'Junk DNA' affects inherited cancer risk

Wednesday, 18 December, 2019

'Junk DNA' affects inherited cancer risk

A person’s risk of developing cancer is affected by genetic variations in regions of DNA that don’t code for proteins, previously dismissed as ‘junk DNA’, according to new research published in the British Journal of Cancer.

Led by an international team of scientists, the study sheds new light on why some people develop cancer while others don’t. It shows that inherited cancer risk is not only affected by mutations in key cancer genes — known as oncogenes and tumour suppressor genes — but that variations in the DNA that controls the expression of these genes can also drive the disease.

The researchers investigated 846 genetic changes within non-coding stretches of DNA, identified by previous studies as affecting cancer risk. These single-nucleotide polymorphisms (SNPs) are particular positions in the human genome where a single letter of the genetic code varies between people.

Unlike mutations in coding DNA such as BRCA, which are rare but significantly raise a person’s risk of developing cancer, non-coding SNPs are relatively common in the population but only slightly increase cancer risk. The team analysed whether there was a correlation between the presence of a particular SNP and the expression of particular genes, looking at over 6 million genetic variants across 13 different body tissues.

They found that variations in the regions that regulate the expression of oncogenes and tumour suppressor genes affect cancer risk. The study also revealed that these cancer-risk SNPs tend to be specifically located in regions that regulate the immune system and tissue-specific processes — highlighting the importance of these cellular processes to the development of cancer.

“What we found surprised us as it had never been reported before — our results show that small genetic variations work collectively to subtly shift the activity of genes that drive cancer,” said lead researcher Professor John Quackenbush, from the Harvard T.H. Chan School of Public Health. “We hope that this approach could one day save lives by helping to identify people at risk of cancer, as well as other complex diseases.”

“While minor genetic changes only have a small impact on cancer risk, the variations analysed in this study are numerous and common in the population,” added Dr Emily Farthing, Senior Research Information Manager at Cancer Research UK, who was not involved in the study. “This could begin to explain some of the variation in cancer incidence between individuals and families that cannot be explained through well-known cancer-risk genes or lifestyle factors alone.”

Understanding how non-coding DNA affects the development of cancer could thus improve genetic screening for disease risk, and may in future lead to new prevention strategies or help doctors diagnose the disease earlier.

The researchers’ next step will be to develop AI models to better predict cancer risk. They also aim to identify ‘control centres’ that regulate the expression of many genes relevant to cancer development, which could be targeted by new cancer treatments.

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