Biomarker for Human Sleepiness Identified

Deprived of sleep one tends
to fall asleep everywhere

Researchers hope to make amylase the first of a panel of biomarkers that will aid diagnosis and treatment of sleep disorders and may one day help assess the risk of falling asleep at the wheel of a car or in other dangerous contexts.

Paul J. Shaw´s, Ph.D., assistant professor of neurobiology lab was the first to show that fruit flies enter a state of inactivity comparable to sleep. To identify a marker for sleep debt, Shaw decided to look in saliva. To start his search, Shaw subjected the flies to different kinds of sleep deprivation and used microarrays to look for changes in activity in many different genes. Amylase levels consistently changed after sleep loss. Amylases are a family of enzymes found in the saliva that break down starch.

To verify amylase's connection to sleep loss, Shaw's lab monitored its activity level after sleep deprivation in different fruit fly lines genetically altered to modify their sleep drive. In one key test, amylase did not increase in a fly modified to endure sleep deprivation longer than normal flies without incurring sleep debt. When scientists kept the same mutant flies awake for extended nine or 12 hour stretches that normally cause them to incur sleep debt, their amylase levels increased.

"This helped prove that the increases in amylase activity level we were seeing weren't just triggered by wakefulness," Shaw says. Humans kept awake for 28 hours also had increased amylase levels versus controls allowed to sleep normally.

"We're very pleased with how tightly amylase levels correlate with sleep debt, but for a good diagnostic test we're likely going to need more than one biomarker," Shaw says. "So we're going to continue to use the processes that we've developed to look for other substances that change in connection with the level of sleep debt."; Source: Washington University School of Medicine