Society for Neuroscience
New Clues to Autism
Speakers: Daniel H. Geschwind, MD, PhD, University of California, Los Angeles; Eric Peterson, PhD, University of Colorado; Brendon Nacewicz, University of Wisconsin, Madison; Aysenil Belger, PhD, University of North Carolina-Chapel Hill, and James S. Sutcliffe, PhD, Vanderbilt University, Nashville, Tennessee
New research has found that some of the brain abnormalities and behaviors associated with autism also are present in the parents and siblings of individuals with the disorder. Rare mutations on a specific gene appear to be risk factors for autism. Scientists have also discovered that avoidance of eye contact with other people is not, as previously believed, a primary cause of the social impairments observed in autism.
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All of these studies promise to shed light on more effective methods of diagnosis and treatment. Autism affects as many as 24,000 children born in the U.S. each year. It is a brain disorder that impairs a person’s ability to think, feel, communicate, and relate appropriately to the outside world. These behaviors can range from mild to severely disabling, but their impact on the lives of individuals with the disorder and on their families is almost always devastating. People with autism often have other debilitating brain disorders, including attention-deficit/hyperactivity disorder, obsessive-compulsive disorder (OCD), epilepsy, and depression.
Although the exact cause of autism is unknown, experts believe that it is associated with abnormal brain developments that emerge in part as a result of genetic factors. A better understanding of what exactly goes wrong in the developing brains of autistic children might be able to help scientists identify the genes involved with autism and thus to generate better methods of diagnosing and treating the disorder.
Many areas of the brain have been implicated as an etiologic factor, but pinpointing specific brain structures has proved challenging. Brain development and cognitive maturation are difficult to control in clinical studies of autistic children.
Researchers at the University of Colorado, Colorado State University, and the University of Denver decided to study the brains of parents of autistic children to see whether they also had abnormalities associated with the disorder. If they did, those abnormalities might be the heritable ones involved in the emergence of autism.
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For the study, 40 parents of autistic children and 40 age-matched and sex-matched controls received magnetic resonance imaging (MRI) brain scans. Scientists identified many brain regions in which “the autism parent group was either smaller or larger than in the brains of the adults with a negative family history,” reports Eric Peterson, PhD. These areas include the cerebellum, which plays a role in cognitive thinking (speech, learning, emotions, and attention) and in motor function, and the basal ganglia, a brain region associated with compulsive and ritualistic behavior. People with autism often have difficulty with changes in their routines and can develop patterns of repetitive behaviors.
These findings offer hints as to which brain abnormalities might be heritable with autism. One of the next steps, says Dr. Peterson, is to confirm the findings in studies on pairs of twins when only one twin has autism and to use functional brain imaging for family members to see whether the malfunctioning of those same brain regions is also heritable.
At the University of Wisconsin-Madison (UW), researchers found that the non-autistic brothers of people with autism show the same avoidance of eye contact as their autistic siblings when they viewed images of strangers and family members. Abnormal eye contact is common in people with autism, and it is often one of the behaviors first noticed in children with the disorder. The non-autistic brothers, like their autistic siblings, had smaller-than-normal amygdalas, an area of the brain involved in understanding emotional facial expressions and in feeling fear in social situations. Apcalis Oral Jelly
Using computerized technology, the UW researchers measured the amount of time that three groups of participants, 6 to 18 years of age, spent looking at the eyes of people in pictures. The groups included nine boys with autism, nine non-autistic brothers of individuals with autism, and nine boys with typical development. Intelligence quotient (IQ) scores were similar for the non-autistic brothers (average, 120) and the control group (average, 119) but were lower for the autistic group (95). Nevertheless, the autistic subjects and the non-autistic brothers were most similar when it came to eye contact: both groups showed decreased eye contact in relation to the control group. The low incidence of eye contact occurred even when the boys were shown pictures of family and friends. Thus, the behavior did not reflect inherited shyness.
