Published onHI Hope
Much progress has been made over the last 25 years when it comes to identifying the genetic mutation that is causing a child’s congenital hyperinsulinism (HI).
As genetic testing has become more sophisticated and faster, about 22 genes have been implicated as leading to HI, when syndromic forms such a Beckwith-Wiedemann syndrome, Kabuki syndrome and Sotos syndrome are included. Many of those discoveries have been made right here in the Congenital Hyperinsulinism Center at Children’s Hospital of Philadelphia (CHOP).
Even with these advances, for about half of all patients with HI, genetic testing comes back as negative, meaning no known gene mutation was found. Specifically, in children who do not respond to the front-line medication diazoxide and require surgery to control their HI, about 10% do not have a known genetic mutation — even when tissue from the pancreas itself is tested. For children who are diazoxide-responsive and therefore can medically manage their HI, 50% have negative genetics.
No pancreatectomy, no pancreatic tissue to test
Our research team, led by Diva De León-Crutchlow, MD, MSCE, Director of the CHOP HI Center and Chief of the Division of Endocrinology and Diabetes, has recently published a paper demonstrating the presence of mutations in known HI genes in the pancreas of children who required pancreatectomy for diazoxide-unresponsive HI but whose genetic testing from peripheral blood was negative.
“It is possible that some patients who are medically managed also have a known genetic mutation that is only present in cells in their pancreas,” says HI researcher Kara Boodhansingh, BS, “but because they didn’t have a pancreatectomy, we don’t have pancreatic tissue to test.”
When a child has HI that requires ongoing treatment, parents appreciate knowing the genetics, when it is available. It gives them clues as to how their child’s disease may act in the future, since some types become easier to manage as the child grows, goes through puberty and moves into adulthood. Known genetics also help families with decisions on having another child and, in the future, will help the patient with their own family planning.
Recognizing the importance of this information, the HI Center’s research arm is actively searching for ways to give families the answers they seek.
Circulating cell-free DNA
One path of research focuses on teasing answers from circulating cell-free DNA. This research seeks to build on the knowledge that in some cases — for example, pregnant women and cancer patients — degraded DNA is released, or shed, from cells into the blood stream. A pregnant woman has circulating cell-free DNA shed from the fetus in her blood; a cancer patient may have circulating cell-free DNA shed by their tumor in their blood.
The HI lab is studying blood samples taken from medically managed, negative genetics patients to see if there is circulating cell-free DNA shed from the pancreas that might yield a mutation in one of the known HI genes.
“This research is still in the early stages, but hopefully will give us a way to uncover a known mutation in nonsurgical patients,” Boodhansingh says.
Whole exome and genome sequencing
A second area of research takes advantage of the advances in overall genetic testing.
Whole exome sequencing covers 20,300 genes; whole genome sequencing includes 30,000-plus genes and also is able to find changes in the noncoding sections of DNA within genes, called introns.
Ongoing research at CHOP studies samples from families that have at least two members with HI and negative genetics. It could be two siblings or a parent and a child. A nonaffected family member’s sample is also included.
“It’s a small pool,” Boodhansingh says, “about seven or eight families, but using families is important because it helps the focus our attention a little bit more on variants that show up in both family members.”
Results so far have revealed changes in a noncoding intronic region of genes that have not been previously implicated in HI. Genes are composed of exons and introns. Proteins are made from the exonic regions of the gene, while the introns are spliced out. Most mutations that occur in HI genes occur in exonic gene regions, thereby disrupting the protein sequence and altering its function. However, noncoding mutations in introns may have implications for genetic expression.
“We’re not yet sure if these changes cause HI,” Boodhansingh says, “so that’s what we’re working on. Once you find a variant, then you need to do more studies to understand how it might cause HI.”
While we recognize waiting for the discovery of additional genetic mutation can be frustrating, be assured that the HI Center is working toward finding answers for all children with negative genetics.