Group items tagged

When the production of neuroligin-3 in the mice was reactivated, the nerve cells reduced the production of the glutamate receptors to a normal level and the structural defects in the brain typical for autism were gone. Consequently, these glutamate receptors could be targeted in the development of drugs that could stop autism from developing or even reverse it.

Developmental abnormalities in the mirror neuron system may contribute to social deficits in autism.

Now, a new study published in Biological Psychiatry reports that the mirror system in individuals with autism is not actually broken, but simply delayed.

While most of us have their strongest mirror activity while they are young, autistic individuals seem to have a weak mirror system in their youth, but their mirror activity increases with age, is normal by about age 30 and unusually high thereafter.

“Having at our fingertips detailed information about when and where specific gene products are expressed in the brain brings new hope for understanding how this process can go awry in schizophrenia, autism and other brain disorders,” said NIMH Director Thomas R. Insel, M.D.

Among key findings in the prefrontal cortex:Individual genetic variations are profoundly linked to expression patterns. The most similarity across individuals is detected early in development and again as we approach the end of life.Different types of related genes are expressed during prenatal development, infancy, and childhood, so that each of these stages shows a relatively distinct transcriptional identity. Three-fourths of genes reverse their direction of expression after birth, with most switching from on to off.Expression of genes involved in cell division declines prenatally and in infancy, while expression of genes important for making synapses, or connections between brain cells, increases. In contrast, genes required for neuronal projections decline after birth – likely as unused connections are pruned.By the time we reach our 50s, overall gene expression begins to increase, mirroring the sharp reversal of fetal expression changes that occur in infancy.Genetic variation in the genome as a whole showed no effect on variation in the transcriptome as a whole, despite how genetically distant individuals might be. Hence, human cortexes have a consistent molecular architecture, despite our diversity.

Among key findings:Over 90 percent of the genes expressed in the brain are differentially regulated across brain regions and/or over developmental time periods. There are also widespread differences across region and time periods in the combination of a gene’s exons that are expressed.Timing and location are far more influential in regulating gene expression than gender, ethnicity or individual variation.Among 29 modules of co-expressed genes identified, each had distinct expression patterns and represented different biological processes. Genetic variation in some of the most well-connected genes in these modules, called hub genes, has previously been linked to mental disorders, including schizophrenia and depression.Telltale similarities in expression profiles with genes previously implicated in schizophrenia and autism are providing leads to discovery of other genes potentially involved in those disorders.Sex differences in the risk for certain mental disorders may be traceable to transcriptional mechanisms. More than three-fourths of 159 genes expressed differentially between the sexes were male-biased, most prenatally. Some genes found to have such sex-biased expression had previously been associated with disorders that affect males more than females, such as schizophrenia, Williams syndrome, and autism.

It turns out that in all three of the primary cortices -- visual, auditory and somatosensory -- we did not see the typical response trial after trial in the individuals with autism. Instead, we saw considerable variability -- sometimes a strong response, sometimes a weak response. The fact that we did not see precise responses in autism was a really important result. It suggests that there is something fundamental that is altered in the cortical responses in autism. This variability in the brain response might also possibly explain why individuals with autism find visual stimulation, touch and sound to be so strong and overwhelming.

We know from genetic research that many of the neurobiological changes that occur in autism have to do with changes at the level of the synapse, the way that information is transmitted from one neuron to another.

Now, researchers led by Mustafa Sahin, MD, PhD, of Children's Department of Neurology, provide evidence that mutations in one of the TSC's causative genes, known as TSC2, prevent growing nerve fibers (axons) from finding their proper destinations in the developing brain.

Sahin and colleagues showed that when mouse neurons were deficient in TSC2, their axons failed to land in the right places.

Further investigation showed that the axons' tips, known as "growth cones," did not respond to navigation cues from a group of molecules called ephrins.

The Howard Hughes Medical Institute describes how researchers using "high-throughput gene sequencing technology" were able to identify several de novo or spontaneous gene mutations in 20 children with sporadic autism spectrum disorders -- that is, their family members showed no other sign of autism.

The team identified 21 spontaneous mutations -- meaning they weren't inherited from either parent -- in the children's DNA. Eleven of these were mutations that would alter the protein encoded by the affected gene. In four of the 20 children, the researchers found mutations that were severe, some of which have been previously linked to autism, intellectual disability, and epilepsy.

one child had a mutation in the GRIN2B gene, which is crucial for neuronal signaling.

The results show for the first time the role of the SYN1 gene in autism, in addition to epilepsy, and strengthen the hypothesis that a deregulation of the function of synapse because of this mutation is the cause of both diseases

until now, no other genetic study of humans has made this demonstration.

The different forms of autism are often genetic in origin and nearly a third of people with autism also suffer from epilepsy.