See the paper by Matthew Judson in The Journal of Neuroscience.
Many individuals with Angelman syndrome (AS) have microcephaly—a smaller head and brain size—than typically developing individuals. This microcephaly is not present at birth, but becomes evident sometime during the first 18 months of life, indicating a problem with brain growth. During this early phase of development, the brain typically grows very quickly and must develop in a precise manner to support normal brain functions. In AS, the brain grows more slowly, and this correlates with developmental delay, impaired motor function, and EEG abnormalities. The ASF-funded research team, led by Ben Philpot, Ph.D., studied microcephaly in AS mice and sought to determine the cause of reduced brain size in the mice. The results were published in the August 2nd issue of The Journal of Neuroscience.
The team examined the brain growth of AS mice during early development and found that they develop microcephaly after birth. Although newborn AS mice have the same sized brains as their neuro-typical counterparts, the brains of AS mice grow more slowly, and are thus smaller than their neuro-typical littermates by the time they are juveniles. As with individuals with AS, this microcephaly persists into adulthood. Notably, Philpot’s group showed that changes in the amount of white matter accounted for most of the microcephaly in AS mice. White matter contains bundles of axons, which are the long, slender portions of neurons that transmit electrical signals to other neurons or muscles. Axons are coated with a substance called myelin, which acts to insulate the electrical activity of axons. Philpot and colleagues found that although the amount of myelin was normal in adult AS mice, the axons in AS mice were smaller in diameter than the mice without AS. These smaller axons correlated with deficits in nerve conduction in the AS mice. Future research will help determine exactly how the axon diameter deficit in AS mice arises during development, whether it might be related to delays in myelination, and how it could contribute to behavioral phenotypes.
White matter deficits have been previously reported in individuals with AS. The ASF recently funded a collaborative group including Drs. Ben Philpot, Mark Shen, Heather Hazlett, and Ron Thibert to study this process in children and young adults with AS. Preliminary data from this work was presented at the Angelman Syndrome Foundation’s 2017 Research Symposium. More work in this important area of brain research is needed to determine if the white matter deficits observed in individuals with AS are caused by changes in axon diameter, as predicted by Philpot’s recent findings in AS mice. Importantly, if the extent of white matter structural deficits proves to correlate with the severity of impairments in nerve conduction and motor skills performance in individuals with AS, then measurement of white matter may serve as a helpful biomarker to gauge responsiveness to a potential treatment.
ASF-funded research published in the Journal of Neurodevelopmental Disorders has identified that delta—a frequency of brain rhythms identifiable by EEG scans—can serve as a reliable biomarker for pre-clinical and clinical trials in Angelman syndrome. The research team, led by Dr. Mike Sidorov at the University of North Carolina-Chapel Hill, compared existing EEG data from the Angelman Syndrome Natural History Study to neuro-typical EEG data from Massachusetts General Hospital. The study showed that delta abnormalities can be seen across the brain of children with Angelman syndrome, and during both sleep and wake.
“We focused on delta because it is the most commonly reported abnormality in AS EEG scans,” said Sidorov. “In doing so, we consistently found that nearly every individual with AS has increased delta compared to neuro-typical individuals.” Most importantly, we found that delta abnormalities can be quantified, said Sidorov. “By reducing delta to a single number, we are able to track it reliably over time within individuals. We were thrilled with the result and believe delta has great potential for use as a biomarker and outcome measure in future clinical trials, as well as pre-clinical studies because we saw the same result in our mouse-model data.”
Few authentic biomarkers for Angelman syndrome have been found. Biomarkers must be objective, reliable, and repeatable in different settings in order to accurately determine whether a potential therapeutic is effective. This latest discovery checks all of those boxes. This ASF-funded published research takes a significant step forward in having viable tools to measure the success of pre-clinical and clinical drug trials.
Ovid Therapeutics, a privately held biopharmaceutical company based in New York City, announced that the U.S. Food and Drug Administration has granted orphan drug designation to OV101 for the treatment of patients with Angelman syndrome.
See the press release.
ASF-funded research conducted at Dr. Ben Philpot’s lab at the University of North Carolina-Chapel Hill has answered some questions about UBE3A’s role in seizures in individuals with Angelman syndrome, and also illustrated additional work that needs to be done.
Published in the prestigious research journal, Neuron, the research sought to answer the question: how are seizures affected by where—not just when—UBE3A is expressed in the brain?
The research team, led by Matt Judson, PhD in Philpot’s lab, found that UBE3A loss specifically from GABAergic neurons can cause seizures in an Angelman syndrome mouse model. It was previously unclear which cell classes were relevant, and there were reasons to believe that UBE3A loss in both excitatory and inhibitory neurons was important. The research showed that loss of UBE3A from inhibitory neurons, but not excitatory neurons, is enough to cause seizures. This illustrates that both timing AND location of UBE3A restoration are important in reducing seizures in AS. This is relevant to gene therapy and other treatment approaches. More work needs to be done to determine different cell types and pathways to further understand the link between UBE3A and seizures in Angelman syndrome.
See an article about the research in Spectrum.
Access the full issue (requires paid subscription).