Advancing Science for Children with Epilepsy and Movement Disorders
In 2013 while Richard Neubig, professor and chair of MSU’s pharmacology and toxicology department, was conducting research on cardiovascular disease using mouse models with a Gnao1 protein mutation, one of the models died unexpectedly of a seizure, which begged the question of whether the mutation could be linked to a seizure disorder.
Further investigation indicated that this mouse model was prone to seizures and soon after, four children who had been diagnosed with Early Infantile Epileptic Encephalopathy (EIEE) were also found to have mutations in GNAO1, confirming that further study of mutations in the protein and its gene, Gnao1, was warranted.
As more children with unusual disorders had their genomes sequenced, movement disorders and accompanying developmental delays were added to the characteristics of those with the Gnao1 mutation. A newly defined neurological disorder, Neurodevelopmental Disorder with Involuntary Movements, is associated with mutations in Gnao1. Currently, approximately 100 children have been reported with 45 different mutations in Gnao1.
Two graduate students in Neubig’s lab, Huijie Feng, a doctoral student in the Department of Pharmacology and Toxicology, and Casandra Larrivee, a master’s student in the comparative medicine and integrative biology program, are studying mutations affecting the GαO protein and recently published some of their research findings in PLoS ONE. They have found different mutations within the gene correlating to different characteristics (phenotypes) of the movement disorders.
As patients are reported, Feng and Larrivee compile their genetic and clinical information. They then use specially designed mouse models to study the mutations and resulting phenotypes more fully.
“We wanted to develop a mouse model with a Gnao1 mutation to see if it replicated the clinical phenotype of the GNAO1-associated neurological disorders,” said Feng. “If so, it would be a valuable tool to understand the neural mechanisms underlying the complex phenotypic spectrum of patients with GNAO1 mutations.”
The mouse models are created at MSU’s Transgenic and Genome Editing Facility using CRISPR technology to modify the DNA sequences of embryonic cells to the target gene, so the genetic makeup of the mouse then matches the genetic mutation of a patient(s) with one of the specific disorders. The mouse colony is then expanded, so that Feng and Larrivee can test them. They currently have two mouse models, each matching one of the most prevalent Gnao1 mutations.
One of the mouse model’s phenotypes match the characteristics of children with a corresponding mutation in GNAO1, meaning that this model should be useful in mechanistic and preclinical studies of GNAO1-related movement disorders.
Feng and Larrivee’s current research involves compiling the various mutations and characterizing the associated phenotypes and underlying pathological mechanisms using different mouse models.
Feng and Larrivee test the mice developed for movement disorders using a battery of four behavioral tests to ensure that the model’s disorder characteristics correlate with that of the patients’. Each test unveils different aspects of how the mouse behaves under different conditions.
One tests how the mouse moves in a novel environment. A second tests coordination skills, specifically whether the mouse can maintain its balance on a rotating beam as it accelerates. A third tests forepaw strength and the rate of muscle fatigue, while the fourth, a modified mouse treadmill attached with a camera, examines gait, foot placement and multiple parameters associated with different movement disorders.
Mouse models with mutations that cause epilepsy in humans are tested for seizure susceptibility by using a drug to increase brain excitability to identify which group of mice develops seizures faster. These tests have established that the mouse model is positively linked to seizure disorders, confirming that this model can continue to be used for further study.
Feng and Larrivee will continue compiling and characterizing the mutations on Gnao1. Through greater understanding of the mutation’s various characteristics, they hope to eventually clarify the mechanisms of the neurological disorders associated with those mutations and ultimately develop therapeutic intervention for the disorders.
- Laura Probyn via MSU Today