MCT-1 Hyperinsulinism

What is MCT-1 hyperinsulinism?

Congenital hyperinsulinism (HI) is a genetic disorder in which the insulin cells of the pancreas, called beta cells, secrete too much insulin. Excess insulin causes low blood sugar (hypoglycemia).

Ordinarily, beta cells secrete just enough insulin to keep the blood sugar in the normal range. In children with HI, the secretion of insulin is not properly regulated, causing excess insulin secretion and low blood sugar.

MCT-1 hyperinsulinism is rare form of HI that is triggered by exercise.


MCT-1 hyperinsulinism is caused by aberrant expression of MCT (monocarboxylate transporter 1). Inheritance of the genetic defect is dominant, meaning only one parent must have a mutation of the gene to cause disease in the child.


Symptoms of MCT-1 hyperinsulinism include elevated insulin levels and hypoglycemia with anaerobic exercise.


The diagnosis of congenital hyperinsulinism is based on genetic testing and an exercise test.

Genetic testing

The DNA from a blood sample from the child with congenital HI and each parent can be analyzed to screen for the mutations that cause the most common types of HI. This can be done at commercial laboratories and should be considered in any child suspected to have congenital HI. Contact us for more information on where to have this testing performed.


MCT-1 hyperinsulinism is partially responsive to diazoxide (Proglycem).

Long-term outcomes

We are now tracking and compiling data on the long-term outlook for children with congenital HI. We know that with rapid diagnosis and appropriate treatment, keeping blood sugars >70 mg/dL, it is less likely that children with congenital HI will have long-term effects of hypoglycemia. With focal hyperinsulinism, 94 percent of children are cured with surgery.


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