New mutations implicated in half of autism cases

news@nature.com ^ | 24 July 2007 | Heidi Ledford

[neverdem]

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Published online: 24 July 2007; | doi:10.1038/news070723-1

New mutations implicated in half of autism cases

Disorder linked to genetic differences between parent and offspring.

Heidi Ledford

Autistic children display a wide range of different symptoms.HENNY ALLIS / SCIENCE PHOTO LIBRARY

Half of all cases of male autism may be caused by spontaneous genetic mutations, say researchers who have studied the genetic patterns of the condition. Offspring who inherit such mutations are at a greater risk of having an autistic child themselves.

Autistic people have difficulty relating socially with others and tend to focus obsessively on a narrow set of interests. Three to six out of every 1,000 people are expected to have the condition; its cause is unknown but there is thought to be a strong genetic component.

"That genetics plays a major role in autism has been obvious now for 20 years or more," says Isabelle Rapin, a neurologist at Albert Einstein College of Medicine in New York, who was not affiliated with the study. "The evidence for genetics is not controversial."

But determining how genes affect autism has been difficult. Autism is a complex disease with a wide range of symptoms and severity. It also affects four times more males than females, for unknown reasons.

Spontaneous mutation

Earlier this year, a genome-wide scan linked some cases of autism with mutations in the number of copies of certain genes. Ten per cent of autistic patients had copy-number mutations that were not present in either parent, showing that the mutations were spontaneous¹.

But Michael Wigler, a geneticist at Cold Spring Harbor Laboratory in New York and a lead author on the study, says that the study probably missed some copy-number mutations. "We were sure that 10% was an underestimate," he says.

So Wigler and his colleagues turned to a database containing pedigrees of families with two or more autistic children and asked: if the family's first two children were autistic, what were the chances that the third was autistic as well?

In 86 families with two autistic children and a third, male child, 42 of the third-born children showed autistic symptoms, the researchers report in Proceedings of the National Academies of Sciences².

This suggests that parents had a one-in-two chance of passing on a mutation to their offspring, matching a dominant inheritance pattern. Another database gave the same result.

Handed down

Using mathematical models, Wigler's team found that the simplest way to describe the patterns of autism inheritance was to divide parents into two risk classes: those who carry a pre-existing autism-causing mutation, and those who do not.

The models suggest that about half of autistic children are born to parents with no previous genetic predisposition to autism, suggesting that the cases are caused by spontaneous mutations.

Older mothers, who are more likely to have autistic children, could fall into this class, notes Wigler. Such mothers' eggs have had more time to accumulate mutations.

Once those spontaneous mutations have been passed on, the offspring — particularly women, who can carry the mutation without showing symptoms — have a high risk of having an autistic child. Males with the mutation would also bear this risk, but are also likely to be autistic and therefore less likely to have children.

The researchers' model suggested that about a quarter of autistic children have inherited a copy-number mutation from their parents.

"It's a new way of looking at the data," says Rapin. Future studies using data from other family members are needed to further test the new models, she says. Other factors, such as complications during pregnancy, and the influence of multiple genes, may also be important in causing autism.

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References

1. Sebat, J. et al. Science 316, 445-449 (2007). | Article | PubMed | ISI | ChemPort |
2. Zhao, X. et al. Proc. Natl Acad. Sci. USA doi: 10.1073/pnas.0705803104 (2007).

[darkangel82]

It seems like everyone here on FR thinks Big Pharma can do no wrong

No, not all of us, only the corporatists.

[Scotsman will be Free]

All dryers are portals to the fourth dimension.

[Vinnie]

IMHO, I think the increased prevalence of autistic spectrum disorder is due to having more specific diagnostic criteria, i.e. in the past many would have been diagnosed as mentally retarded, in addition to those now diagnosed with pervasive developmental disorder and Asperger's syndrome.

Physical and mentally handicapped kids are much more visible than years ago.
When I was a student, 50's, there was a school devoted to these kids. Separate buses, separate plant.
Today they are in the same physical plant with other students.
They may be in separate classrooms but they are much more visible.

[Incorrigible]

Do you know if the mother has an autoimmune disease? (ie, Multiple Sclerosis (MS), Lupus, Graves disease, etc)

[Hot Tabasco]

Your sister is doing him no favors

I know that. My brother-in-law is a PHD psychologist and of course knows fully well the scope of the problem. Unfortunately, there has been a lot of friction between my sister and her daughter-in-law to the point that my sister and brother-in-law have backed out of this only to be able to maintain a sense of normalcy between them and their son and his family........

It is very upsetting to say the least.......

[nmh]

One of them had something - nothing you mentioned and still both of their sons were autistic.

I have M.S., Graves and had a child, without chemical at 43 and she was perfectly normal. Oh, I was told she’d have Downs Syndrome and be retarded. She’s normal and exceptionally bright.

They really don’t know what causes this - they’re groping at straws.

[Conservativegreatgrandma]

Aspergers describes my grandson who was diagnosed as autistic as a youngster. He's now 17 and doing very well. He's preparing for college and had a perfect ACT math score. He's now at an engineering program at a college for juniors. He loves it.

He's programming Python for a video game. Does that make sense? I hope I told it right.

[Conservativegreatgrandma]

I swear there’s a digestive component to autism.

[MarMema]

Always check your backside in the mirror before leaving for work....

rofl!!

[AppyPappy]

Yeah Python is a programming language

[Conservativegreatgrandma]

I asked him why he would want to program a python? He’s a great kid and has brought our family much joy and extreme pleasure with his accomplishments. He’s a math whiz and has won many math competitions and also aced math on the ACT.

[Question_Assumptions]

What's tweeking our DNA to mutate?

It can do that all by itself. The copying isn't always perfect. But if the question is, why dis this becoming more common now, I think the answer could be, in part, that women are waiting until later in life to have children. The older the mother (and some research suggests, the father), the higher the risk of genetic problems like Down's Syndrome. It would seem to make sense sense that other issues are occurring, too.