Prop1 encodes a paired-like homeodomain transcription factor, and is a heritable responsive gene for the combined pituitary hormone deficiency in the Ames dwarf mice (Prop1-deficient dwarf mice) (15) and human patients showing absence or low levels of GH, PRL, TSH, LH and FSH (16–18), as well as ACTH (19). This evidence concerns the gene PROP1 and hypopituitarism.