Congenital hyperinsulinism is a condition that causes individuals to have abnormally high levels of insulin. Insulin is a hormone that helps control levels of blood glucose, also called blood sugar. People with this condition have frequent episodes of low blood glucose (hypoglycemia). In infants and young children, these episodes are characterized by a lack of energy (lethargy), irritability, or difficulty feeding. Repeated episodes of low blood glucose increase the risk for serious complications such as breathing difficulties, seizures, intellectual disability, vision loss, brain damage, and coma.

The severity of congenital hyperinsulinism varies widely among affected individuals, even among members of the same family. About 60 percent of infants with this condition experience a hypoglycemic episode within the first month of life. Other affected children develop hypoglycemia by early childhood. Unlike typical episodes of hypoglycemia, which occur most often after periods without food (fasting) or after exercising, episodes of hypoglycemia in people with congenital hyperinsulinism can also occur after eating.

Congenital hyperinsulinism is a disease where there are abnormally high levels of insulin, a hormone produced by the beta cells of the pancreas that helps control blood sugar levels. Because of the high levels of insulin, people with this disease have frequent episodes of low blood sugar (hypoglycemia) that can even occur after eating. In babies and young children, these episodes are characterized by a lack of energy (lethargy), irritability, or difficulty feeding. Repeated episodes of low blood sugar increase the risk for serious complications such as breathing difficulties, seizures, intellectual disability, vision loss, brain damage, and coma. The severity and onset of these episodes varies, even among members of the same family. In about 60% of the cases, the episodes start within the first month of life and are very severe and difficult to manage. In other cases, the disease starts in childhood or later, and the symptoms are mild. Early diagnosis and treatment is important to prevent neurologic damage from hypoglycemia.

Congenital hyperinsulinism is caused by mutations in at least 11 different genes, including ABCC8 (responsible for about 45 % of the cases), KCNJ11, GLUD1, GCK, HK1, HADH, HNF4A, HNF1A, SLC16A1, UCP2, and PGM1. Inheritance may be autosomal recessive or autosomal dominant. Some cases are caused by loss of genetic material in a region of chromosome 11 (11p15) that comes from the mother (maternal chromosome). According to the extent of abnormal beta cells, the disease can be focal (when abnormal beta cells are limited to 1 or a few areas in the pancreas) and diffuse (where the abnormal beta cells are spread throughout the pancreas). The goal of treatment is to manage the hypoglycemia to prevent brain damage. Medications may include diazoxide, octreotide, and glucagon. Surgery to remove part of the pancreas might be required in severe cases.Genetic testing may help to guide the best treatment.

Congenital hyperinsulinism is caused by mutations in genes that regulate the release (secretion) of insulin, which is produced by beta cells in the pancreas. Insulin clears excess glucose from the bloodstream by passing glucose into cells to be used as energy.

Gene mutations that cause congenital hyperinsulinism lead to over-secretion of insulin from beta cells. Normally, insulin is secreted in response to the amount of glucose in the bloodstream: when glucose levels rise, so does insulin secretion. However, in people with congenital hyperinsulinism, insulin is secreted from beta cells regardless of the amount of glucose present in the blood. This excessive secretion of insulin results in glucose being rapidly removed from the bloodstream and passed into tissues such as muscle, liver, and fat. A lack of glucose in the blood results in frequent states of hypoglycemia in people with congenital hyperinsulinism. Insufficient blood glucose also deprives the brain of its primary source of fuel.

Mutations in at least nine genes have been found to cause congenital hyperinsulinism. Mutations in the ABCC8 gene are the most common known cause of the disorder. They account for this condition in approximately 40 percent of affected individuals. Less frequently, mutations in the KCNJ11 gene have been found in people with congenital hyperinsulinism. Mutations in each of the other genes associated with this condition account for only a small percentage of cases.

In approximately half of people with congenital hyperinsulinism, the cause is unknown.

