GH1 and isolated congenital growth hormone deficiency: These conditions result from: (i) a GH releasing hormone-receptor (GHRH-R) defect; (ii) GH gene deletion (isolated GH deficiency, IGHD); (iii) GH receptor (GHR) gene deletion or mutation (Laron syndrome); (iv) IGF1 gene deletion or IGF1R gene defect.