Familial hyperinsulinism is an inherited disorder that causes too much insulin to be produced. Affected individuals tend to be born large and within the first few days of life develop severe hypoglycemia (low blood sugar). Symptoms may include seizures, poor muscle tone (hypotonia), poor feeding, and apnea. If these infants do not respond completely to diet or other therapy, surgery may be done to remove part of the pancreas. Long-term monitoring and management is needed to prevent hypoglycemia, because if left untreated, irreversible brain damage will occur. One of the causes of familial hyperinsulinism is pathogenic variants in the ABCC8 gene.