GHR and Laron syndrome: Classical GHI, such as Laron syndrome, results from biallelic mutations in the GH receptor (GHR) gene and is characterized by severe postnatal growth retardation, midfacial hypoplasia, delayed puberty, and extremely low serum levels of IGF-I, IGFBP-3, and acid-labile subunit that fail to respond to GH stimulation [42,43].