Posts tagged ASD

(Source: msutoday.msu.edu)

Findings in bacteria, yeast, mice show how flawed transport gene contributes to the condition

Researchers say it’s clear that some cases of autism are hereditary, but have struggled to draw direct links between the condition and particular genes. Now a team at the Johns Hopkins University School of Medicine, Tel Aviv University and Technion-Israel Institute of Technology has devised a process for connecting a suspect gene to its function in autism.

In a report in the Sept. 25 issue of Nature Communications, the scientists say mutations in one such autism-linked gene, dubbed NHE9, which is involved in transporting substances in and out of structures within the cell, causes communication problems among brain cells that likely contribute to autism.

“Autism is considered one of the most inheritable neurological disorders, but it is also the most complex,” says Rajini Rao, Ph.D., a professor of physiology in the Institute for Basic Biomedical Sciences at the Johns Hopkins University School of Medicine. “There are hundreds of candidate genes to sort through, and a single genetic variant may have different effects even within the same family. This makes it difficult to separate the chaff from the grain, to distinguish harmless variations from disease-causing mutations. We were able to use a new process to screen variants in one candidate gene that has been linked to autism, and figure out how they might contribute to the disorder.”

An estimated one in 88 children in the United States is affected by autism spectrum disorders, a group of neurological development conditions marked by varying degrees of social, communication and behavioral problems. Scientists for years have looked for the biological roots of the problem using tools such as genome-wide association studies and gene-linkage analysis, which crunch genetic and health data from thousands of people in an effort to pinpoint disease-causing genetic variants. But while such techniques have turned up a number of gene mutations that may be linked to autism, none of them appear in more than 1 percent of people with the condition. With numbers that low, researchers need a way to screen variants in order to make a definitive link, Rao says.

For the new study, Rao and her collaborators focused on NHE9, which other researchers had flagged as a suspect in attention-deficit hyperactivity disorder, addiction and epilepsy as well as autism spectrum disorders. The gene was already known to be involved in transporting hydrogen, sodium and potassium ions in and out of cellular compartments called endosomes, and the team wondered how this function might be related to neurological conditions.

Rao’s collaborators at Tel Aviv University and Technion-Israel Institute of Technology constructed a computer model of the NHE9 protein based on previous research on a distant relative in bacteria. They then used the model to predict how autism-linked variants in the NHE9 gene would affect the protein’s shape and function. Some of them were predicted to cause dramatic changes, while other changes appeared to be more subtle.

Rao’s team next tested how these variant forms of NHE9 would affect a relatively simple organism often used in genetic studies: yeast. “Using yeast to screen the function of variants was a quick, easy and inexpensive way of figuring out which were worth further study, and which we could ignore because they didn’t have any effect,” Rao says. To do that, the team engineered the yeast form of NHE9 to have the variants seen in autistic people.

For those mutations that did have a detectable effect on the yeast, the team moved on to a third and more challenging step, in mouse brains. They homed in on astrocytes, a type of brain cell that clears the signaling molecule glutamate out of the way after it has performed its job of delivering a message across a synapse between two nerve cells. Using lab-grown mouse astrocytes with variant forms of NHE9, the researchers found a change in the pH (acidity) inside cellular compartments called endosomes, which in turn altered the ability of cells to take up glutamate. Because endosomes are the vehicles that deliver cargo essential for communication between brain cells, changing their pH alters traffic to and from the cell surface, which could affect learning and memory, Rao says. “Elevated glutamate levels are known to trigger seizures, perhaps explaining why autistic patients with mutations in NHE9 and related genes also have seizures,” she notes.

Rao and her team hope that pinpointing the importance of this trafficking mechanism in autism spectrum disorders may lead to the development of new drugs for autism that alter endosomal pH. As the use of genomic data becomes increasingly commonplace in the future, the step-wise strategy devised by her team can be used to screen gene variants and identify at-risk patients, she says.

(Source: hopkinsmedicine.org)

Activating a mother’s immune system during her pregnancy disrupts the development of neural cells in the brain of her offspring and damages the cells’ ability to transmit signals and communicate with one another, researchers with the UC Davis Center for Neuroscience and Department of Neurology have found. They said the finding suggests how maternal viral infection might increase the risk of having a child with autism spectrum disorder or schizophrenia.

