Glucokinase Congenital Hyperinsulinism
What is glucokinase congenital 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.
In glucokinase HI, all beta cells in the pancreas are affected. The beta cells are not able to turn off insulin secretion when the blood glucose is too low.
Glucokinase HI is caused by a defective glucokinase gene, which serves as the thermostat for the beta cell in the pancreas, turning insulin secretion on and off.
This form of HI has a dominant inheritance pattern, meaning a child can develop the disease if just one of his parents has an abnormal glucokinase gene.
Congenital hyperinsulinism causes low blood sugar (hypoglycemia).The symptoms of hypoglycemia in infants are often difficult to identify, as they can be similar to normal infant activities.
Common symptoms of hypoglycemia include:
- excessive hunger
- rapid heart rate
More severe symptoms, such as seizures and coma, can occur with a prolonged low blood sugar or an extremely low blood sugar. Common symptoms of hypoglycemia in older children include feelings of shakiness, weakness, tiredness, confusion, and rapid heart rate.
We consider a normal blood sugar to be >70 mg/dL. Anything less than 60 mg/dL is low, although severe symptoms due to hypoglycemia are not likely unless the blood sugar is less than 50 mg/dL. Prolonged or severe low blood sugar can cause seizures and permanent brain damage.
The diagnosis of congenital hyperinsulinism is based on history, laboratory findings, and genetic testing. Prompt diagnosis and establishment of effective treatment are essential to avoid neurologic damage. The diagnosis is made by evaluating the child's medical history, and the result of laboratory and genetic tests.
The history of the child is an important piece of the puzzle. This includes information such as when the low blood sugars started, the timing of the low blood sugars, whether the baby was born large for gestational age (LGA), any family history of low blood sugar or unexplained infant deaths.
Blood tests drawn when the blood sugar is less than 50 mg/dL are essential to the diagnosis of HI. In congenital HI, with a blood sugar <50, you will see suppressed ketones and free fatty acids, an elevated insulin level (although this may not always be captured), and a glycemic response to glucagon, with the blood sugar rising more than 30 mg/dL when glucagon is administered.
It is important that these samples at the time of a critically low blood sugar be obtained in an experienced, controlled environment, as we do not want a child to be kept with a critically low blood sugar longer than is absolutely necessary to make the diagnosis.
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.
Less than 1/3 of reported cases of glucokinase HI respond well to medical therapy with diazoxide (Proglycem). Children with this form of HI may require additional support, such as dextrose administered via gastrostomy tube, or pancreatectomy.
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.