Scientists have known that abnormal brain growth is associated with autism spectrum disorder. However, the relationship between the two has not been well understood.
Now, scientists from the Florida campus of The Scripps Research Institute (TSRI) have shown that mutations in a specific gene that is disrupted in some individuals with autism results in too much growth throughout the brain, and yet surprisingly specific problems in social interactions, at least in mouse models that mimic this risk factor in humans.
“What was striking is that these were basically normal animals in terms of behavior, but there were consistent deficits in tests of social interaction and recognition—which approximate a major symptom of autism,” said Damon Page, a TSRI biologist who led the study. “This suggests that when most parts of the brain are overgrown, the brain somehow adapts to it with minimal effects on behavior in general. However, brain circuits relevant to social behavior are more vulnerable or less able to tolerate this overgrowth.”
The study, which focuses on the gene phosphatase and tensin homolog (PTEN), was recently published online ahead of print by the journal Human Molecular Genetics.
Autism spectrum disorder is a neurodevelopmental disorder involving a range of symptoms and disabilities involving social deficits and communication difficulties, repetitive behaviors and interests, and sometimes cognitive delays. The disorder affects in approximately one percent of the population; some 80 percent of those diagnosed are male.
In a previous study, Page and colleagues found that mutations in Pten causes increased brain size and social deficits, with both symptoms being exacerbated by a second “hit” to a gene that regulates levels of the neurotransmitter serotonin in the brain. In the new study, the TSRI team set out to explore whether mutations in Pten result in widespread or localized overgrowth within the brain, and whether changes in brain growth are associated with broad or selective deficits in tests of autism-relevant behaviors in genetically altered mice. The team tested mice for autism spectrum disorder-related behaviors including mood, anxiety, intellectual, and circadian rhythm and/or sleep abnormalities.
The researchers found that Pten mutant mice showed altered social behavior, but few other changes—a more subtle change than would have been predicted given broad expression and critical cellular function of the gene.
Intriguingly, some of the more subtle impairments were sex-specific. In addition to social impairments, males with the mutated gene showed abnormalities related to repetitive behavior and mood/anxiety, while females exhibited additional circadian activity and emotional learning problems.
The results raise the question of how mutations in PTEN, a general regulator of growth, can have relatively selective effects on behavior and cognitive development. One idea is that PTEN mutations may desynchronize the normal pattern of growth in key cell types—the study points to dopamine neurons—that are relevant for social behavior.
“Timing is everything,” Page said. “Connections have to form in the right place at the right time for circuits to develop normally. Circuitry involved in social behavior may turn out to be particularly vulnerable to the effects of poorly coordinated growth.”
Furthermore I would like to provide possible answers to questions asked by the previous bloggers. Studies show that the PTEN gene is located on the X chromosome and whilst boys inherit this gene from their mothers only, girls inherit this gene from both parents. The X chromosome which girls inherit from their fathers are believed to contain an imprinted gene which protects the girl from Autism unlike the boy who does not receive a X chromosome from his father.
Also because the symptoms for Autism vary from male to female the tests for diagnosis of Autism more focused on the symptoms of boys which results in underdiagnosed females with this disorder.
Scientists are not yet sure but I believe both of these could be answers to why Males are more likely to be diagnosed with Autism than females.
To me this was a very insightful blog. It was amazing to learn that our brains have the ability to adapt when overgrown and that mostly with minimal effects. It was also interesting to learn that brain circuits relevant to social behavior is actually more vulnerable to a mutated gene(PTEN) than other brain circuits. Also interestingly enough I learned that the percentage of people in the world who have the Autism disorder is quite low and that men are more vulnerable to it than women. Autism is a very peculiar disorder because the symptoms differ from male to female. Finding out that Autism is caused by a mutated gene(PTEN) and now knowing exactly what the function of the PTEN gene is and how mutations in this gene influences the brain this disorder has become much more understandable to me.
The information that this article provides is, indeed, quite interesting. It is worth pointing out that many researchers believe that in some instances autism can be caused by a mutated gene inherited by the infant from it biological parents. Hopefully with advances in biomedical technology in the future we should be able to identify these mutant genes during the early stages of gestation where, as an alternative to abortion, scientists could use genetic modification to displace these unwanted genes with the non-mutant ones (I believe this procedure has been done successfully on more simple organisms). Slowly, but surely, the genetic factors causing autism will be eradicated from the human gene pool.
The article has interesting new discoveries on autism in which people can get a better understanding of the disorder. the more people understand the science behind such a disorder that even though there is no cure there could be better treatment of people suffering with autism. The lack of information on the subject had previously lead to the mistreatment of autistic patients. However is it not possible that people with autism also arise from childhood events that had brought on a reaction, as is with the case of people with psychological disorder i.e schizophrenia?
Autism is a field of study that has interested many scientists as it is still not fully understood. As shown in the article there are more discoveries being made with regards to autism. The gene mutations are a possible cause of autism however, it is has not been proven to be the only cause of autism. is it possible to test for other causes for autism? Furthermore, does the differences between males and females cause inconsistencies in any of the research previously conducted?
This was a fascinating article to read as connections between autism and the mutations in genes helps to build our understanding of autism and how the brain functions. It was interesting to know that the disorder affects more males than females and that the affects are different for the different sexes.But why is this? and what causes these mutations on the Pten ?
This new information regarding autism and its link to mutations is very intriguing, and I believe it will lead to many discoveries within this field. However, why is it that this disorder affects males more than it does females? This article discusses the PTEN mutations, is it known whether these mutations are directly caused by a specific mutagen or are they random mutations which are heritable?