Some people live for the night. Their anomalous circadian clocks, which allow them to party until dawn and sleep when the sun shines, have puzzled biologists for ages. Scientists know they have a condition called “delayed sleep phase disorder,” but the true origin of their night owl tendencies has only now become clear.

In the journal Cell, researchers from the Rockefeller University recently reported that people who tend to stay up all night share one thing in common — mutations in a single gene, CRY1, which in its normal form encodes a key protein that keeps the body’s circadian clock running smoothly. Their analysis began by looking at the genes of a single person with delayed sleep phase disorder, which they define as a condition where “sleep episodes are shifted to later times misaligned with the societal norm.”

Turns out that the first individual they studied was related to five others who had trouble sleeping and had the same genetic mutation. To rule out the possibility that the genetic variation was just a familial quirk, they turned their attention to six families in Turkey, the members of whom also had sleep issues. They, too, carried mutated versions of that gene, which was linked to irregular sleep patterns and a delay in normal sleeping schedules of 2 to 4 hours.

Ultimately, this mutation throws a wrench in the inner clockwork of the the body’s circadian clock, which is genetically encoded. The gene CRY1 contains the instructions for producing a protein of the same name, which, according to the researchers, is a “critical” regulator of the body’s circadian rhythms. The mutation in the CRY1 gene seems to make a super-regulator: “Expression of this more potent CRY1 form (CRY1 D11) is associated with a lengthened period of molecular circadian rhythms in cells,” they write, explaining that it’s ultimately this super-regulator that lengthens circadian cycles so far past their normal bounds.

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Of course, the discovery of this gene isn’t the final word on the biology of night owls — like a clock whose many gears must work in concert, there are many ways in which the genes that work together to regulate circadian rhythms can go wrong. On Wednesday, a separate study in Scientific Advances reported that another mutated gene, FABP7, was linked to interrupted sleep and shorter periods of sleep in general — not just in humans but in mice and fruit flies, as well. Other studies have found genes associated with being extra-tired all the time, and still others have shown that some people bounce back from a sleepless night better than others.

Taken together, these discoveries about the circadian clock confirm one thing: This thing is pretty damn complicated. Teasing out the genetic basis of sleep disorders, however, will hopefully lead to drug-based interventions for people who no longer want to be night owls. In the meantime, sufferers can try to override their internal clocks by sticking to a strict sleep schedule — or they can simply learn to embrace their inner timekeeper.