Hyperinsulinaemic hypoglycaemia is a complex disorder where the pancreas produces too much insulin, causing dangerously low blood sugar levels that can lead to seizures, brain damage, and developmental problems if left untreated.
Understanding Hyperinsulinaemic Hypoglycaemia
Hyperinsulinaemic hypoglycaemia, also called HH, describes a group of conditions where the body produces excessive amounts of insulin even when blood sugar levels are already low. Normally, insulin is a hormone that helps control blood sugar by moving glucose from the bloodstream into cells where it can be used for energy. In healthy people, the pancreas carefully regulates insulin production to keep blood sugar within a normal range of 3.5 to 5.5 millimoles per liter. However, in people with hyperinsulinaemic hypoglycaemia, this regulation system breaks down, and insulin continues to be released inappropriately.[1]
This condition is particularly serious because insulin doesn’t just lower blood sugar levels. It also prevents the body from creating alternative fuel sources that the brain normally uses during periods of low glucose. Insulin blocks the breakdown of fats and the production of ketone bodies, which are substances the brain can use for energy when glucose is unavailable. Without glucose or ketones, the brain becomes starved for fuel, which is why hyperinsulinaemic hypoglycaemia poses such a significant risk for permanent brain damage.[4]
Who Is Affected and How Common Is It
Hyperinsulinaemic hypoglycaemia is the most common cause of severe and persistent low blood sugar in newborns, infants, and children. The condition can appear at birth or develop later in childhood, and in rare cases, symptoms may not appear until adulthood. The severity can range from life-threatening episodes requiring immediate medical intervention to milder cases that respond well to medication.[1]
The frequency of congenital hyperinsulinism varies significantly depending on the population. In the general population, the condition occurs in approximately one in 40,000 to 50,000 births. However, in communities where marriages between closely related family members are common, the rate can be much higher, affecting as many as one in 2,500 births. This difference exists because some forms of the condition are inherited in patterns that become more likely when both parents carry similar genetic material.[4]
While hyperinsulinaemic hypoglycaemia is most recognized in infants and children, it can also occur in adults, though the causes tend to be different. In adults, conditions such as insulinomas (insulin-producing tumors) or complications following certain types of weight-loss surgery are more common triggers.[2]
What Causes This Condition
Hyperinsulinaemic hypoglycaemia can be either congenital, meaning present from birth, or acquired later in life due to various factors. Congenital forms are primarily caused by genetic mutations that affect how pancreatic beta cells produce and release insulin. Scientists have identified mutations in at least nine different genes that can lead to this condition, though in about half of all cases, the exact genetic cause remains unknown, suggesting there are additional genes yet to be discovered.[1][4]
The most severe forms of congenital hyperinsulinism result from mutations in two specific genes: ABCC8 and KCNJ11. These genes provide instructions for making parts of the ATP-sensitive potassium channel in pancreatic beta cells, which acts like a switch to control insulin release. When these genes are mutated, the switch malfunctions, and insulin pours out continuously regardless of blood sugar levels. Other genetic forms involve mutations in genes that control glucose sensing or metabolism, such as GLUD1, GCK, HADH, HNF4A, HNF1A, SLC16A1, and UCP2.[4][8]
Acquired forms of hyperinsulinaemic hypoglycaemia have different causes. In newborns, temporary hyperinsulinism can occur due to birth complications, being born to a mother with diabetes, intrauterine growth problems, or severe infections during pregnancy. The condition can also develop in association with certain genetic syndromes like Beckwith-Wiedemann syndrome. In adults, insulin-producing tumors in the pancreas or complications from gastric bypass surgery are more typical causes.[2][4]
Risk Factors for Development
Several circumstances increase the likelihood of developing hyperinsulinaemic hypoglycaemia, particularly the transient form seen in newborns. Babies born to mothers with diabetes face increased risk because exposure to high blood sugar levels in the womb causes the baby’s pancreas to produce extra insulin. When the baby is born and no longer receives glucose through the umbilical cord, this excess insulin can cause dangerous drops in blood sugar.[3]
Other perinatal factors that elevate risk include birth asphyxia (oxygen deprivation during delivery), intrauterine growth restriction where the baby doesn’t grow properly in the womb, being born significantly larger than average for gestational age, and maternal high blood pressure during pregnancy. Babies who experience these complications need careful monitoring for signs of low blood sugar in the hours and days after birth.[3][4]
From a genetic standpoint, children born to parents who are closely related have a higher risk of inheriting the recessive forms of congenital hyperinsulinism. When both parents carry a mutation in the same gene, even if neither parent shows symptoms, their child has a one-in-four chance of inheriting both copies of the mutated gene and developing the condition. Family history of unexplained seizures in infancy, developmental delays, or diagnosed hyperinsulinism in siblings also increases risk.[4]
Recognizing the Symptoms
The symptoms of hyperinsulinaemic hypoglycaemia vary depending on the age of the person affected and how severely their blood sugar drops. In newborns and young infants, the signs can be subtle and easily missed. Affected babies may feed poorly, appearing uninterested in eating or falling asleep during feedings. They may look unusually pale, with a noticeable lack of color in their skin. Some babies develop a bluish tint around their mouth, a condition called cyanosis, which signals that their body isn’t getting enough oxygen because their brain is struggling without adequate fuel.[6]
