Polymorphisms in the IGFI and IGFIR genes and children born small for gestational age:: results of large population studies

Small for gestational age (SGA) is the term used to describe a group of children born with a birth weight and/or birth length below the normal range of a reference population, corrected for their gestational age. Although animal models have shown that insulin-like growth factor I (IGFI) and insulin-like growth factor I receptor (IGFIR) genes are important candidates for reduced pre-and postnatal growth, only limited case reports have been published describing mutations. This might suggest that IGFI and IGFIR are such crucial growth factors that only common genetic polymorphisms are allowed to survive. Common IGFI and IGFIR gene polymorphisms, such as single nucleotide polymorphisms and variable number of tandem repeats, have been investigated with conflicting results with respect to SGA-related outcomes. The exact contribution of these polymorphisms to clinical practice remains to be elucidated.