Scientists develop model to understand rare brain disease found in 40 kids worldwide

Though he can’t walk, talk or eat by himself, Adam Banet, 9, has a big smile.

When he was three months old, his parents, Eden and Gilad Banet, took their firstborn son for a regular check-up and were told he had developmental delays. When he was eight months old, they discovered through genetic testing that Adam has a rare genetic disorder caused by a mutation in the GRIN2D gene, a protein crucial for brain function.

There are only 40 children around the world who have been identified with this non-hereditary mutation, which causes developmental epilepsy, significant motor and cognitive delays, and in some cases, premature death.

In a race to help Adam, the family turned to Tel Aviv University scientists, who now say that after six years of research, they have developed a mouse model that mimics the disease’s characteristics, enabling them to test a variety of drugs and genetic therapies, and offering hope to the affected children and their families.

“This mutation is rare, but it’s in a protein that’s very important for brain function,” lead researcher Prof. Moran Rubinstein of the Sagol School of Neuroscience told The Times of Israel in a recent phone interview. “Our research is a gateway to understanding how this protein works in normal brain function and what happens when it malfunctions.”

The study, co-led by Prof. Karen Avraham, dean of the university’s Gray Faculty of Medical and Health Sciences, students, and researchers from Columbia University, was recently published in the peer-reviewed journal Brain.

Eden Banet told The Times of Israel that when she and her husband first learned of Adam’s disorder, it was a few months after the publication of the “first and only study about GRIN2D gene mutation.”

“We’re engineers, not scientists, and if the study had been published any later, we wouldn’t have known what to do,” she said.

The couple approached Avraham, a geneticist, who agreed to form a research group that the Banets financed with help from family, friends, and a crowdfunding campaign.

Developing mouse models with the same mutation

To understand how the disorder works, Rubinstein said the team had to build a mouse model with the GRIN2D mutation.

However, the mice were so severely affected by the disorder that they died within their first weeks of life, before any experiments could be conducted.

Rubinstein said this showed that the mouse model accurately replicated aspects of the human disease. But it also posed a major challenge because it was impossible to produce enough mice for research.

To overcome this, the researchers used genetic engineering tools to create a strain of mice that carried the mutation without developing symptoms, allowing them to breed offspring in which half were healthy and half were affected.

The affected offspring displayed symptoms similar to those of human patients; most survived only a few weeks, with only a few living up to three months. The researchers examined their behavior and development at four stages: two weeks old (infancy), three weeks old (when mice transition to solid food, roughly equivalent to one-year-old children), four weeks old (roughly equivalent to six-year-old children), and five weeks old (early sexual maturity).

Neurological symptoms such as epilepsy, hyperactivity, and severe motor impairments were evident in the mice from infancy, she said. In contrast,  cognitive impairment appeared later and gradually worsened. Additionally, the affected mice had a short lifespan.

“Most did not survive to sexual maturity, dying from severe seizures,” Rubinstein said.

“Because the disease is so rare, its progression over time is not well understood,” she explained. “The mouse model helped us characterize its symptoms at different ages, and the tests we performed revealed interesting findings.”

She said the research reveals some of the mechanisms that are found both in neuro-developmental disorders early in life and neurodegenerative disorders late in life.

In another experiment, the researchers examined communication between neurons in the mice’s brains, particularly in the cerebellum, which controls motor function.

‘We are on the right track’

The analysis showed that by the age of two weeks, there was a decrease in the mice’s neuronal activity, bringing on pathological changes. Later, as the mice matured, activity levels returned to normal, but defective communication between neurons developed. Finally, the researchers found structural changes in the neurons themselves. These findings help elucidate the disease’s underlying mechanisms.

EEG tests conducted on the affected mice revealed a unique pattern that also characterizes the disease in humans.

“In most forms of epilepsy, seizures result from disrupted brain activity, but between seizures, brain activity is relatively normal,” Rubinstein said. “But in this disease, both in children and in the mice, brain activity is continuously disrupted. Moreover, using specific metrics we developed, we identified the same abnormalities in both mice and humans, an especially strong indication of the model’s validity.”

The researchers have also tested the effects of various drugs on the mice. Rubinstein said that some of the experimental drugs they are testing give “Adam’s parents hope that we are on the right track.”

“There’s usually a gap between researchers in the lab and patients, but the researchers all know us and Adam,” said Gilad. “We work closely together.”

“We can’t say that Adam suffers because he can’t tell us,” Eden said. “We want to heal him and the other kids with this mutation as soon as possible.”