The researchers also examined brain structures in all three groups. The brothers of individuals with autism had smaller amygdalas than the control group. In fact, amygdala volumes were similar to those of their autistic siblings.
“This suggests that other brain systems must be able to compensate for this abnormality in the non-autistic brothers,” says Brendon Nacewicz, one of the study’s authors. “Multiple brain systems must therefore be affected to develop the full syndrome of autism.”
At the University of North Carolina-Chapel Hill (UNC), researchers made the striking discovery that although people with autism tend to avoid looking directly at faces, when they do focus on faces, their brains respond in ways similar to those of people who do not have autism. This finding suggests that behavioral interventions may help these people improve their ability to interact socially.
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Using functional magnetic resonance imaging (fMRI), a noninvasive technique, Gabriel Dichter, PhD, and Aysenil Belger, PhD, asked subjects to perform a task that required them to attend to certain items in the environment while disregarding other items. The participants were shown pictures of arrows (non-social items) and faces (social items). They were then asked to report the direction (left or right) in which the arrows pointed.
With both social and non-social items, the autistic participants showed markedly less activity than the controls in the “executive” regions of the brain (including portions of the frontal lobes), where specialized tasks (e.g., sifting through complex information, selecting task-appropriate responses or inhibiting task-inappropriate ones) take place.
With the social items, however, the results were surprising. Responses in the executive areas differed in the two groups, but responses in the areas of the brain that process faces— including the fusiform gyrus—were remarkably similar.
This new research, conducted with support from the National Institute of Mental Health (NIMH) Studies to Advance Autism Research and Treatment (STAART) Network and the UNC Neurodevelopmental Disorders Research Center, has exciting implications.
“Since the brain seems capable of responding to faces when attention is directed toward faces, purely behavioral interventions that instruct individuals with autism to look at faces may help both to increase the brain’s responsiveness to social cues and to improve the quality of social interactions,” Dr. Dichter says.
Researchers at Vanderbilt University report that several rare mutations within a specific gene (the serotonin transporter, or SERT) are risk factors for autism. These findings may eventually make it possible to test autistic children for these gene variants, just as children can be tested for cystic fibrosis, a disease that is linked to a single gene but is triggered by many different mutations. Evidence suggests that early diagnosis and intervention (before age 3) results in better outcomes for autistic children. generic cialis 20mg
The SERT gene regulates serotonin levels in the brain. About 25% of people with autism have elevated levels of serotonin, and selective serotonin reuptake inhibitors (SSRIs) have helped to ease the symptoms of autism in some patients.
Previous research attempting to link the SERT gene to autism had been promising but inconclusive.
“Either this was not the gene, or there had to be different genetic variants that were acting differently in different people,” says James Sutcliffe, PhD.
Hoping to find rare mutations involved in a person’s risk of developing autism, Dr. Sutcliffe and his colleagues took DNA samples from 120 families likely to possess a genetic risk factor on chromosome 17 (where the SERT gene resides). They found 19 different SERT mutations (or variants) in families with more than one male with autism. (The finding that families with multiple males with autism had these variants is consistent with the higher prevalence of autism among males; four times as many males as females are affected by the disorder.)
Four of the 19 SERT mutations were in “coding” regions, or areas of the gene that are translated into protein.
“These variants were significantly associated with increased rigid-compulsive behaviors,” notes Dr. Sutcliffe.
Such behaviors are common in autism and of related disorders, such as OCD.
These investigators also discovered that two intracellular signaling pathways in the brain—p38MAPK and PKG—”go haywire” in the presence of mutated SERT genes. This might explain how SERT mutations disrupt serotonin signaling in autism. Drugs that target these pathways are being investigated for the treatment of inflammation, cancer, and other disorders unrelated to autism. buy cialis soft tabs
However, it is still unclear which aspects of the autism syndrome or phenotype are related to a particular genetic risk factor and whether these risk factors are specific for autism or cause more general brain dysfunction.
