Staying up late linked to genetic mutation

170407 night owl full
A real, not figurative, night owl. Specifically a Great Horned Owl (Bubo virginianus).
Credit: Greg Hume

Find it difficult to fall asleep at night, and then end up sleeping in or waking up tired, feeling like zombie for the rest of the day? The cause of sleep disorders can be complex, a combination of environmental, physiological and psychological factors, but you may have inherited a genetic anomaly that causes your biological clock to run perennially out of whack with the rest of the planet.

Genetics researchers in the United States and Turkey have identified a mutation in one of the core genes regulating the human body’s circadian rhythms that prolongs the wake cycle, delaying the onset of sleep. Those carrying the genetic mutation were typically found to sleep more than two hours later than those without it, according to the research, published in the journal Cell

“Carriers of the mutation have longer days than the planet gives them, so they are essentially playing catch-up for their entire lives,” says first author Alina Patke, of the Laboratory of Genetics at The Rockefeller University in New York.

The research began with studying skin cells of subjects diagnosed with delayed sleep phase disorder (DSPD), a persistent inability to fall asleep at conventional and socially required times. The disorder is associated with an inability to conform to socially expected schedules, meaning poor academic or work performance, physiological impairment including cardiovascular disease and diabetes, and psychological conditions including anxiety and depression.

The study led to the identification in many people with DSPD of a mutation in one of the key genes that drive the body’s circadian clock.  

The mutation found by the researchers was a single-point error (with just one incorrect letter in the genetic instructions) in the Cry1 gene, which produces the CRY1 “cryptochrome” protein (which is responsive to blue light).

The CRY1 protein regulates circadian clocks in both plants and animals. In humans and other mammals, it functions independently of light, as a cellular-level “peripheral clock” working together with the “central clock” within the suprachiasmatic nucleus (SCN) of the brain, which is driven primarily by light signals direct from the retina. 

Attuned to the wake cycle through neuronal and hormonal signals from the SCN, the CRY1 protein acts as a clock “repressor”, producing cell activators but also inhibitors that gradually silence the function of the activators over time. In those carrying the Cry1 gene mutation, the CRY1 protein they produce is incomplete, causing the silencing process to take longer, thus leading to a delayed onset of sleepiness. 

The researchers suggest the mutation is likely to be carried by 1 out of 75 people, with greater frequency in some families due to its inheritability.

But even having the genetic mutation is not necessarily something to lose sleep over. The gene is just one part of the body’s clock complex, so extra attention to the factors driving the other components, such as exposure to bright light in the morning, exercise, and limiting light stimulation at night, should make it possible to overcome the negative effects of the mutation.

“An external cycle and good sleep hygiene can help force a slow-running clock to accommodate a 24-hour day,” Patke says. “We just have to work harder at it.”

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