How a single gene causes severe mental retardationMay 11th, 2009 - 11:59 am ICT by ANI
London, May 11 (ANI): Experiments on mice conducted by scientists at Duke University Medical Center and the University of North Carolina have significant insights into how a single disrupted gene can cause a form of severe mental retardation, Angelman syndrome.
The researchers have found that the UBE3A gene is key to the formation of neurons in the brain, and the adjustment of their connections to other neurons for storing sensory information.
The researchers also observed that when the mice were deprived of sensory stimulation, the brain connections could be recovered.
They said that that finding indicated a pharmaceutical or behavioural treatment might be possible in future.
“We wanted to look at an animal model to learn if this experience-dependent reorganization of the cortex was abnormal in animals that were missing the gene,” Nature magazine quoted Dr. Michael Ehlers, a Duke professor of neurobiology and co-senior author of the study, as saying.
“We looked at the visual cortex, because in this well-studied model, we could precisely control the sensory stimulus and study the mice in the light or the dark. We speculated that similar deficits may be happening in areas of the cortex that are important for language, cognition and emotion, all of which are quite abnormal in Angelman syndrome patients,” he added.
The study showed that brains cells in Angelman syndrome mice lacked the ability to appropriately strengthen or weaken in the cortex, an area of the brain important for cognitive abilities.
“Instead of studying a complex learning model, we studied how connections between brain cells change in visual areas of mice exposed to light or kept in darkness. This approach revealed that brain cells in normal mice can modify their connections in response to changes in visual experiences, while the brain cells in Angelman syndrome mice could not,” said Dr. Koji Yashiro, a former University of North Carolina graduate student and lead author of the study.
According to the researchers, the inability of brain cells to encode information from experiences in the Angelman syndrome model suggested that it was the basis for the profound learning difficulties in these patients.
They were surprised to see that the plasticity of the cellular connections could be restored in visual areas of the brain after brief periods of visual deprivation.
“By showing that brain plasticity can be restored in Angelman syndrome model mice, our findings suggest that brain cells in Angelman syndrome patients maintain a latent ability to express plasticity. We are now collaborating to find a way to tap into this latent plasticity, as this could offer a treatment, or even a cure, for Angelman syndrome,” said Dr. Ben Philpot, a University of North Carolina professor in Cell and Molecular Physiology and co-senior author of the study.
Ehlers believes that perhaps some of these developmental brain disorders are a form of social and cognitive blindness. In a condition known as amblyopia, or cortical blindness, the eye can function normally, but past a critical period, the brain cannot process the sensory input correctly.
“We think that children with Angelman syndrome may have a condition in which sensory experience dampens down plasticity and affects learning. One important aspect of our findings is that sensory manipulations recovered plasticity, suggesting that the underlying substrates for plasticity are intact in mice. If the same thing holds true for the human disease, there may be a chance to improve brain function,” Ehlers said.
A research article on the study has been published in the journal Nature Neuroscience. (ANI)
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