GRIN families join together for neuroscience

Editor’s note: This post was a collaboration with MMG graduate student Megan Hockman.

They were brought together by their children’s epilepsies, and by rapid advances in genetic sequencing. Only a few years ago, these families would have been isolated, left to deal with their children’s seizures and neurological problems on their own. Now, they’ve organized themselves and are shaping the future of research.

Agonist binding domains of NMDA receptors, where several disease-causing mutations can be found. Adapted from Swanger et al, AJHG (2016).

In mid-September, parents of children affected by variations in GRIN genes gathered at Emory Conference Center to meet with scientists to discuss current research. GRIN disorders occur because of mutations in genes encoding NMDA receptors, which play key roles in memory, learning and neuronal development. NMDA receptors are a type of receptor for glutamate, the main excitatory neurotransmitter in the brain. The receptors themselves are encoded by multiple genes and assemble into tetramers. When their function is altered by mutations in one of these genes, symptoms appear in infancy or early childhood, usually including epilepsy and developmental delay.

The conference was the first time several patient advocacy groups oriented around GRIN-related disorders had met together, says Denise Rehner, president of the CureGRIN Foundation and mother of an affected child. For parents, this was an opportunity to connect with each other and advocacy groups, and to interact with scientists. For researchers, it was a chance to hear from those who are being impacted by their studies, and to discuss better ways to share data.

“We got a chance to explain to all the stakeholders – patient groups, foundations, companies – exactly what we do,” said Emory neuroscientist and conference organizer Stephen Traynelis, director of the Center for Functional Evaluation of Rare Variants. Traynelis and colleague Hongjie Yuan have been tracking the direct impacts of mutations on the function of the NMDA receptor. In doing so, they plan work with clinicians to compile registries, linking specific functional data to patient symptoms.

In addition to understanding underlying mechanisms and outcomes of GRIN disorders, researchers want to figure out how to treat affected children with existing drugs. Several options exist for targeting NMDA receptors, such as dextromethorphan (a cough suppressant) or memantine, approved for symptoms of Alzheimer’s. Traynelis and Yuan previously collaborated with the Undiagnosed Disease Program (now the Undiagnosed Disease Network) at the National Institutes of Health to investigate memantine as a treatment for a child with a GRIN2A mutation, showing that the drug could reduce seizure burden in one patient. Read more

Posted on September 30, 2019 by Quinn Eastman in Neuro Leave a comment

More on NMDA receptor variants + epilepsy/ID

NMDA receptors are complex electrochemical machines, important for signaling between brain cells. Rare mutations in the corresponding genes cause epilepsy and intellectual disability.

Pre-M1 helices in multi-subunit NMDA receptor. Adapted from Ogden et al PLOS Genetics (2017).

In Emory’s Department of Pharmacology, the Traynelis and Yuan labs have been harvesting the vast amounts of information now available from public genome databases, to better understand how changes in the NMDA receptor genes relate to function. (Take a “deeper dive” into their November 2016 publication on this topic here.)

Their recent paper in PLOS Genetics focuses on a particular region in the NMDA receptor, called the pre-M1 helix (see figure). It also includes experiments on whether drugs now used for Alzheimer’s disease, such as memantine, could be repurposed to have beneficial effects for patients with certain mutations. The in vitro data reported here could inform clinical use. Read more

Posted on January 31, 2017 by Quinn Eastman in Neuro Leave a comment

Deep dive into NMDA receptor variation

The study of human genetics has often focused on mutations that cause disease. When it comes to genetic variations in healthy people, scientists knew they were out there, but didn’t have a full picture of their extent. That is changing with the emergence of resources such as the Exome Aggregation Consortium or ExAC, which combines sequences for the protein-coding parts of the genome from more than 60,000 people into a database that continues to expand.

Rare mutations in the NMDA receptor genes cause epilepsy (GRIN2A) or intellectual disability (GRIN2B). Shown in blue are agonist binding domains of the receptors, where several disease-causing mutations can be found.

