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THURSDAY, June 26 (HealthDay News) -- The lack of two related genes tied to autism may also disrupt the body's natural sleep cycle and cause further mental impairment, a new report says.

Mice lacking the fragile X mental retardation 1 gene (FMR1) and a similar gene called fragile X-related gene 2 (FXR2) have a very irregular, non-rhythmic sleep-wake pattern rather than the rodent's normal cycle of roughly under 12 hours awake and 12 hours asleep, according to a consortium of researchers led by scientists at Baylor College of Medicine in Houston.

"This has never been seen in a mouse before," lead researcher Dr. David Nelson, a professor of molecular and human genetics, said in a prepared statement.

The findings, published in the current issue of The American Journal of Human Genetics, are important, because children with autism or fragile X syndrome tend to have problems getting to sleep and staying asleep. Fragile X is the most common known cause of autism.

Nelson and a team of Dutch collaborators found the two genes do not perceive light, leading them to tests that concluded that the cell's "central clock" is normal, so the genes themselves must do something to alter the mice's natural rhythms.

"These genes [FMR1 and FXR2] are new players in the control of circadian [daily] rhythms," Nelson said.

More information

The Fragile X Research Foundation has more about fragile X syndrome.