There was an article published some years ago about a sleep study (I think from Germany) that showed about 10-20% of people (European's I think) are genetically predisposed to function on a 30-hour* cycle. (As opposed to the 24 hour Circadian rhythm.)
*I think it was 30 hours, but don't know for sure. And I can't seem to find any reference to the study or what this "sleep disorder" is called. From Googling, I don't believe it is any of the following:
- Delayed sleep phase disorder
- Segmented Sleep Disorder
- Non-24-hour sleep-wake disorder
The study was most likely related to cognitive function and may have been funded by a space agency.
Hope this is on topic here, I just saw this site in Area 51 but didn't read much about it.