The research, “MHCI Requires MEF2 Transcription Factors to Negatively Regulate Synapse Density during Development and in Disease,” is published in the Journal of Neuroscience.

The study’s senior author is Kimberley McAllister, professor in the Center for Neuroscience with appointments in the departments of Neurology and Neurobiology, Physiology and Behavior, and a researcher with the UC Davis MIND Institute.

“This is the first evidence that neurons in the developing brain of newborn offspring are altered by maternal immune activation,” McAllister said. “Until now, very little has been known about how maternal immune activation leads to autism spectrum disorder and schizophrenia-like pathophysiology and behaviors in the offspring.”

The study was conducted in mice and rats and compared the brains of the offspring of rodents whose immune systems had been activated and those of animals whose immune systems had not been activated. The pups of animals that were exposed to viral infection had much higher brain levels of immune molecules known as the major histocompatibility complex I (MHCI) molecules.

“This is the first evidence that MHCI levels on the surface of young cortical neurons in offspring are altered by maternal immune activation,” McAllister said.

The researchers found that the high MHCI levels impaired the ability of the neurons from the newborn mice’s brains to form synapses, the tiny gaps separating brain cells through which signals are transmitted. Earlier research has suggested that ASD and schizophrenia may be caused by changes in the development of connections in the brain, especially the cerebral cortex.

The researchers experimentally reduced MHCI to normal levels in neurons from offspring following maternal immune activation.

“Remarkably, synapse density returned to normal levels in those neurons,” McAllister said.

“These results indicate that maternal immune activation does indeed alter connectivity during prenatal development, causing a profound deficit in the ability of cortical neurons to form synapses that is caused by changes in levels of MHCI on the neurons,” she said.

MHCI did not work alone to limit the development of synapses. In a series of experiments, the UC Davis researchers determined that MHCI interacted with calcineurin and myocyte enhancer factor-2 (Mef2), a protein that is a critical determinant of neuronal specialization.

MHCI, calcineurin and Mef2 form a biological signaling pathway that had not been previously identified. McAllister’s team showed that in the offspring of the maternal immune activation mothers, this novel signaling pathway was much more active than it was in the offspring of non-MIA animals.

“This finding provides a potential mechanism linking maternal immune activation to disease-linked behaviors,” McAllister said.

It also is a mechanism that may help McAllister and other scientists to develop diagnostic tests and eventually therapies to improve the lives of individuals with these neurodevelopmental disorders.

(Source: ucdmc.ucdavis.edu)

UC Davis MIND Institute research finds rigorous evaluations are needed to accurately diagnose autism in children with 22q11.2 deletion syndrome

Children with a genetic disorder called 22q11.2 deletion syndrome, who frequently are believed to also have autism, often may be misidentified because the social impairments associated with their developmental delay may mimic the features of autism, a study by researchers with the UC Davis MIND Institute suggests.

The study is the first to examine autism in children with chromosome 22q11.2 deletion syndrome, in whom the prevalence of autism has been reported at between 20 and 50 percent, using rigorous gold-standard diagnostic criteria. The research found that none of the children with 22q11.2 deletion syndrome “met strict diagnostic criteria” for autism.

The researchers said the finding is important because treatments designed for children with autism, such as widely used discrete-trial training methods, may exacerbate the anxiety that is commonplace among the population.

Rather, evaluations should be performed to assess autism and guide the selection of appropriate therapies based on the children’s symptoms, such as language and communication delay, the researchers said. The study, “Social impairments in Chromosome 22q11.2 Deletion Syndrome (22q11.2DS): Autism Spectrum Disorder or a different Endophenotype?” is published online today in Springer’s Journal of Autism and Developmental Disorders.

A high prevalence of autism spectrum disorder has been reported in children with 22q11.2 deletion syndrome – as high as 50 percent based on parent-report measures. Children diagnosed with 22q11.2 deletion syndrome – or 22q – may experience mild to severe cardiac anomalies, weakened immune systems and malformations of the head and neck and the roof of the mouth, or palate. They also experience developmental delay, with IQs in the borderline-to-low-average range. They characteristically experience significant anxiety and appear socially awkward.

