Spectrum of insulin-like growth factor deficiency.

There are eight known genetic causes of short stature characterized by low serum IGF-1 (IGF-1 deficiency, IGFD) and normal GH secretion. One of these (GHSR defect) is a form of secondary IGFD, although the GH peak in provocation tests can be normal. Bioinactive GH (GH1 mutations) can disturb GH secretion, but also GH binding and signaling. The remaining conditions are classified as primary IGFD (GH insensitivity). The clinical phenotype of GH receptor (GHR) defects is variable. Of the three GH signal transduction defects, a STAT5B defect is well established, but abnormalities in the MAPK pathway (such as PTPN11 mutations in Noonan syndrome) and NF-ĸB pathway (IĸBα mutation) may also cause IGFD. Homozygous IGFALS defects are relatively common, and lead to moderate growth failure, very low serum IGF-1 and even lower IGFBP-3, while a heterozygous IGFALS mutation decreases height by 1 SD. Most cases with a homozygous IGF1 defect are very short, microcephalic, and deaf, but heterozygous mutations may also lead to short stature. IGFD can also have a digenic or oligogenic origin. The diagnostic yield of genetic testing in children with a height <-2.5 SDS and a serum IGF-1 <-2 appears sufficient to perform genetic tests for known candidate genes.