We thank Dr Warner for drawing our attention to his earlier article.1 Of the 9 cases reported by Dr Warner in 1963, 8 were women with serum serotonin levels around 0.3 to 1.2 µg/mL (2-7 µmol/L) and 1 was a man with a serum serotonin level of 5.2 to 7.8 µg/mL (29.5-44.3 µmol/L). This sex difference and the fact that none of the patients showed normal production of urinary 5-HIAA in response to an oral serotonin load is certainly consistent with MAO deficiency. Results of urinary catecholamines and metanephrines were not reported in Dr Warner's study. No mention of a positive family history was alluded to in his very detailed description of the cases.
Cheung NW, Earl J. Monoamine Oxidase Deficiency: A Cause of Symptomatic Hyperserotoninemia in the Absence of Carcinoid—Reply. Arch Intern Med. 2002;162(14):1648. doi: