Scientists have discovered a second short sleep gene, which is a gene that promotes natural short sleep, meaning 4-6 hours of sleep every night for an individual but they wake up feeling completely rested. The first gene was discovered in 2009 where researchers found that people who had a specific mutation in a gene called DEC2 got on average 6.25 hours of sleep every night but did not seem to have any negative effects from that short amount of sleep.
In the new study, researchers found another mutation in a gene called ADRB1 that was also linked with natural short sleep. It was found that humans with the mutated gene slept on average about 2 hours less than humans with the normal gene. Scientists performed experiments on mice with the mutated version of the gene. The mice with the mutated gene slept 55 minutes less than the normal mice. The ADRB1 gene was also shown at high levels in parts of the brain that are involved in subconscious activities. They also found that normal ADRB1 neurons were more active during wakefulness and REM sleep and they found that the mutated ADRB1 neurons were more active than the normal neurons, which likely was a factor of short sleep. I find it pretty interesting that genetics is the reason why some people can get 5 hours of sleep per night but still wake up completely refreshed the next morning. Perhaps by conducting more studies on short sleepers, they could help people who don't have the mutated gene to find ways to still feel refreshed in the morning even without as much sleep.