induced movements, In a placebo-controlled fashion, the abnormal invo luntary movement scale (AIMS) was obtained on 25 patients before and after a phenylalanine challenge drink. A general linear model determined the rela tive effects of age, gender, treatment duration, and fasting amino acid lev els on the magnitude of induced movements. Age and treatment duration did n ot affect phenylalanine-induced movements. Lower fasting levels of phenylal anine were associated with greater movements after controlling for age, F = 11.89, p < 0.003. The severity of abnormal movements at baseline also pred icted response to phenylalanine, F = 8.62, p = 0.0079. Brain amino acid and neurotransmitter pools are influenced by changes in dietary protein, which may have implications in the development and prevention of movement disord ers. This study suggests that fasting amino acid levels may predict differe nces in vulnerability to movements during an influx of neurotransmitter pre cursors, perhaps due to long-term compensatory changes in receptor sensitiv ity. Copyright (C) 2001 John Wiley & Sons, Ltd.