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Diseases

familial hyperinsulinism, ABCC8-related

What is Familial Hyperinsulinism, ABCC8-related?

Familial hyperinsulinism, ABCC8-related is an inherited condition that causes low blood sugar levels (hypoglycemia). In a healthy individual, the pancreas secretes a hormone called insulin after eating carbohydrates in response to rising blood sugar. In familial hyperinsulinism, insulin is secreted even without carbohydrate consumption. An excess of insulin released into the blood can cause blood sugars to drop to dangerously low levels. Familial hyperinsulinism, ABCC8-related is caused by harmful genetic changes (mutations) in the ABCC8 gene.

Infants with familial hyperinsulinism tend to have very low blood sugar within the first few days of life. These newborns are typically larger at birth and may have difficulty feeding, poor muscle tone, and breathing problems. These infants often require immediate infusions of glucose to help raise blood sugar levels and prevent seizures. Prolonged hypoglycemia can also lead to permanent brain damage. In some individuals with familial hyperinsulinism, symptoms do not appear until later in childhood. The low blood sugar associated with the condition can also range from mild to severe depending on the individual, and it can vary even among members of the same family.

There are two forms of familial hyperinsulism: the diffuse form and the focal form, each inherited in a different manner.

Diffuse form

In the diffuse form of the disease, all insulin-producing cells in the pancreas are affected. The diffuse form is typically inherited in an autosomal-recessive manner (i.e., two mutations are needed to cause the condition). In approximately 10 to 20% of cases, it is inherited an autosomal-dominant manner (i.e., only one mutation is needed to cause the condition), in which case carriers may be at risk for symptoms of hyperinsulism.

Focal form

In the focal form of the disease, only some of the insulin-producing cells of the pancreas are affected. For a child to have this form of the disease, two separate events must occur. The first is the inheritance of an ABCC8 mutation from their father. The second is that during fetal development a spontaneous mutation must arise in their other copy of the ABCC8 gene. This spontaneous mutation will only occur in some of the cells, which explains the focal nature. Male carriers have a 1 in 1,200 risk of having a child affected with focal hyperinsulism.

Additional findings

Specific mutations in the ABCC8 gene cause neonatal diabetes. In neonatal diabetes, not enough insulin is secreted, and blood sugar increases to dangerously high levels (hyperglycemia). Infants with neonatal diabetes tend to have high blood sugar levels between birth and six months of age. These newborns are typically smaller at birth and may have difficulty feeding, severe dehydration, glucose in the urine, and excessive urination. While some with neonatal diabetes need lifelong treatment to prevent high blood sugar, others may not experience symptoms after a few weeks or months. In rare cases, some infants may also have neurological symptoms, which can include developmental delay, muscle weakness, and seizures. As in familial hyperinsulinism, symptoms of neonatal diabetes can range from mild to severe, and severity can vary among family members. In most cases, neonatal diabetes caused by ABCC8 is inherited in an autosomal-dominant manner. Carriers may be at risk for diabetes.

How common is Familial Hyperinsulinism, ABCC8-related?

Several genes are known to cause familial hyperinsulinism, with ABCC8 mutations accounting for approximately 45% of documented cases. The overall incidence of hyperinsulinism is approximately 1 in 50,000 individuals. The incidence of familial hyperinsulinism, ABCC8-related may be more common among individuals of Ashkenazi Jewish descent.

How is Familial Hyperinsulinism, ABCC8-related treated?

Treatment for familial hyperinsulinism includes a special diet, medications, and surgical intervention. If an infant shows symptoms of familial hyperinsulinism at birth, glucose is often given through a vein (intravenously) to raise and stabilize the blood sugar level. Infants may also need frequent feedings with large amounts of carbohydrates, even overnight. A feeding tube may be helpful to ensure that an infant receives sufficient quantities of carbohydrates.

There are also several types of medications that manage familial hyperinsulinism. Most of these medications focus on reducing the amount of insulin that is released into the body. Surgery may be needed to remove part of the pancreas if diet and medication cannot sufficiently manage a patient's blood sugar levels.

After an extended period of successful treatment, many with familial hyperinsulinism find that their symptoms become less severe or even go into remission. However, individuals with familial hyperinsulinism may find their symptoms get worse if they have a viral infections. Such individuals should manage their symptoms carefully if they become ill, even if their symptoms have gone into remission. They should also avoid long periods of time without eating.

What is the prognosis for an individual with Familial Hyperinsulinism, ABCC8-related?

The long-term outlook for an individual with familial hyperinsulinism depends upon the severity of the symptoms and how well individuals respond to treatment. Permanent brain damage can occur from episodes of low blood sugar. Even with treatment, those with the disease can develop some degree of brain damage or have learning difficulties. They also may be at an elevated risk of diabetes. In the most serious cases, when the disease is not recognized and properly treated, it can be fatal. With early diagnosis and careful treatment, individuals with familial hyperinsulinism can have normal lifespans.