Several factors play a causal role in this growth retardation, including small infant size at birth, metabolic acidosis, salt and water deficits, anorexia, malnutrition and cachexia, anemia, and resistance to anabolic hormones such as growth hormone (GH), insulin-like growth factor 1 (IGF1), and sexual hormones. The gene discussed is IGF1; the disease is anemia (phenotype).