THE first gene to be linked to autism may have been discovered by American
researchers. They think rare mutations in this gene can affect brain
development.
But even if their finding is confirmed, it seems the gene is involved in only
a small proportion of cases. Researchers believe there are at least a dozen
genes involved in autism. Family studies have revealed the rough location of
some of these genes, and teams around the world are hunting down the specific
genes involved.
One team, led by Joseph Piven of the University of North Carolina, has homed
in on WNT2, part of a family of genes which orchestrate brain development. WNT2
lies on chromosome 7, the region of our DNA most heavily linked with autism. At
least one person with autism has a break in the chromosome next to the WNT2
gene.
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Another reason the researchers chose WNT2 is because this gene is related to
dishevelled, a defective gene which makes mice behave in an autistic
way. 鈥淢ice with dishevelled show decreased grooming behaviour,
snuggling behaviour at night and mothering behaviour,鈥� says Thomas Wassink, a
key member of the team at the University of Iowa in Iowa City.
The investigators screened 135 patients with autism for mutations in the WNT2
gene, as well 160 healthy people. They drew a blank, except in two of the
autistic patients, who had a specific WNT2 mutation.
The link with autism was strong in those two families, because healthy
siblings didn鈥檛 have the mutations. Piven also discovered a second variation of
the WNT2 gene in 24 of the other autistic patients. 鈥淚t鈥檚 not conclusive by any
means, but it鈥檚 interesting and the data is good,鈥� says Wassink. The work will
appear in the American Journal of Medical Genetics.
The scientists admit problems explaining the absence of the key WNT2 mutation
in all but two autistic patients, however. 鈥淢ost people believe there are
anything from 3 to 15 genes involved in autism, so it鈥檚 not a one-gene disease,鈥�
says Wassink. But it gives us a valuable lead for further study, he says.
鈥淚t鈥檚 not going to explain what鈥檚 happening on chromosome 7 in autism,鈥� says
Anthony Monaco, whose team at the Wellcome Centre for Human Genetics in Oxford
is also hunting for autism genes. 鈥淏ut it will make a lot of us test this gene
to rule it in or rule it out.鈥�
Researchers are keen to find genes linked to autism because they should help
uncover the cause of the disorder, and perhaps lead to some kind of treatment.
Pinning down the genetic basis of autism would also make it possible to test IVF
embryos before implanting them.
But Monaco stresses that it will only ever be possible to tell prospective
parents how likely it is that their child will develop autism, not give a
definite yes or no. And Piven dismisses any suggestion that his work is a first
step towards testing embryos. 鈥淲e鈥檝e tapped into an abnormality which accounts
for a portion of what鈥檚 going wrong,鈥� he says. 鈥淏ut there are no clinical
implications at this point.鈥