Researchers have followed up on previous research that identified a gene linked to Delayed Sleep Phase Disorder (DSPD) in one person, reports Live Science.

In the new study, Patke’s team confirmed CRY1 genetic mutation’s link to delayed sleep phase disorder by looking for the mutation among the woman’s extended family, and in other population samples.

Using a database of genomic information for people in Turkey, the researchers identified people who carried the mutation in CRY1. In collaboration with researchers at Bilkent University in Ankara, Turkey, the researchers reached out to these people, and were able to conduct interviews and perform further DNA sequencing with the members of six families.

Among the Turkish family members, 39 carried the CRY1 mutation, and 31 did not. Data revealed that the sleep cycles of those carrying the gene were clearly late-shifted. Their midpoint of sleep naturally fell between 6 a.m. and 8 a.m., while the midpoint of sleep for those who did not carry the mutation fell around 4 a.m.

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