Researchers at the American Academy of Sleep Medicine conducted a study to find out why a small percentage of people appear to only need six hours of sleep whereas most everyone else needs between eight and nine hours for optimal functioning during the day.

They worked with 100 pairs of twins and identified a gene mutation that allows one not only to function on less sleep but also to experience fewer effects of sleep deprivation even after an all-nighter.

The gene in question is called BHLHE41 and the variant is called p.Tyr362His for identification purposes, and individuals with the variant slept just five hours per night on average.

On the flipside, the twin without the mutation slept an hour and five minutes longer and struggled more in attempting to perform after 36 sleepless hours than his sibling with the variant.

Cognitive performance was measured every two hours during the sleep deprivation period by means of the Psychomotor Vigilance Test.

After this period of extended sleep deprivation, the twin without the variant slept for 9.5 hours while his brother or sister slept just eight hours to catch up.

"This work provides an important second gene variant associated with sleep deprivation and for the first time shows the role of BHLHE41 in resistance to sleep deprivation in humans," says lead author Renata Pellegrino, PhD, senior research associate in the Center for Applied Genomics at The Children's Hospital of Philadelphia. "The mutation was associated with resistance to the neurobehavioral effects of sleep deprivation."

All sets of twins were the same sex, and 59 pairs were identical while 41 were dizygotic, meaning they were from separate zygotes, also known as sperm and egg cells, from each parent. Identical twins occur when an egg cell divides in two after fertilization.

Study participants were healthy, and their sleep was measured by means of actigraphy over the course of eight nights.

"This study emphasizes that our need for sleep is a biological requirement, not a personal preference," says American Academy of Sleep Medicine President Dr. Timothy Morgenthaler. "Most adults appear to need at least seven hours of quality sleep each night for optimal health, productivity and daytime alertness."

The AASM remarks that six hours of sleep or less is simply not enough for those without the gene mutation and that those who attempt to thrive on so little sleep without the variant risk health consequences.

The study was published in the journal SLEEP.