At Emory, the labs of Stephen Traynelis and Hongjie Yuan have published an analysis of ExAC data, focusing on the genes encoding two NMDA receptor subunits, GRIN2A and GRIN2B. These receptors are central to signaling between brain cells, and rare mutations in the corresponding genes cause epilepsy (GRIN2A) or intellectual disability (GRIN2B). GRIN2B mutations have also been linked with autism spectrum disorder.

Steve Traynelis and Hongjie Yuan

The new paper in the American Journal of Human Genetics makes a deep dive into ExAC data to explore the link between normal variation in the healthy population and regions of the proteins that harbor disease-causing mutations.

In addition, the paper provides a detailed look at how 25 mutations that were identified in individuals with neurologic disease actually affect the receptors. For some patients, this insight could potentially guide anticonvulsant treatment with a repurposed Alzheimer’s medication. Also included are three new mutations from patients identified by whole exome sequencing, one in GRIN2A and two in GRIN2B.

“This is one of the first analyses like this, where we’re mapping the spectrum of variation in a gene onto the structure of the corresponding protein,” says Traynelis, PhD, professor of pharmacology at Emory University School of Medicine. “We’re able to see that the disease mutations cluster where variation among the healthy population disappears.”

Heat map of agonist binding domain for GRIN2A. From Swanger et al AJHG (2016).

Postdoctoral fellow Sharon Swanger, PhD is first author of the paper, and Yuan, MD, PhD, assistant professor of pharmacology, is co-senior author.

It’s not always obvious, looking at the sequence of a given mutation, how it’s going to affect NMDA receptor function. Only introducing the altered gene into cells and studying protein function in the lab provides that information, Traynelis says.

NMDA receptors are complicated machines: mutations can affect how well they bind their ligands (glutamate and glycine), how they open and shut, or how they are processed onto the cell surface. On top of that complexity, mutations that make the receptors either stronger or weaker can both lead the brain into difficulty; within each gene, both types of mutation are associated with similar disorders. With some GRIN2A mutations, the functional changes identified in the lab were quite strong, but the effect on the brain was less dramatic (mild intellectual disability or speech disorder), suggesting that other genetic factors contribute to outcomes.

Clinical relevance

Traynelis and Yuan previously collaborated with the NIH’s Undiagnosed Disease Program to show that the Alzheimer’s medication memantine can be repurposed as an anticonvulsant, for a child with intractable epilepsy coming from a mutation in the GRIN2A gene. (Nature Communications, Annals of Clinical and Translational Neurology)

Memantine is an NMDA receptor antagonist, aimed at counteracting the overactivation of the receptor caused by the mutation. Memantine has also been used to treat children with epilepsy associated with mutations in the related GRIN2D gene. However, memantine doesn’t work on all activating mutations, and could have effects on the unmutated NMDA receptors in the brain as well. Traynelis reports that his clinical colleagues are developing guidelines for physicians on the use of memantine for children with GRIN gene mutations.

This study and related investigations were supported by funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (R01HD082373), the National Institute of Neurological Disorders and Stroke (R24NS092989), the Atlanta Clinical & Translational Science Institute (UL1TR000454), and CURE Epilepsy: Citizens United for Research in Epilepsy.

Posted on November 11, 2016 by Quinn Eastman in Neuro 2 Comments

Reviving drugs with anti-stroke potential, minus side effects

Neuroprotective drugs might seemÂ impractical or improbable right now, after twoÂ big clinical trials testing progesterone in traumatic brain injury didn’t work out. But oneÂ close observer of drug discovery isÂ predicting a “coming boom in brain medicines.” Maybe this research, which Emory scientists have been pursuing for a long time, will be part of it.

In the 1990s, neuroscientists identified a class of drugs that showed promise in the area of stroke. NMDA receptor antagonists could limit damage to the brain in animal models of stroke. But one problem complicated testing the drugs in a clinical setting: the side effects included disorientation and hallucinations.

Now researchers have found a potential path around this obstacle. The results were published in Neuron.