“The results of our study show that of the children involved in our study no child actually met strict diagnostic criteria for an autism spectrum disorder,” said Kathleen Angkustsiri, study lead author and assistant professor of developmental-behavioral pediatrics at the MIND Institute.

“This is very important because the literature cites rates of anywhere from 20 to 50 percent of children with the disorder also have an autism spectrum disorder. Our findings lead us to question whether this is the correct label for these children who clearly have social impairments. We need to find out what interventions are most appropriate for their difficulties.”

The disorder’s name also describes its location on the 22^nd chromosome as well as the nature of the genetic mutation, which is associated with a variety of anatomical and intellectual deficits.  It has previously been known as Velocardiofacial Syndrome and Di George Syndrome, for the pediatric endocrinologist who described it in the 1960s.

The risk of 22q is about 1 in 2000 in the general population. The condition is seen in individuals of all backgrounds. Notably, people with 22q are at significantly heightened risk of developing mental-health disorders in adolescence and young adulthood. A person with 22q has a 30 times greater risk of developing schizophrenia than individuals in the general population.

“Because of the high rates of psychiatric disorders in childhood and adulthood, 22q is a very special population for prospective study looking at what’s happening throughout childhood that might either increase risk or provide protection against some of the later developing serious psychiatric illnesses, such as schizophrenia, that are associated with the disorder,” said Tony J. Simon, professor of psychiatry and behavioral sciences and director of the chromosome 22q11.2 deletion program at the MIND Institute.

The study was conducted among individuals recruited through the website of the Cognitive Analysis and Brain Imaging Laboratory (CABIL), which Simon directs. Simon and Angkustsiri said that the parents of children with 22q deletion syndrome often had commented that their children “seemed different” from other children with autism diagnoses, but that they hadn’t discovered a better diagnosis.

The clinical impression of the MIND Institute’s 22q deletion syndrome team, which includes psychologists Ingrid Leckliter and Janice Enriquez, was that the children were experiencing significant social impairments, but their presentation diverged from that of children with autism. To determine whether the children met the criteria for classic autism, they decided to test a subset of the children recruited from participants in a larger study of neurocognitive functioning, based on stringent methods and using multiple testing instruments.

The researchers selected 29 children –16 boys and 13 girls – for additional scrutiny, administering two tests. The Autism Diagnostic Observation Schedule (ADOS), a gold-standard assessment for autism, was administered to the children. The Social Communication Questionnaire (SCQ), a 40-question parent screening tool for communication and social functioning based on the gold-standard Autism Diagnostic Interview-Revised, was administered to their parents.

Typically, a diagnosis of autism spectrum disorder requires elevated scores on both a parent report measure, such as the SCQ, and a directly administered assessment such as the ADOS.  Prior studies of autism in chromosome 22q11.2 deletion syndrome have only used parent report measures.

Only five of the 29 children had scores in the elevated range on the ADOS diagnostic tool. Four of the five had significant anxiety. Only two – 7 percent – had SCQ scores above the cut off. No child had both SCQ and ADOS scores in the relevant ranges that would lead to an ASD diagnosis.

 “Over the years, a number of children came to us as part of the research or the clinical assessments that we perform, and their parents told us that they had an autism spectrum diagnosis. It’s quite clear that children with the disorder do have social impairments,” Simon said. “But it did seem to us that they did not have a classic case of autism spectrum disorder. They often have very high levels of social motivation. They get a lot of pleasure from social interaction, and they’re quite socially skilled.”

Simon said that the team also noted that the children’s social deficits might be more a function of their developmental delay and intellectual disability than autism.

“If you put them with their younger siblings’ friends they function very well in a social setting,” Simon continued, “and they interact well with an adult who accommodates their expectations for social interaction.”

Angkustsiri said that further study is needed to assess more appropriate treatments for children with 22q, such as improving their communication skills, treating their anxiety, helping them to remain focused and on task.

 “There are a variety of different avenues that might be pursued rather than treatments that are designed to treat children with autism,” Angkustsiri said. “There are readily available, evidence-based treatments that may be more appropriate to help maximize these children’s potential.”

(Source: ucdmc.ucdavis.edu)

Researchers at the Stanford University School of Medicine have shown that oxytocin — often referred to as “the love hormone” because of its importance in the formation and maintenance of strong mother-child and sexual attachments — is involved in a broader range of social interactions than previously understood.

