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Gene
mutation, key symptoms of autism appear to be linked
Gene
mutation, key symptoms of autism appear to be linked
Date:
April 25,
2014
Source:
Scripps Research Institute
Summary:
Abnormal brain growth is associated with autism
spectrum disorder -- this scientists know. However, the relationship between
the two has not been well understood. Now, research has 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.
.........................
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.”
“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.”
Story
Source:
The above
story is based on materials
provided by Scripps
Research Institute. Note: Materials may be edited for content and
length.
Journal
Reference:
- A. E. Clipperton-Allen, D. T. Page. Pten haploinsufficient mice show broad brain overgrowth but selective impairments in autism-relevant behavioral tests. Human Molecular Genetics, 2014; DOI: 10.1093/hmg/ddu057
Cite This
Page:
Scripps Research Institute.
"Gene mutation, key symptoms of autism appear to be linked."
ScienceDaily. ScienceDaily, 25 April 2014.
<www.sciencedaily.com/releases/2014/04/140425091843.htm