circadian

"Early to bed and early to rise, makes a man stupid and blind in the eyes," quips a character in the science fiction story "Ender's Game." But scientists have now found a mother and daughter whose rare genetic mutation allows them to wake up refreshed on just six hours of sleep -- two hours less than the rest of the family requires.

The 69-year-old mother and 44-year-old daughter usually hit the sack around 10 p.m., and get up around 4 and 4:40 a.m., respectively. Both women have a genetic mutation which affects the regulation of circadian rhythms, or the body's natural clock.