The GH1 gene is located on chromosome 17q22.24, and its mutations are responsible for several distinct forms of IGHD, including IGHD type IA, IGHD type IB (also associated with GHRHR mutations), IGHD type II, and Kowarski syndrome (also known as “bioinactive GH syndrome”). Here, GHRHR is linked to isolated congenital growth hormone deficiency.