IGF1 and hereditary endocrine growth disease: Severe primary IGF-I deficiency (SPIGFD) is a rare growth disorder defined by extreme short stature (height standard deviation score [HtSDS] ≤ −3), deficiency in serum levels of IGF-I (below the 2.5th percentile for age and sex in the European Union and IGF-I SD score [SDS] ≤ −3 in the United States), and normal or elevated levels of GH, indicating GH insensitivity (1).