Normal Function

The ABCC8 gene provides instructions for making the sulfonylurea receptor 1 (SUR1) protein. The SUR1 protein is one part (subunit) of the ATP-sensitive potassium (K-ATP) channel that is found across cell membranes in the beta cells of the pancreas. Beta cells secrete insulin, which is a hormone that helps control blood sugar levels. Insulin controls how much sugar (in the form of glucose) is passed from the bloodstream into cells to be used as energy. The K-ATP channel controls the secretion of insulin out of beta cells and into the bloodstream. These channels open and close in response to the amount of glucose in the bloodstream, which helps regulate insulin secretion and control blood glucose levels. The closing of the channels results in a process that triggers insulin secretion by beta cells.

Health Conditions Related to Genetic Changes

Congenital hyperinsulinism

More than 300 mutations in the ABCC8 gene have been found to cause congenital hyperinsulinism. This condition causes frequent episodes of low blood glucose (hypoglycemia), decreased energy, and irritability. Most of these mutations change single protein building blocks (amino acids) in the SUR1 protein.

Some ABCC8 mutations prevent the SUR1 protein from reaching the cell membrane, interfering with the proper formation of the K-ATP channel. Other mutations interfere with the K-ATP channel's function or its responses to outside molecules. Defective K-ATP channels lead to the constant release of insulin from beta cells. As a result, glucose is rapidly removed from the bloodstream. Without treatment, the hypoglycemia caused by congenital hyperinsulinism may result in serious complications such as intellectual disability and seizures.

Permanent neonatal diabetes mellitus

At least 14 mutations in the ABCC8 gene have been identified in people with permanent neonatal diabetes mellitus. Individuals with this condition often have a low birth weight and develop increased blood sugar (hyperglycemia) within the first 6 months of life.

ABCC8 gene mutations that cause permanent neonatal diabetes mellitus change single amino acids in the protein sequence. These mutations result in K-ATP channels that do not close, leading to reduced insulin secretion from beta cells and impaired blood sugar control.

Maturity-onset diabetes of the young

MedlinePlus Genetics provides information about Maturity-onset diabetes of the young

Other disorders

Other ABCC8 gene mutations that have a relatively mild effect on K-ATP channel function as compared to that seen in permanent neonatal diabetes mellitus (see above) cause a condition called transient neonatal diabetes mellitus. Infants with this condition have hyperglycemia during the first 6 months of life, but their blood sugar returns to normal by age 18 months. However, affected individuals usually develop hyperglycemia again during adolescence or early adulthood. As in permanent neonatal diabetes mellitus, ABCC8 gene mutations that cause transient neonatal diabetes mellitus interfere with K-ATP channel closure and lead to a reduction in insulin secretion.

Some studies suggest that normal variations (polymorphisms) in the ABCC8 gene are associated with an increased risk of type 2 diabetes, the most common form of diabetes. Other studies, however, have not found an association between ABCC8 gene variants and type 2 diabetes. People with this disease have hyperglycemia because the body does not respond correctly to the insulin secreted from beta cells. Although changes in the ABCC8 gene may be associated with type 2 diabetes, a combination of lifestyle, genetic, and environmental factors all play a part in determining the risk of this complex disorder.

Other Names for This Gene

• ABC36
• ABCC8_HUMAN
• ATP-binding cassette, sub-family C (CFTR/MRP), member 8
• ATP-binding cassette, sub-family C, member 8
• MRP8
• SUR
• SUR1
• TNDM2

Genomic Location

Normal Function

The KCNJ11 gene provides instructions for making parts (subunits) of the ATP-sensitive potassium (K-ATP) channel. Each K-ATP channel consists of eight subunits. Four subunits are produced from the KCNJ11 gene, and four are produced from another gene called ABCC8.

K-ATP channels are found in beta cells, which are cells in the pancreas that secrete the hormone insulin. The K-ATP channels are embedded in cell membranes, where they open and close in response to the amount of glucose in the bloodstream. Glucose is a simple sugar and the primary energy source for most cells in the body. Closure of the K-ATP channels in response to increased glucose triggers the release of insulin out of beta cells and into the bloodstream, which helps control blood glucose levels.

