Gene variant leads to six-fold increase in risk for certain brain tumours

A single-letter change in one gene may considerably increase a person's risk of developing particular forms of brain cancer, say researchers.

Dr Robert Jenkins, professor of laboratory medicine at the Mayo Clinic in Minnesota, USA, and co-author of the study said that the team was 'already starting to think about clinical tests that can tell patients with abnormal brain scans what kind of tumour they have, just by testing their blood'.

In the study, published in Nature Genetics, people with a G (guanine) nucleotide rather than an A (adenosine) nucleotide at one point in their genetic code were estimated to be almost six times more likely to develop certain glioma brain tumours.

Glioma tumours originate from specialised cells in the brain called glial cells and account for 20 percent of all brain tumours. The tumours linked to the gene variant are slower growing than most others but still lethal.

The letter change occurs in a part of the DNA that does not code for a protein. Professor Margaret  Wrensch, from the University of California, San Fransisco, who co-led the study, confirms: 'This is among the first examples that a change in a non-coding portion of DNA can be so strongly associated with cancer risk'.

A very labour intensive method of gene analysis, known as next generation sequencing, allowed the researchers to pick out the mutation while investigating single nucleotide polymorphisms on chromosome 8, an area already known to be implicated in brain tumour development.

Although the affected genetic region does not code for a protein, it is thought to code for a micro RNA, a type of small RNA molecule involved in the regulation of gene products that may affect the action of  particular cancer genes or even genome stability.

However, the exact genetic mechanisms are unclear. 'Understanding how this variant causes people to get these less aggressive, but still lethal, tumours will be extremely important', Professor Wresch commented. 'It may eventually lead to methods to reverse the course of these tumours or possibly to prevent their formation'.

Professor Jenkins added that 'one of the big challenges of the current genomic era is to assign functions to all these new gene variants'.