- Effect of L-dopa on pattern visual evoked potentials (P-100) and neuropsychological tests in untreated adult patients with phenylketonuria. Ullrich, K., Weglage, J., Oberwittler, C., Pietsch, M., Fünders, B., van Eckhardstein, H., Colombo, J.P. J. Inherit. Metab. Dis. (1994)