An analysis of autism research covering genetics, brain imaging, and cognition led by Laurent Mottron of the University of Montreal has overhauled our understanding of why autism potentially occurs, develops and results in a diversity of symptoms.
The team of senior academics involved in the project calls it the “Trigger-Threshold-Target” model. Brain plasticity refers to the brain’s ability to respond and remodel itself, and this model is based on the idea that autism is a genetically induced plastic reaction.
A new study provides the most definitive characterization of the autism-like intellectual disability disorder Christianson syndrome and provides the first diagnostic criteria to help doctors and families identify and understand the condition. Initial evidence suggests CS could affect tens of thousands of boys worldwide.
Because the severe autism-like condition Christianson syndrome was first reported only in 1999 and some symptoms take more than a decade to appear, families and doctors urgently need fundamental information about it. A new study that doubles the number of cases now documented in the scientific literature provides the most definitive characterization of CS to date. The authors of the study propose the first diagnostic criteria for the condition.
“We’re hoping that clinicians will use these criteria and that there will be more awareness among clinicians and the community about Christianson syndrome,” said Dr. Eric Morrow, assistant professor of biology and psychiatry and human behavior at Brown University and senior author of the study in press in Annals of Neurology. “We’re also hoping this study will impart an opportunity for families to predict what to expect for their child and what’s a part of the syndrome.”
There are new clues about malfunctions in brain cells that contribute to intellectual disability and possibly other developmental brain disorders.
Mutations in a gene called oligophrenin-1 (OPHN1) – located on the X chromosome – have previously been linked to X-linked intellectual disability (also known as X-linked mental retardation), a condition that affects boys disproportionately and could account for as much as one-fifth of all intellectual disability among males.
Several different mutations in the OPHN1 gene have been identified to date, all of which perturb nerve cells’ manufacture of OPHN1 protein. Previously, Van Aelst and colleagues demonstrated that OPHN1 has a vital role in synaptic plasticity, the process through which adjacent nerve cells adjust the strength of their connections. Cells in the brain are constantly adjusting connection strength as they respond to streams of stimuli.
The new discovery shows how OPHN1 is involved in the trafficking of AMPARs, an essential feature of plasticity in neurons. Neurons move receptors away from synapses into their interior and then back to the surface of synapses to control connection strength. At the synaptic surface, receptors provide an opportunity for the docking of neurotransmitters, in this case glutamate molecules. After a cell has fired, surface receptors are typically brought back into the interior, where they are recycled for future use.
Scientists from the Florida campus of The Scripps Research Institute (TSRI) have shed light on how a specific kind of genetic mutation can cause damage during early brain development that results in lifelong learning and behavioral disabilities.
In humans, mutations in Syngap1 are known to cause devastating forms of intellectual disability and epilepsy.
In the study, Rumbaugh and his colleagues used a mouse model to show that mutations in Syngap1 damage the development of a kind of neuron known as glutamatergic neurons in the young forebrain, leading to intellectual disability. Higher cognitive processes, such as language, reasoning and memory arise in children as the forebrain develops.
Repairing damaging Syngap1 mutations in these specific neurons during development prevented cognitive abnormalities, while repairing the gene in other kinds of neurons and in other locations had no effect.