Saliva test may catch deadly diseases early

A simple saliva test may be capable of diagnosing diabetes and cancer, and even neurological disorders and autoimmune diseases at an early stage, scientists say.
The study, the most comprehensive analysis ever conducted of RNA molecules in human saliva, found that saliva contains many of the same disease-revealing molecules that are contained in blood.
"If we can define the boundaries of molecular targets in saliva, then we can ask what the constituents in saliva are that can mark someone who has pre-diabetes or the early stages of oral cancer or pancreatic cancer - and we can utilise this knowledge for personalised medicine," said Dr David Wong, a senior author of the research and University of California, Los Angeles's Felix and Mildred Yip Endowed Professor in Dentistry.

Wong said the test also holds promise for diagnosing Type 2 diabetes, gastric cancer and other diseases.
For the research, Wong collaborated with Xinshu Xiao, the paper's other senior author and a UCLA associate professor of integrative biology and physiology.
Using state-of-the-science genomics and bioinformatics, the researchers analysed 165 million genetic sequences.

Among the many forms of RNA are some unusual ones that live in the mouth and in cells. For example, it wasn't known until very recently that RNA comes in a circular form; the linear form has long been known.
But the UCLA scientists identified more than 400 circular RNAs in human saliva - the first discovery of circular RNA in saliva or any body fluid - including 327 forms that were previously unknown.

Circular RNA's function in saliva is not entirely understood, although it does serve as a sponge for tiny RNA molecules called microRNAs, which bind to it.
It's likely that circular RNAs in saliva protect microRNAs from being degraded, Xiao said.
The scientists compared microRNA levels in saliva to those in the blood and other body fluids, and found the levels of microRNA in blood and in saliva are very similar - indicating that a saliva sample would be a good measure of microRNAs in the body.
They also found that saliva contains another class of small RNAs, called piwi-interacting RNAs, or piRNAs, which are produced by stem cells, skin cells and germ cells.

There are very few piRNAs in blood and most other body fluids, but Xiao's analysis showed that piRNA are abundant in saliva. Although their function is not yet known, Xiao said they may protect the body from viral infection.
"Saliva carries with it non-coding RNAs, microRNAs, piRNAs and circRNAs that are biomarkers for disease and health monitoring," said Wong.
"Had we not done this collaboration, we would never know that non-coding RNAs, microRNAs, piRNAs and circRNAs exist in saliva," Wong said.