Tiny pieces of RNA are turning out to play a big role in health. Over the past few years, scientists have found that these molecules, called microRNAs, are involved in key functions in cells and are linked to the development of certain cancers and other diseases. A new study led by scientists at Nanjing University, in China, finds that microRNAs circulating in blood can serve as a molecular "fingerprint" for cancers and diabetes. The findings raise the possibility that a simple blood test could help clinicians tailor treatments to individual patients.

MicroRNAs are tiny strands of RNA molecules that do not code for proteins as messenger RNAs do; instead, they bind to messenger RNA to help control the synthesis of proteins. Over the past few years, studies have found that microRNAs affect the way that genes are expressed in cells, and have linked specific microRNAs to particular cancers. Studies in recent months have shown that individual microRNAs associated with prostate cancer and lymphoma can be found circulating in the bloodstream. This would be a boon to oncologists, who currently rely primarily on expensive imaging and invasive biopsies.

In a new paper, published in Cell Research, scientists give the first comprehensive tally of microRNAs in blood serum and identify patterns of microRNAs that distinguish patients with two kinds of cancer and diabetes from healthy subjects. The researchers used sequencing technology to identify the type and levels of microRNAs in the blood serum of healthy people, and they found that these measurements are consistent from individual to individual. Next, they looked at the types of microRNAs and the levels in patients with lung cancer, colorectal cancer, and diabetes. For each condition, the researchers identified a unique pattern of microRNA expression that differed from that of healthy people.

Lead author Chen-Yu Zhang says that many scientists were surprised to discover that microRNA can be measured in blood serum, because the blood also contains ribonuclease, an enzyme that digests RNA. Although it's not yet clear how microRNAs escape destruction and persist in the blood, Zhang says, "whatever the reason, microRNAs are stable in the serum and are resistant to ribonuclease digestion."