Congenital hyperinsulinism (HI) is the most frequent cause of severe, persistent hypoglycemia in newborn babies and children. In most countries it occurs in approximately 1/25,000 to 1/50,000 births. About 60% of babies with HI are diagnosed during the first month of life. An additional 30% will be diagnosed later in the first year and the remainder after that. With early treatment and aggressive prevention of hypoglycemia, brain damage can be prevented. However, brain damage can occur in children with HI if the condition is not recognized or if treatment is ineffective in the prevention of hypoglycemia.
Insulin is the most important hormone for controlling the concentration of glucose in the blood. As food is eaten, blood glucose rises and the pancreas secretes insulin to keep blood glucose in the normal range. Insulin acts by driving glucose into the cells of the body. This action of insulin maintains blood glucose levels and stores glucose as glycogen in the liver. Once feeding is completed and glucose levels fall, insulin secretion is turned off, allowing the stores of glucose in glycogen to be released into the bloodstream to keep blood glucose normal. In addition, with the switching off of insulin secretion, protein and fat stores become accessible and can be used instead of glucose as sources of fuel. In this manner, whether one eats or is fasting blood glucose levels remain in the normal range and the body has access to energy at all times.
This close regulation of blood glucose and insulin secretion does not occur normally in people who have HI. The beta cells in the pancreas, which are responsible for insulin secretion, are blind to the blood glucose level and secrete insulin regardless of the blood glucose concentration. As a result, the baby or child with HI can develop hypoglycemia at any time but particularly when fasting. In the most severe form of HI this glucose blindness causes frequent, random episodes of hypoglycemia.
HI causes a particularly damaging form of hypoglycemia because it denies the brain of all the fuels on which it is critically dependent. These fuels are glucose, ketones, and lactate. The usual protective measures against hypoglycemia, such as conversion of protein to glucose (called gluconeogenesis) and conversion of fat into ketones (called fatty acid oxidation and ketogenesis) are prevented by insulin. Once the brain cells are deprived of these important fuels, they cannot make the energy they need to work and so they stop working. The lack of appropriate fuel to the brain may result in seizures and coma and if prolonged may result in death of the cells. It is this cell damage which can manifest as a permanent seizure disorder, learning disabilities, cerebral palsy, blindness or even death.