PROP1 and pituitary stalk interruption syndrome: Pituitary stalk interruption syndrome is a rare developmental pituitary defect, and germline homozygous mutations in certain transcription factors including HESX1, LHX4, OTX2, SOX3, TGIF and PROP1 have been identified as the collective drivers for familial PSIS in several case reports 9, 13, 17, 19, 20, 21, 22, 23.