The discovery may have implications for neurological disorders such as autism, as well as for scientific conceptions of our evolutionary heritage.

Scientists estimate that the advent of social living preceded the emergence of pair living by 35 million years. The new study suggests that oxytocin’s role in one-on-one bonding probably evolved from an existing, broader affinity for group living.

Oxytocin is the focus of intense scrutiny for its apparent roles in establishing trust between people, and has been administered to children with autism spectrum disorders in clinical trials. The new study, published Sept. 12 in Nature, pinpoints a unique way in which oxytocin alters activity in a part of the brain that is crucial to experiencing the pleasant sensation neuroscientists call “reward.” The findings not only provide validity for ongoing trials of oxytocin in autistic patients, but also suggest possible new treatments for neuropsychiatric conditions in which social activity is impaired.

"People with autism-spectrum disorders may not experience the normal reward the rest of us all get from being with our friends," said Robert Malenka, MD, PhD, the study’s senior author. "For them, social interactions can be downright painful. So we asked, what in the brain makes you enjoy hanging out with your buddies?"

Some genetic evidence suggests the awkward social interaction that is a hallmark of autism-spectrum disorders may be at least in part oxytocin-related. Certain variations in the gene that encodes the oxytocin receptor — a cell-surface protein that senses the substance’s presence — are associated with increased autism risk.

Malenka, the Nancy Friend Pritzker Professor in Psychiatry and Behavioral Sciences, has spent the better part of two decades studying the reward system — a network of interconnected brain regions responsible for our sensation of pleasure in response to a variety of activities such as finding or eating food when we’re hungry, sleeping when we’re tired, having sex or acquiring a mate, or, in a pathological twist, taking addictive drugs. The reward system has evolved to reinforce behaviors that promote our survival, he said.

For this study, Malenka and lead author Gül Dölen, MD, PhD, a postdoctoral scholar in his group with over 10 years of autism-research expertise, teamed up to untangle the complicated neurophysiological underpinnings of oxytocin’s role in social interactions. They focused on biochemical events taking place in a brain region called the nucleus accumbens, known for its centrality to the reward system.

In the 1970s, biologists learned that in prairie voles, which mate for life, the nucleus accumbens is replete with oxytocin receptors. Disrupting the binding of oxytocin to these receptors impaired prairie voles’ monogamous behavior. In many other species that are not monogamous by nature, such as mountain voles and common mice, the nucleus accumbens appeared to lack those receptors.

"From this observation sprang a dogma that pair bonding is a special type of social behavior tied to the presence of oxytocin receptors in the nucleus accumbens. But what’s driving the more common group behaviors that all mammals engage in — cooperation, altruism or just playing around — remained mysterious, since these oxytocin receptors were supposedly absent in the nucleus accumbens of most social animals," said Dölen.

The new discovery shows that mice do indeed have oxytocin receptors at a key location in the nucleus accumbens and, importantly, that blocking oxytocin’s activity there significantly diminishes these animals’ appetite for socializing. Dölen, Malenka and their Stanford colleagues also identified, for the first time, the nerve tract that secretes oxytocin in the region, and they pinpointed the effects of oxytocin release on other nerve tracts projecting to this area.

Mice can squeak, but they can’t talk, Malenka noted. “You can’t ask a mouse, ‘Hey, did hanging out with your buddies a while ago make you happier?’” So, to explore the social-interaction effects of oxytocin activity in the nucleus accumbens, the investigators used a standard measure called the conditioned place preference test.

"It’s very simple," Malenka said. "You like to hang out in places where you had fun, and avoid places where you didn’t. We give the mice a ‘house’ made of two rooms separated by a door they can walk through at any time. But first, we let them spend 24 hours in one room with their littermates, followed by 24 hours in the other room all by themselves. On the third day we put the two rooms together to make the house, give them complete freedom to go back and forth through the door and log the amount of time they spend in each room."

Mice normally prefer to spend time in the room that reminds them of the good times they enjoyed in the company of their buddies. But that preference vanished when oxytocin activity in their nucleus accumbens was blocked. Interestingly, only social activity appeared to be affected. There was no difference, for example, in the mice’s general propensity to move around. And when the researchers trained the mice to prefer one room over the other by giving them cocaine (which mice love) only when they went into one room, blocking oxytocin activity didn’t stop the mice from picking the cocaine den.

