Epilepsy breakthrough for Adelaide researchers

By Melissa Trudinger
Monday, 11 March, 2002


A surprise finding by a team of Adelaide scientists has provided the first evidence that the same gene on the X-chromosome may be responsible for some forms of both epilepsy and intellectual disability.

The scientists, whose research is published today (March 11) on Nature Genetics online, discovered a gene that is linked with both conditions.

Principal investigator Dr Jozef Gecz, a senior scientist in the Cytogenetics Department at Adelaide's Women's and Children's Hospital, said that the finding was unexpected.

"This gene is found on the X-chromosome and is one of probably 100 genes on that chromosome, which when mutated, can cause intellectual disability," he said.

"The really novel aspect to this gene is its involvement in epilepsy as well as in intellectual disability."

The same mutation gave rise to very different clinical disorders, Gecz said.

"Our findings of mutations in this gene in the set of nine families with various clinical presentations - including West syndrome, Partington syndrome, myoclonic epilepsy, syndromic and non-specific intellectual disability - is quite unexpected," he said. The gene in question is different from other genes found to be involved in epilepsy. It is a homeodomain-containing gene, making it a master gene that controls other genes. In this case, the gene appears to be crucial to the development of the cortex.

"It will be very interesting to know the identity of these genes that are under control of this master gene, as they may potentially be involved in either epilepsy, intellectual disability, or both," said Gecz.

In addition, two of several mutations found was were polyalanine expansions, which can cause protein aggregation as seen in other polyalanine and polygluatamine disorders like Huntington's disease. Significantly, each family with this mutation had a different clinical presentation.

"We studied genetic material from nine families worldwide and found the same mutations in the gene gave rise to epilepsy, including infantile seizures (early childhood epilepsy) and other types of seizures, dystonia (disorder of muscle tone causing muscle contraction) as well as intellectual disability," Gecz said.

"We have no answers for why this occurs, but it is something we are keen to study further."

Gecz speculated that other genes and environmental influences were probably involved.

The nine families in the study came from Norway, Canada, Belgium and Australia, and included 50 affected individuals, all with varying degrees of mental retardation and about 60 per cent with various kinds of seizures. Up to two per cent of the population suffers from intellectual disability and another two per cent from epilepsy.

The implications of the discovery will be to assist with early diagnosis of non-specific intellectual disabilities in families and individuals, according to Gecz. However, he indicated that further experiments were needed before this would be possible.

"This is a very important piece of work," said Prof Grant Sutherland, head of the Cytogenetics Department.

"It's an interesting mutation as well as being highly clinically relevant. It will have a big impact on mental retardation and the development of diagnostics."

Sutherland said he believed the discovery would quickly lead to the development of a diagnostic for intellectual disabilities quite quickly.

Dr Gecz said that his group was primarily focussed on the study of intellectual disabilities, particularly those linked with mutations on the X-chromosome. He said that collaborations with epilepsy researchers, including those in his own department were now being considered.

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