PROP1 and cyclic hematopoiesis: CH can be classified as follows: congenital IGH, defects in growth hormone (GH) production and secretion (e.g., GH1 and GHRHR), defects in pituitary cell differentiation (e.g., PROP-1 and POrU1F1), and impairment in pituitary development (e.g., HESX1, LHX3, LHX4, SOX2, SOX3, GLI2, and OTX2) (1).