Infants with hyperinsulinaemic hypoglycaemia may breathe faster than normal, shake or tremble, or seem weak and floppy. In severe cases, they may experience seizures, which can appear as rhythmic jerking movements, staring spells, or sudden stiffening of the body. The most dangerous consequence is loss of consciousness or coma, which represents a medical emergency. Sadly, without treatment, severe hypoglycaemia can result in death.[6]
In older children, the symptoms become more recognizable but may be confused with other conditions. These children often experience intense hunger, even shortly after eating. They may shake, sweat, or feel dizzy and lightheaded. Headaches are common, as is a rapid or pounding heartbeat. Many children become irritable, anxious, or confused when their blood sugar drops. They may have difficulty concentrating or appear unusually tired. Some children develop pale or clammy skin, and they may experience tingling sensations in their lips, tongue, or cheeks.[1][2]
When blood sugar falls to very low levels, more serious neurological symptoms emerge. These include blurred or double vision, slurred speech, and clumsiness or difficulty with coordination. Confusion deepens, and the person may become disoriented or fail to recognize familiar people or places. If untreated, severe hypoglycaemia progresses to seizures, loss of consciousness, and potentially permanent brain damage.[2]
How to Prevent Complications
Since many forms of hyperinsulinaemic hypoglycaemia are genetic and present from birth, prevention in the traditional sense isn’t always possible. However, early identification through newborn screening and prompt treatment can prevent the serious consequences of the condition. Babies at high risk, such as those born to mothers with diabetes or those who experienced complications during birth, should be monitored closely for signs of low blood sugar in the first hours and days of life.[3]
For families with a known history of congenital hyperinsulinism, genetic counseling can provide valuable information about the risk of passing the condition to future children. In some cases, genetic testing of parents or affected family members can identify specific mutations, allowing for prenatal diagnosis or early postnatal screening. This enables medical teams to be prepared with appropriate monitoring and treatment from the moment of birth.[4]
Once diagnosed, prevention focuses on avoiding episodes of low blood sugar. This requires careful attention to feeding schedules, especially in infants and young children. Frequent feedings, sometimes as often as every two to three hours including overnight, may be necessary to maintain adequate blood sugar levels. Some children require feeding through a tube that delivers a continuous supply of nutrition directly into the stomach. Families must learn to recognize early warning signs of dropping blood sugar and respond quickly with appropriate treatment.[9]
Regular monitoring of blood glucose levels becomes part of daily life for many families. This typically involves checking blood sugar before each feeding and any time symptoms appear. Maintaining blood sugar above 3.5 millimoles per liter is generally the target for children with hyperinsulinaemic hypoglycaemia. Careful record-keeping helps doctors adjust medications and feeding schedules to prevent dangerous drops while avoiding unnecessarily intensive treatment.[7]
What Happens in the Body
To understand hyperinsulinaemic hypoglycaemia, it helps to know how the body normally regulates blood sugar. After eating, carbohydrates from food are broken down into glucose, which enters the bloodstream. Rising blood sugar levels signal pancreatic beta cells to release insulin. Insulin acts like a key, unlocking cells throughout the body so glucose can enter and be used for energy. Once blood sugar drops to normal levels, insulin release decreases, preventing blood sugar from falling too low.[8]
Several backup systems protect against low blood sugar. When glucose levels begin to fall, other hormones like glucagon, cortisol, and epinephrine trigger the liver to release stored glucose and to create new glucose from other sources. These hormones also signal fat cells to break down stored fat into free fatty acids and ketone bodies, which the brain can use as alternative fuel. This complex system keeps blood sugar stable even during fasting or between meals.[4]
In hyperinsulinaemic hypoglycaemia, this finely tuned system malfunctions. Pancreatic beta cells release insulin inappropriately, without regard to blood sugar levels. The excess insulin forces glucose out of the bloodstream and into cells, causing blood sugar to plummet. At the same time, insulin blocks all the protective mechanisms that would normally prevent low blood sugar. It prevents the liver from releasing or making glucose. It stops fat breakdown, eliminating the production of free fatty acids and ketones. This leaves the brain without either of its two main fuel sources.[1][4]
The brain is particularly vulnerable in this situation. Unlike other organs, the brain cannot store glucose and depends on a constant supply from the blood. Brain cells consume glucose at a very high rate, especially in infants and young children whose brains are rapidly developing and growing. When deprived of glucose and unable to access ketones as backup fuel, brain cells begin to malfunction within minutes. Prolonged or repeated episodes of severe hypoglycaemia cause brain cells to die, leading to permanent damage in areas responsible for movement, learning, memory, and behavior.[4][5]
Different genetic mutations cause hyperinsulinaemic hypoglycaemia through various mechanisms, but all result in dysregulated insulin secretion. Mutations affecting the ATP-sensitive potassium channel prevent the normal “off switch” for insulin release. Mutations in genes controlling glucose sensing make beta cells think blood sugar is higher than it actually is, triggering inappropriate insulin release. Mutations affecting enzymes involved in processing fuels within beta cells disrupt the signals that normally match insulin release to blood sugar levels.[4][12]
The physical changes in the pancreas can vary. In diffuse hyperinsulinism, beta cells throughout the entire pancreas are affected. In focal hyperinsulinism, only a small area of the pancreas contains abnormal beta cells that produce excess insulin, while the rest of the pancreas functions normally. Understanding whether hyperinsulinaemic hypoglycaemia is diffuse or focal is crucial for treatment decisions, as focal disease can potentially be cured with surgery that removes only the affected portion of the pancreas.[1][4]
