Autism has been a frustrating puzzle for geneticists. Searching for genes involved in the disorder, they have focused mainly on the 10% of cases that seem to be inherited. Now a group has made progress toward figuring out what goes wrong in the other 90%, the so-called sporadic cases.
Led by Jonathan Sebat of Cold Spring Harbor Laboratory in New York, the team looked at DNA from 264 families. Using a variety of techniques, the researchers scanned the genetic material for so-called copy number variants, in which relatively long stretches of DNA are lost or gained. Sebat and colleagues found these defects in about 1% of the 196 people without autism they tested. The rate was 10-fold higher among 112 sporadic cases (people who were the only ones in their families with autism). In contrast, copy number variants turned up in just 2% of 47 families with multiple cases of apparently inherited autism, the team reports today in Science. When the researchers further tested the families with a single case, they found that the parents did not have the mutation, suggesting that the mutations were not inherited but had arisen spontaneously in mom's egg or dad's sperm.
Sebat estimates that at least 15% of cases of autism and closely related disorders are due to these kinds of mutations. And he expects that fraction to rise considerably when the team continues the research on more families and with more sensitive DNA probes--work that will also help pin down the genes involved. "Increasing our resolution and sample size is going to give us a better idea of where the major players are," he says.
In the meantime, the finding could be useful for parents with an autistic child who worry that the disorder is inherited in their family and that future children will also be autistic. "If a [spontaneous] deletion is identified, the recurrence risk seems greatly reduced," says Linda Brzustowicz of Rutgers University in New Jersey.
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