is an inherited condition that causes individuals to have abnormally high levels of insulin, which leads to frequent episodes of low blood sugar (hypoglycemia). In infants and young children, these episodes are characterized by a lack of energy (lethargy), irritability, and/or difficulty feeding. Repeated episodes of low blood sugar increase the risk for serious complications such as seizures, intellectual disability, breathing difficulties, and/or coma. Unlike typical episodes of hypoglycemia, which occur after periods without food (fasting), episodes of hypoglycemia in people with familial hyperinsulinism can also occur after eating or exercising. Mutations in at least seven genes have been found to cause this condition. It is often inherited in an autosomal recessive pattern or less commonly, an autosomal dominant pattern. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.