- Specific genetic deficiencies of the A and B isoenzymes of monoamine oxidase are characterized by distinct neurochemical and clinical phenotypes. Lenders, J.W., Eisenhofer, G., Abeling, N.G., Berger, W., Murphy, D.L., Konings, C.H., Wagemakers, L.M., Kopin, I.J., Karoum, F., van Gennip, A.H., Brunner, H.G. J. Clin. Invest. (1996)