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A leading genetic cause of autism: Fragile X syndrome

Chriza28

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Searched "Fragile X syndrome’s link to autism, explained" -No results found.

If you know someone with a family history of autism,

this may be critical information for them or anyone planning a family.

Listen to this story:

Fragile X syndrome is a leading genetic cause of autism. About one in three people with the syndrome also has autism. But even those who do not have autism often share certain autistic traits, such as avoidance of eye contact and difficulties in social situations. Mutations in the gene FMR1, which cause fragile X syndrome, account for up to 5 percent of autism cases.

For these reasons, research on fragile X can provide insights into the biology of autism and its treatment. Here is what scientists know about the mechanisms that underlie fragile X and some research angles they are pursuing.

What is fragile X syndrome?
Fragile X syndrome is the most common cause of intellectual disability. It affects roughly 1 in 4,000 men and about half as many women1. People with the syndrome also tend to have unusual physical features, such as a long face, large ears and flat feet. Some men have large testes, and some people with the condition have seizures.

What is the relationship between fragile X syndrome and autism?
Almost 50 percent of men and 16 percent of women with fragile X also have autism, according to the U.S. Centers for Disease Control and Prevention. Other studies have hinted that up to 90 percent of men with fragile X have some autism traits, such as a tendency to avoid eye contact2. Studies indicate that these traits may present differently in the two conditions. For instance, people with fragile X may show a few classic repetitive behaviors, such as hand-flapping, whereas autistic people typically have a broad range of repetitive behaviors, restricted interests or both. People with fragile X and those with autism may also have divergent developmental trajectories: For instance, social problems may worsen more, or more rapidly, in autistic people than in those with both autism and fragile X.

What causes fragile X?
In most cases, the syndrome is caused by a mutation in FMR1, located on the X chromosome. People with fragile X have more than 200 repetitions of a sequence of three nucleotides, ‘CGG,’ at the start of the gene; typical people have 54 or fewer of these repeats. Under a microscope, this CGG expansion can cause the tip of the X chromosome to appear ‘fragile.’

The expanded repeats can silence the production of a protein called FMRP. This protein serves critical functions, such as controlling the production of proteins at synapses, the junctions between neurons.

The leading theory of fragile X holds that when FMRP is missing, protein synthesis can run rampant and disrupt cognitive processes. A study published last month, however, has complicated scientists’ understanding of the syndrome: It hints that loss of FMRP instead causes a dearth of proteins.

What is the fragile X syndrome ‘premutation’?
The fragile X ‘premutation’ is defined as having 55 to 200 CGG repeats in FMR1. The premutation tamps down production of FMRP but does not silence it. Because premutation carriers may not show outward signs, the prevalence of premutations is unknown. Estimates range from 1 in 148 to 1 in 291 in women and from 1 in 290 men to 1 in 855 in men in the United States.

Some women with the premutation develop a condition called fragile X-associated primary ovarian insufficiency, which can trigger early menopause. Both men and women with the premutation may develop a condition called fragile X-associated tremor/ataxia syndrome, which causes tremors and cognitive problems. The risk of developing this condition increases with age: Estimates suggest 30 percent of affected men and 8 to 16.5 percent of affected women over age 50 have it1.

The repeats of the premutation can sometimes expand in future generations to the full syndrome. The more repeats in the mother’s premutation, the greater the chance the child will have a full mutation.

Some people have between 45 and 54 CGG repeats — a so-called ‘gray zone’ mutation. Little is known about the effects of this mutation, although evidence suggests it can lead to some features of fragile X-associated tremor/ataxia syndrome.

Are there animal models available to study fragile X?
Researchers have developed mouse and rat models of fragile X syndrome by deleting FMR1. The brains of these mice respond abnormally to social stimuli, such as meeting a new mouse. The mutant mice also show alterations in a brain circuit involving the prefrontal cortex, which plays a role in social cognition.

Whether insights from the mice apply to people with the condition is unclear. The behaviors seen in mice that lack FMR1 are often inconsistent — and in many cases do not resemble those in people. For instance, the mutant mice do not show cognitive problems, one of the core features of fragile X. An animal model that faithfully mimics the syndrome would help researchers test treatments and trace the syndrome’s origins.

Are there treatments for fragile X syndrome?
A range of available behavioral therapies may improve speech and language abilities in people with fragile X. But there are no approved drugs for the syndrome.

Researchers are investigating many candidate drugs, including several that block a protein called mGluR5. Some of the candidates, such as arbaclofen and mavoglurant, have been shown to restore protein production and ease problems with learning and memory in the mutant mice. But none of the drugs has fared well in clinical trials.

That may be because the trials used the wrong markers to measure the drugs’ effectiveness. Or it may because the trials involved adolescents and adults, whose brains may no longer respond to intervention. One team is testing mavoglurant in young children and using a test of language learning to measure its effectiveness. They plan to pair the drug with an intensive language intervention.

Other teams are testing a drug called lovastatin, which is used to treat high cholesterol levels and has been shown to reduce seizures in fragile X mice. Researchers are also testing a drug that targets the enzyme PDE4D and seems to improve social behaviors in the mutant mice3.

What are the next steps for the field?
Researchers are pushing to develop good outcome measures for clinical trials and to investigate promising drug candidates. Other efforts aim to clarify the functions of FMRP or to repair the mutation. In a March study, for example, researchers used a gene-editing tool to remove chemical tags from CGG repeats in cells from a person with fragile X. The treatment restored FMRP expression to 90 percent of normal levels.

