- Double-blind crossover study with levorotatory form of hydroxytryptophan in patients with degenerative cerebellar diseases. Wessel, K., Hermsdörfer, J., Deger, K., Herzog, T., Huss, G.P., Kömpf, D., Mai, N., Schimrigk, K., Wittkämper, A., Ziegler, W. Arch. Neurol. (1995)