â€œWe have found neuroprotective compounds that can limit damage to the brain during ischemia associated with stroke and other brain injuries, but have minimal side effects,â€ says senior author Stephen Traynelis, PhD, professor of pharmacology at Emory University School of Medicine.

â€œThese compounds are most active when the pH is lowered by biochemical processes associated with injury of the surrounding tissue. This is a proof of concept study that shows this mechanism of action could potentially be exploited clinically in several conditions, such as stroke, traumatic brain injury and subarachnoid hemorrhage.â€ Read more

Posted on February 27, 2015 by Quinn Eastman in Neuro Leave a comment

Personalized molecular medicine part 3

This is a continuation of previous posts on individualized treatment for infantile-onset epilepsy, made possible by Emory scientists Stephen Traynelis and Hongjie Yuanâ€™s collaboration with the NIH Undiagnosed Diseases Program. A companion paper containing some clinical details was recently published in Annals of Clinical and Translational Neurology.

Memantine, which was found to be effective for this particular child, is normally used to treat symptoms of Alzheimerâ€™s disease. He has a mutation in a gene encoding a NMDA receptor, an important signaling molecule in the brain, which hyperactivates the receptor. Treatment with memantine reduced his seizure frequency from 11 per week to three per week, and eliminated one type of seizure, myoclonic jerks. It allowed doctors to taper off conventional anticonvulsant drugs, which were having little effect anyway. His cognitive ability has remained unchanged.

The team also discovered that the compound dextromethorphan, found in many over-the-counter cough medicines, was effective in the laboratory in counteracting the effects of a GRIN2A mutation found in another patient. However, these effects were mutually exclusive, because the molecular effects of the mutations are different; memantine helps L812M, while dextromethorphan helps N615K.

Yuan and Traynelis report they have an Fake Oakleys ongoing collaboration with UDP investigators to analyze the effects of mutations in NMDA receptor genes. That means more intriguing case reports are coming, they say.

Tyler Pierson, MD, PhD, lead author of the clinical paper who is now at Cedars-Sinai Medical Center in Los Angeles, and David Adams, MD, PhD, senior staff clinician at NIH, provided some additional information on the patient in the study, shown here in a Q + A format. Read more

Posted on March 4, 2014 by Quinn Eastman in Neuro 1 Comment

Personalized molecular medicine part 2

This is a continuation of the post from last week on the early-onset epilepsy patient, whom doctors were able to devise an individualized treatment for. The treatment was based on Emory research on the molecular effects of a mutation in the patientâ€™s GRIN2A gene, discovered through whole exome sequencing.*

For this patient, investigators were able to find the Ray Ban Baratas cause for a previously difficult to diagnose case, and then use a medication usually used for Alzheimerâ€™s disease (memantine) to reduce his seizure frequency.

Last week, I posed the question: how often do we move from a disease-causing mutation to tailored treatment? Read more

Posted on March 3, 2014 by Quinn Eastman in Cancer, Neuro Leave a comment

True personalized medicine: from mutation to treatment

Stephen Traynelis, PhD and Hongjie Yuan, MD, PhD

How often can doctors go from encountering a patient with a mysterious disease, to finding a mutation in a gene that causes that disease, to developing a treatment crafted for that mutation?

This is true personalized molecular medicine, but itâ€™s quite rare.

How rare this is, Iâ€™d like to explore more, but first I should explain the basics.

At Emory, Stephen Traynelis and Hongjie Yuan have been working with Tyler Pierson, David Adams, William Gahl, Cornelius Boerkoel and doctors at the National Institutes of Healthâ€™s Undiagnosed Diseases Program (UDP) to investigate the effects of mutations in the GRIN2A gene.

Their report on the molecular effects of one such mutation, which caused early-onset epilepsy and intractable seizures in a UDP patient, was recently published in Nature Communications.

With that information in hand, UDP investigators were able to repurpose an Alzheimerâ€™s medication as an anticonvulsant that was effective in reducing seizure frequency in that patient. [The details on that are still unpublished but coming soon.]

Posted on February 24, 2014 by Quinn Eastman in Neuro Leave a comment