In an extensive series of sophisticated, highly technical experiments, Dölen, Malenka and their teammates located the oxytocin receptors in the murine nucleus accumbens. These receptors lie not on nucleus accumbens nerve cells that carry signals forward to numerous other reward-system nodes but, instead, at the tips of nerve cells forming a tract from a brain region called the dorsal Raphe, which projects to the nucleus accumbens. The dorsal Raphe secretes another important substance, serotonin, triggering changes in nucleus accumbens activity. In fact, popular antidepressants such as Prozac, Paxil and Zoloft belong to a class of drugs called serotonin-reuptake inhibitors that increase available amounts of serotonin in brain regions, including the nucleus accumbens.

As the Stanford team found, oxytocin acting at the nucleus accumbens wasn’t simply squirted into general circulation, as hormones typically are, but was secreted at this spot by another nerve tract originating in the hypothalamus, a multifunction midbrain structure. Oxytocin released by this tract binds to receptors on the dorsal Raphe projections to the nucleus accumbens, in turn liberating serotonin in this key node of the brain’s reward circuitry. The serotonin causes changes in the activity of yet other nerve tracts terminating at the nucleus accumbens, ultimately resulting in altered nucleus accumbens activity — and a happy feeling.

"There are at least 14 different subtypes of serotonin receptor," said Dölen. "We’ve identified one in particular as being important for social reward. Drugs that selectively act on this receptor aren’t clinically available yet, but our study may encourage researchers to start looking at drugs that target it for the treatment of diseases such as autism, where social interactions are impaired."

Malenka and Dölen said they think their findings in mice are highly likely to generalize to humans because the brain’s reward circuitry has been so carefully conserved over the course of hundreds of millions of years of evolution. This extensive cross-species similarity probably stems from pleasure’s absolutely essential role in reinforcing behavior likely to boost an individual’s chance of survival and procreation.

(Source: med.stanford.edu)

A new study in Biological Psychiatry explores the influence of oxytocin

Difficulty in registering and responding to the facial expressions of other people is a hallmark of autism spectrum disorder (ASD). Relatedly, functional imaging studies have shown that individuals with ASD display altered brain activations when processing facial images.

The hormone oxytocin plays a vital role in the social interactions of both animals and humans. In fact, multiple studies conducted with healthy volunteers have provided evidence for beneficial effects of oxytocin in terms of increased trust, improved emotion recognition, and preference for social stimuli.

This combination of scientific work led German researchers to hypothesize about the influence of oxytocin in ASD. Dr. Gregor Domes, from the University of Freiburg and first author of the new study, explained: “In the present study, we were interested in the question of whether a single dose of oxytocin would change brain responses to social compared to non-social stimuli in individuals with autism spectrum disorder.”

They found that oxytocin did show an effect on social processing in the individuals with ASD, “suggesting that oxytocin may help to treat a basic brain function that goes awry in autism spectrum disorders,” commented Dr. John Krystal, Editor of Biological Psychiatry.

To conduct this study, they recruited fourteen individuals with ASD and fourteen control volunteers, all of whom completed a face- and house-matching task while undergoing imaging scans. Each participant completed this task and scanning procedure twice, once after receiving a nasal spray containing oxytocin and once after receiving a nasal spray containing placebo. The order of the sprays was randomized, and the tests were administered one week apart.

Using two sets of stimuli in the matching task, one of faces and one of houses, allowed the researchers to not only compare the effects of the oxytocin and placebo administrations, but also allowed them to discriminate findings between specific effects to only social stimuli and non-specific effects to more general brain processing.

What they found was intriguing. The data indicate that oxytocin specifically increases responses of the amygdala to social stimuli in individuals with ASD. The amygdala, the authors explain, “has been associated with processing of emotional stimuli, threat-related stimuli, face processing, and vigilance for salient stimuli”.

This finding suggests oxytocin might promote the salience of social stimuli in ASD. Increased salience of social stimuli might support behavioral training of social skills in ASD.

These data support the idea that oxytocin may be a promising approach in the treatment of ASD and could stimulate further research, even clinical trials, on the exploration of oxytocin as an add-on treatment for individuals with autism spectrum disorder.

(Source: alphagalileo.org)