Single gene mutations causing SGA

The growth hormone–insulin-like growth factor-I (GH–IGF-I) axis plays a key role in intra-uterine growth and development. This review will describe the consequences of genetic defects in various components of the GH–IGF-I axis on intra-uterine growth and development. Animal knockout experiments have provided evidence for the GH-independent secretion of IGF-I and its effect in utero. Reports of patients with a deletion or mutation of the IGF-I and IGF1R genes have provided insight into the role of intra-uterine IGF-I in the human. Homozygous defects of the IGF-I gene have dramatic effects on intra-uterine growth and development, whereas heterozygous defects of the IGF1R gene have a more variable clinical presentation. The phenotype in relation to the genotype of the different disorders will be reviewed in this chapter.