The brain lacks the fibres that connect the left and right hemispheres.

Rain Man gene identified

Gettyimages 530326346
For people with agenesis of the corpus callous, the brain lacks the fibres that connect the left and right hemispheres.
Credit: Shubangi Caneshrao Kene

 

A gene responsible for mild cases of the brain
disorder behind the 1988 hit movie Rain
Man
has been identified.
 

Kim Peek was the real-life ‘mega-savant’
who inspired the Oscar-winning movie. But aside from his phenomenal ability to
memorise books word-for-word, Peek’s brain was odd.

One striking feature was that it  lacked the thick
bundle of nerve fibres – the corpus callosum – that usually bridges the divide
between the left and right hemispheres.   

The condition, called agenesis of the
corpus callosum, or ACC, isn’t that uncommon. It affects around one in 4000 newborns,
and an estimated 3-5% of children with an intellectual disability. It is also a
common cause of terminations in the later stages of pregnancy.

But it’s a baffling condition. It can crop
up along with a constellation of other brain malformations – as it did in
Peek’s case – or on its own. And the effects can vary dramatically, making it
difficult for clinicians to give anxious parents or pregnant couples a clear idea
of what to expect.

“The outcomes are very variable, from
patients with normal intellect to patients with severe disabilities and the
entire spectrum in between,” says Rick Leventer from the Murdoch Children’s
Research Institute in Melbourne, who led the study.

But findings by Leventer and an
international team of collaborators means that clinicians can now put some
parents’ minds at ease.

Their work, published by Nature Genetics, has uncovered a gene
responsible for mild cases of ACC.

Based on previous studies, the team homed
in on a gene called DCC. Knock the
gene out in mice, and the corpus callosum fails to form. The team surmised that
DCC mutations might do the same in
people.

Previous work has only linked the DCC gene to another condition – mirror
movements disorder (MM) – a frustrating condition where people can’t stop one
side of their body from mirroring what the other side is doing.

The team investigated four multigenerational
families with one or more cases of ACC or MM, as well as 70 unrelated
individuals with ACC.

Mutations in the DCC gene were responsible for all cases of ACC and MM in the
families studied, and in five of the unrelated cases.

Importantly, all of these ACC cases were
mild – the people studied had either normal or borderline impaired intellectual
capacity, but not severe intellectual disability. 

The finding will help in assessing cases
of ACC in newborns or unborn babies. If the test shows that a DCC mutation is the culprit, parents can
be reassured that the consequences of the condition are likely to be mild.