New gene discovery linked to ‘Rain Man’ brain condition

Associate Professors Paul Lockhart and Rick Leventer led an international team who have discovered the first gene (DCC) known to cause the loss of the main connection between the two halves of the brain, in the absence of any other syndromes linked to the condition.

About one in 4000 babies are born with this condition, called agenesis of the corpus callosum (ACC). The corpus callosum (CC) is a bundle of about 200 million nerve fibres and is crucial for communication between the brain's hemispheres.

Symptoms of ACC, where the corpus callosum is missing, are varied but can include intellectual disability, autism and cerebral palsy. Individuals with ACC who also have the DCC gene change often struggle with 'mirror movements'. This means if they move one hand, the other hand automatically moves in the same way. This causes problems with everyday tasks including eating, washing the dishes, writing, driving cars and using a mobile phone or tablet.

Megasavant Laurence Kim Peek, who inspired the Rain Man character Raymond Babbitt, was born without a corpus callosum. Scientists speculated Peek's increased memory capacity was because his neurons made unusual connections due to the absence of these nerve fibre tracts. Peek did not have autism as commonly thought but a rare genetic condition, FG Syndrome.

A/Prof Lockhart and A/Prof Leventer identified a gene called DCC (Deleted in Colorectal Cancer). Their study suggests individuals with ACC caused by mutations in this gene have much better neurodevelopmental outcomes than people with ACC linked to a particular syndrome.

This holds important implications for decision-making if the condition is detected during prenatal testing.
"The results of this research will provide better information to parents regarding potential outcomes for their children, helping to make more informed reproductive decisions," neurogenetics researcher A/Prof Lockhart said.

"Our research also provides important new information about how nerves connect to the appropriate part of the brain during development of the embryo," he added. "This has potential implications for our understanding of a broad range of neurodevelopmental conditions such as autism spectrum disorder.

"This gene is playing a role in how nerves connect with each other and transfer information. Deficits or problems in this process are emerging as associated with autism spectrum disorder," A/Prof Lockhart said.

The finding was published in the prestigious scientific journal Nature Genetics.

Neuroscience researcher A/Prof Leventer said ACC is one of the best known but least understood abnormalities of human brain development.

"The outcomes are very variable, from patients with normal intellect to patients with severe disabilities and the entire spectrum in between," he said.

"One of the tangible benefits of our discovery is that we might be able to reassure parents whose child has ACC due to a mutation in the DCC gene, that these children are usually unaffected or only mildly affected, as our study shows."

Together with colleagues in Europe and North America, the researchers used genetic sequencing and sophisticated brain imaging technology known as diffusion MRI tractography to study multiple individuals from four different families and 70 unrelated individuals with ACC.