Genetic discovery may explain cancer risk mystery

Friday 14 February, 2014

Small risks that have been identified with common genetic variations could indicate the presence of much more influential rare mutations that are “hidden” according to international research which includes hundreds of Victorians.

The finding published in the PLOS Genetics journal today could help explain why research into the genetic causes of common diseases has failed to explain more than a fraction of the heritable risk of developing them.

The study shows for the first time in prostate cancer that small risks associated with some common genetic variants could actually be due to the presence of much more influential rare mutations that have yet to be found.

Led by scientists at The Institute of Cancer Research in London, the study also involved researchers from Cancer Council Victoria’s Cancer Epidemiology Centre (CEC) and many hundreds of Victorian research participants who contributed their DNA.

CEC Director Professor Graham Giles said the discovery could explain why the genetic mutations that have been discovered seem to have a small effect when studies of families have shown that genetic make-up has a large influence on our risk of cancer.

“Some have long suggested that DNA variations across the genome, which were found to have a weak association with diseases, are actually an artefact of another, hidden variant,” Professor Giles said, also an Honorary Professor at the University of Melbourne School of Population and Global Health.

“By collaborating on this very large study we were able to do ‘fine mapping’ work to measure a huge number of variants in the DNA for HOXB13, and we did in fact discover that a rare variant was more strongly associated with risk of prostate cancer. We believe this to be the first such example."

Prostate cancer is the most common cancer diagnosed in Victorian men with almost 4800 new cases recorded by the Victorian Cancer Registry in 2012 – accounting for 30 per cent of all cancers.

Whilst the majority of men will develop some form of prostate neoplasm during their lifetime, these are usually slow progressing and remain asymptomatic until their death with only a proportion of prostate tumours requiring clinical intervention.

Professor Giles said while the study did not indicate how widespread the phenomenon of rare variants may be, it does demonstrate the importance of digging deeper to identify the causal genetic changes behind common variants that have already been shown to be associated with risk of disease.

“If we can identify a small group of people who carry a rare genetic mutation, which is strongly associated with risk of certain cancers, then we may be able to use targeted screening to identify those at risk earlier.”