Bimodal distribution of serum tryptophan level

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Abstract
Serum levels of total L-tryptophan (L-TP) were determined before and during treatment in patients suffering from endogenous depression, who were treated with L-TP, 6 g daily, and unilateral electroconvulsive therapy (ECT). The Gaussian curve of initial L-TP concentrations changed into a bimodal distribution during treatment. The patients with initially lower L-TP levels had lower L-TP levels during treatment, forming the low-concentration group within the bimodal distribution. In the patients with higher initial concentrations, the L-TP levels increased to a much greater degree, forming the high-concentration group. Patients in this group needed a larger number of ECT, probably owing to L-TP property of shortening the seizure duration. No other background data or clinical variables showed significant differences between the groups. The bimodality of L-TP levels may be genetically determined.