New test detects parent-of-origin in hereditary eye cancer

This article is published in the UW Medicine newsroom here.

UW ophthalmologists who care for children with retinoblastoma, a rare, hereditary eye cancer, have developed a novel blood test that can tell which parent’s DNA carried the disease-causing RB1 gene mutation.  

That distinction is meaningful because male and female copies of the mutation are associated with different disease trajectories, the researchers found, and likely would influence doctors’ treatment recommendations.  

“Depending on which copy you have, that could reflect the cancer’s severity and its likely response to chemotherapy,” said Dr. Debarshi Mustafi, an assistant professor of ophthalmology at the University of Washington School of Medicine. 

Drs. Debarshi Mustafi and Andrew Stacey of UW Medicine and Seattle Children's were the study's co-lead authors.

The new gene-sequencing technique that powers the blood test can also detect parent-of-origin even when the child carries a de novo variant, one that arises spontaneously and is not present in either parent. These de novo cases are the predominant cause of all cancers and account for 90% of all inherited cases of retinoblastoma. 

The findings were published Dec. 26 in the journal JCI Insight. The co-lead authors were Mustafi and Dr. Andrew Stacey, an associate professor of ophthalmology at the UW School of Medicine. Both are surgeons at Seattle Children's Hospital, where they treat pediatric patients with retinal diseases. 

Retinoblastoma is rare, affecting about 200 to 300 children a year in the United States. The condition disrupts the normal development of the retina, the light-sensitive tissue in the back of the eye. Starting during fetal development, these cancerous cells proliferate out of control and form tumors.  

Children in developed countries are diagnosed by age 2, on average, Mustafi said. Often an early hint of the disease is an eye discoloration seen in a photo of the child, or an eye that has trouble tracking.  

Without treatment, retinoblastoma can spread through the optic nerve into the brain. Even when tumors are ablated with radiation or treated with chemotherapy, related metastases can emerge years later in distant organs.  

“If we can catch the tumor early, we can save the eye — and what we found in this study is that your parent-of-origin makes a difference here: When mutations came from the maternal copy, patients’ eyes were saved more often,” Mustafi said. “If they got it from the paternal DNA, we are less likely able to save the eye. Our preliminary data also shows that a secondary cancer such as sarcoma is more likely with the paternal mutation.” 

 

In a patient whose retinoblastoma stems from maternal inheritance, left, there is only a small tumor in the eye (denoted by white arrow) that responded well to treatment. Comparatively, in a patient with paternal inheritance, an extensive tumor burden affects underlying retinal structures.  (Courtesy of Dr. Debarshi Mustafi)

Awareness of parental disease origin, he added, could influence doctors to recommend aggressive therapies earlier in a child’s course of care, or to take more, or fewer, steps to save an affected eye.  

“We could counsel a family that, instead of going for these heroic measures, they may be better off taking the eye out and preventing the spread,” Mustafi said. “Our finding will not only inform how we treat a child in the beginning, but how we screen them for their entire life. We think this will have a huge impact on surveillance of cancer patients.” 

Creating the novel genetic test 

The researchers didn’t set out to create a novel genetic test for retinoblastoma. Mustafi described a 2023 conversation in which Stacey expressed frustration with the wait — typically one to six months — to get a commercial lab’s confirmation of whether a child has the RB1 mutation.  

“Our initial goal was to see if we could confirm the diagnosis faster. I told him that my lab was working on a method that could get him an answer in a day or two,” Mustafi said.  

A white reflection seen in the pupil (visible in the child's right eye), also known as leukocoria or cat's eye reflex, is a common symptom of retinoblastoma. 

His lab scientists ended up devising a gene-sequencing technique that simultaneously identifies not only the RB1 mutation, but also other DNA-based modifications.  

“Two things happen with DNA: One is a mutation, in which some of your normal genetic code is switched out for other code. Your DNA is changed. But another thing that happens, called methylation, is a kind of modification signal that is switched on or off,” Mustafi said.  

“With RB1, we saw that Dad’s copy of the modification signal is distinct from Mom’s” he added. “So, when we put the mutation together with the modification signal, we were able to tell from the child’s blood whether they got the mother’s or the father’s chromosomal copy — and without having to test either parent.” 

They also met their goal of a 24-hour turnaround for diagnostic results. 

The experimental gene-sequencing technique’s accuracy was validated with blood samples from 16 pediatric patients at Seattle Children’s. Seven had familial-origin cases and nine had de novo disease.  

“The ability to assign parent-of-origin in all cases of retinoblastoma showed that harboring disease-causing variants on the paternally inherited allele, whether arising familial or de novo, is associated with more advanced cancer staging at presentation and significantly greater risk of chemotherapy failure,” the study authors wrote. 

[Editor’s note: The published paper details the genetic test’s methodology, instrumentation and development.] 

The new test likely will have applications for other genetic diseases in which parent-of-origin influences patients’ risk, Mustafi suggested. First, though, the researchers will measure its predictive accuracy in a larger group of patients.   

“We are partnering on a clinical trial with other large institutions that see a lot of retinoblastoma, like St. Jude's Research Hospital (Memphis), MD Anderson (Houston) and Children's Hospital (Los Angeles),” he said. 

The study received funding (K08EY033789) from the National Eye Institute, part of the National Institutes of Health, and from the Gerber Foundation.