PROP1 and isolated congenital growth hormone deficiency: Within the HYPOPIT study, we previously studied Dutch CPHD cases for mutations in PROP1, HESX1, POU1F1, LHX3, LHX4, OTX2, SHH and HHIP [22–24] and patients with Isolated GH Deficiency (IGHD) for GH1, GHRHR, HMGA2 and CDK6 [25–27].