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'.