KATP Defect With Diffuse Congenital Hyperinsulinism
What is KATP defect with diffuse congenital hyperinsulinism?
Congenital hyperinsulinism (HI) is a genetic disorder in which the insulin cells of the pancreas secrete too much insulin. Excess insulin causes low blood sugar (hypoglycemia). In children with HI, the secretion of insulin is not properly regulated, causing excess insulin secretion and low blood sugar.
In children with KATP defect with diffuse congenital hyperinsulinism, all the beta cells in the pancreas are affected. Potassium channels in the beta cells (named KATP channels), which regulate insulin secretion, do not work properly.
KATP defect with diffuse HI is caused by a defect in the SUR1 component of the KATP channel (SUR1= Sulfonylurea receptor; also known by its gene name, ABCC8).
The same type of disease can be caused by a defect in the other component of the potassium channel, Kir6.2 (Kir6.2= Potassium ion channel; also known by its gene name, KCNJ11)
In most cases, inheritance of the genetic defect is recessive, meaning the gene of the mother and father must be defective to cause the disease.
KATP defect with diffuse congenital hyperinsulinism often causes extremely high birth weight and severe low blood glucoses in the first days of life.
This disease also cause 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.
Some forms of congenital hyperinsulinism can be medically managed and some require surgery. Children with KATP defect with diffuse congenital hyperinsulinism usually require surgery to remove 95-98% of the pancreas, which is called a pancreatectomy. This form of HI usually cannot be controlled with diazoxide (Proglycem) medication.
About 50% of children who have had a 95-98% subtotal pancreatectomy may continue to require treatment for hypoglycemia, including gastrostomy tube feedings (for which a gastrostomy tube is placed at the time of surgery) and octreotide injections.
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.