- The PROP1 2-base pair deletion is a common cause of combined pituitary hormone deficiency. Cogan, J.D., Wu, W., Phillips, J.A., Arnhold, I.J., Agapito, A., Fofanova, O.V., Osorio, M.G., Bircan, I., Moreno, A., Mendonca, B.B. J. Clin. Endocrinol. Metab. (1998)