Health Conditions Related to Genetic Changes

Congenital hyperinsulinism

More than 30 mutations in the KCNJ11 gene have been found to cause congenital hyperinsulinism. This condition causes frequent episodes of low blood glucose (hypoglycemia), decreased energy, and irritability. Most of these mutations change single protein building blocks (amino acids) in the protein sequence, reducing or preventing activity of the K-ATP channels. Loss of K-ATP channel function leads to the constant release of insulin from beta cells. As a result, glucose is rapidly removed from the bloodstream. Without treatment, the hypoglycemia caused by congenital hyperinsulinism may result in serious complications such as intellectual disability and seizures.

Permanent neonatal diabetes mellitus

At least 30 mutations in the KCNJ11 gene have been identified in people with permanent neonatal diabetes mellitus. Individuals with this condition often have a low birth weight and develop increased blood glucose (hyperglycemia) within the first 6 months of life.

KCNJ11 gene mutations that cause permanent neonatal diabetes mellitus change single amino acids in the protein sequence. These mutations result in K-ATP channels that do not close, leading to reduced insulin secretion from beta cells and impaired blood glucose control.

Gestational diabetes

MedlinePlus Genetics provides information about Gestational diabetes

Maturity-onset diabetes of the young

MedlinePlus Genetics provides information about Maturity-onset diabetes of the young

Other disorders

Other KCNJ11 gene mutations that have a relatively mild effect on K-ATP channel function as compared to that seen in permanent neonatal diabetes mellitus (see above) cause a condition called transient neonatal diabetes mellitus. Infants with this condition have hyperglycemia during the first 6 months of life, but their blood glucose returns to normal by age 18 months. However, affected individuals usually develop hyperglycemia again during adolescence or early adulthood. As in permanent neonatal diabetes mellitus, KCNJ11 gene mutations that cause transient neonatal diabetes mellitus also interfere with K-ATP channel closure and lead to a reduction in insulin secretion.

A normal variation (polymorphism) in the KCNJ11 gene is associated with an increased risk of type 2 diabetes, the most common form of diabetes. This variant leads to a change in the K-ATP channel, replacing the amino acid glutamic acid with the amino acid lysine at position 23, written as Glu23Lys or E23K. People with type 2 diabetes have hyperglycemia because the body does not respond correctly to the insulin secreted from beta cells. The same variant has also been associated with changes in the heart's response to stress, leading to an increased risk of heart failure. Although changes in the KCNJ11 gene can be associated with type 2 diabetes and heart failure, a combination of lifestyle, genetic, and environmental factors all play a part in determining the risk of these complex disorders.

Other Names for This Gene

• ATP-sensitive inward rectifier potassium channel 11
• beta-cell inward rectifier subunit
• BIR
• HHF2
• IKATP
• inward rectifier K(+) channel Kir6.2
• inwardly rectifying potassium channel KIR6.2
• KIR6.2
• MGC133230
• potassium channel, inwardly rectifying subfamily J member 11
• potassium channel, inwardly rectifying subfamily J, member 11
• potassium inwardly-rectifying channel, subfamily J, member 11
• TNDM3

Genomic Location

Congenital hyperinsulinism can have different inheritance patterns, usually depending on the form of the condition. At least two forms of the condition have been identified. The most common form is the diffuse form, which occurs when all of the beta cells in the pancreas secrete too much insulin. The focal form of congenital hyperinsulinism occurs when only some of the beta cells over-secrete insulin.

Most often, the diffuse form of congenital hyperinsulinism is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Less frequently, the diffuse form is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

The inheritance of the focal form of congenital hyperinsulinism is more complex. For most genes, both copies are turned on (active) in all cells, but for a small subset of genes, one of the two copies is turned off (inactive). Most people with the focal form of this condition inherit one copy of the mutated, inactive gene from their unaffected father. During embryonic development, a mutation occurs in the other, active copy of the gene. This second mutation is found within only some cells in the pancreas. As a result, some pancreatic beta cells have abnormal insulin secretion, while other beta cells function normally.

Congenital hyperinsulinism affects approximately 1 in 50,000 newborns. This condition is more common in certain populations, affecting up to 1 in 2,500 newborns.