REFERENCES:​

  1. Seltzer M.M. et al. Am. J. Med. Genet. B. Neuropsychiatr. Genet.159B, 589-597 (2012) PubMed
  2. Hernandez R.N. et al. Am. J. Med. Genet. A.149A, 1125-1137 (2009) PubMed
  3. Gurney M.E. et al.Sci. Rep.7, 14653 (2017) PubMed




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AfroSoul

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bµllsh!t , anytime scientists dont know the origin of a illness , they call it " genetic" . Autism rate has exploded by 300% since the 50's, why would the " Fragile Syndrome" exist only from that era ? Before the 50's there were hardly any autistics children ,same thing with Cancer , Diabete and every other Civilisation illnesses that have appeared with industrial food , polution , Vaccine and chemical Medecine .Fragile X Syndrome , my ass !
 

Didyme

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bµllsh!t , anytime scientists dont know the origin of a illness , they call it " genetic" .
Did you not read the article? The answer to this is laid out repeatedly.
Fragile X syndrome is a leading genetic cause of autism. About one in three people with the syndrome also has autism.

Mutations in the gene FMR1, which cause fragile X syndrome, account for up to 5 percent of autism cases.

The fragile X ‘premutation’ is defined as having 55 to 200 CGG repeats in FMR1.
That's not an unknown origin. That's a specific genetic error.
Autism rate has exploded by 300% since the 50's, why would the " Fragile Syndrome" exist only from that era ? Before the 50's there were hardly any autistics children
We only started tracking data on autism prevalence in 2000. So these stats you cite, 300% and hardly any, are in no way backed by any real data.

Now, has the rate increased?

Yes.

It used to be that only those who were severely autistic were diagnosed. Now autism was broadened to include its milder forms, more children have been able to be diagnosed and given life-changing early childhood intervention. Much better than the days in which such children might be sent away, or pushed to the fringes of society without any resources.

Our awareness and education has lead to increased diagnosis with better outcomes for children at every point within the spectrum.
 
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Chriza28

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bµllsh!t , anytime scientists dont know the origin of a illness , they call it " genetic" . Autism rate has exploded by 300% since the 50's, why would the " Fragile Syndrome" exist only from that era ? Before the 50's there were hardly any autistics children ,same thing with Cancer , Diabete and every other Civilisation illnesses that have appeared with industrial food , polution , Vaccine and chemical Medecine .Fragile X Syndrome , my ass !


Infographic: How the world’s population tripled in 70 years

1950 was 70 years ago and the population has increase by almost 200%. PLUS: science has now progressed immeasurably to the point we understand the power of diet, exercise and genetics.

70 years ago, children who were brain-wired differently were name-called insulting names and physically disciplined in class. Ignorance was rife.


An actor friend told me how he struggled in school and treated like a dunce by teachers. As an actor, "readings" (which actors do for auditions) were a nightmare. Yet, he was highly intelligent in every other aspect. My point here is that no one knew he had a genetic condition that caused his difficulty. There was a lot of ignorance back then.

Since the turn of the century, genetic research has provided increasing evidence supporting a genetic origin of dyslexia.

I am just using dyslexia as an example of how science and medicine hadn't progressed sufficiently back then. Dyslexia is of special interest to me because as a life-long reader who, as a child, read books for pleasure in more than one language, I just could not imagine life without being able to read with ease.


A big part of the reason I posted this is because for YEARS I kept hearing people fear-mongering over vaccinating their kids because autism had become such a big topic.

It is beyond bizarre to me that (going back about 10 years) even a nurse I know was crying over having had her (still) incredibly healthy only child vaccinated.

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LaBamba

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I wish that preconception genetic screening gained prevalence outside of couples needing fertility treatments. A solid carrier screening would avoid a lot of inherited genetic issues; I was just watching a clip from this new TLC show “The Blended Bunch” last night. 4 of a couples 7 children have a disorder that has a 95%+ chance of causing them to develop cancer in their teenage years or young adulthood. They got the gene from their dad who eventually died from cancer. Had he and his wife knew he had this disorder, they could’ve went the route of IVF with genetic testing to have their children or avoided having children altogether.

I also place blame with cheap insurance companies though who don’t want to pay for “unnecessary” testing (even though preventative medicine is always WAY cheaper than treatment).
 

Livingit88

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It's that old man sperm. Just because you can have kids in your 50s and over doesn't mean you should.
 

Sin Verguenza

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bµllsh!t , anytime scientists dont know the origin of a illness , they call it " genetic" . Autism rate has exploded by 300% since the 50's, why would the " Fragile Syndrome" exist only from that era ? Before the 50's there were hardly any autistics children ,same thing with Cancer , Diabete and every other Civilisation illnesses that have appeared with industrial food , polution , Vaccine and chemical Medecine .Fragile X Syndrome , my ass !
Maybe because they actually have a diagnosis for it now. Back in the days, those people would just be categorized as "simple"

Why do people think they are smarter than scientists?
 

Metaphysique

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It’s a common comorbidity, but not the sole cause of ASD. This isn’t particularly new. Two of my kids have HFA, which they get from their father, and I’m pretty sure he has an uncle on the spectrum as well. I had a great-aunt that many relatives started to suspect had autism throughout her life. Two of my cousins have kids with ASD — no connection to Fragile X Syndrome.
 

Vtg

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I wish that preconception genetic screening gained prevalence outside of couples needing fertility treatments. A solid carrier screening would avoid a lot of inherited genetic issues; I was just watching a clip from this new TLC show “The Blended Bunch” last night. 4 of a couples 7 children have a disorder that has a 95%+ chance of causing them to develop cancer in their teenage years or young adulthood. They got the gene from their dad who eventually died from cancer. Had he and his wife knew he had this disorder, they could’ve went the route of IVF with genetic testing to have their children or avoided having children altogether.

I also place blame with cheap insurance companies though who don’t want to pay for “unnecessary” testing (even though preventative medicine is always WAY cheaper than treatment).

disagree. even when people know, they still reproduce...
 

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