A new study provides strong support for the notion that the tendency to sleepwalk is hereditary, passed from parent to child through some as-yet-unidentified gene.
Compared to children with no family history of sleepwalking, children with one parent who had ever been a sleepwalker were three times more likely to sleepwalk themselves, researchers found. If both parents had a history of sleepwalking, the odds that their child would be a sleepwalker as well rose by a factor of seven.
"These findings point to a strong genetic influence on sleepwalking," the study authors wrote Monday in the journal JAMA Pediatrics.
Sleepwalking, or somnambulism, doesn't always involve walking. A person is said to be sleepwalking if they are performing a complex task -- talking, sitting up in bed, getting dressed -- while in a state of deep sleep, according to the National Sleep Foundation. It is more common in children than adults, though some people never outgrow it.
For the new study, researchers examined data on nearly 2,000 children who were born in the Canadian province of Quebec in 1997 or 1998 and tracked until 2011. Starting when the children were 2.5 years old and continuing until they turned 13, researchers asked their mothers whether their children had sleepwalked in the last year. If so, they were asked whether the frequency of sleepwalking was best described as "sometimes," "often" or "always."
In addition, when the children were 10, the mothers were asked whether they or their child's father had ever been a sleepwalker.
The researchers found that the prevalence of sleepwalking in children peaked around the age of 10, when 13.4% of children engaged in these nighttime excursions. That figure held pretty steady as children approached their teen years, with 12.8% of 13-year-olds reporting sleepwalking incidents in the last year.
Altogether, 29% of children in the study said they had sleepwalked at some point in their childhood, according to the study.
When grouped according to family history, the researchers found that 22.5% of children with no family history of sleepwalking became sleepwalkers on at least one occasion. That prevalence more than doubled -- to 47.4% -- among children who had at least one parent with a sleepwalking past and nearly tripled -- to 61.5% -- for children who counted both parents as sleepwalking veterans.
The researchers also found that youths who had suffered night terrors as young children were nearly twice as likely to become sleepwalkers after the age of 5. Unlike nightmares, which cause children to wake up abruptly, children in the midst of a night terror can spend up to 30 minutes crying, screaming and often sweating while they are only partially awake.
It's possible that sleepwalking and night terrors are actually two different manifestations of a single physiological condition, the study authors wrote. Both conditions occur during the sleep stage known as slow-wave sleep, when people sleep deeply and the brain consolidates new memories.
Scientists don't know which gene variants are responsible for sleepwalking, but the study results suggest they could have something to do with regulating slow-wave sleep, the authors wrote.
Even without knowing which particular piece of DNA is passed down from parent to child, simply realizing that sleepwalking has a strong hereditary component can be useful for parents.
"Parents who have been sleepwalkers in the past, particularly in cases where both parents have been sleepwalkers, can expect their children to sleepwalk and thus should prepare accordingly," the study authors wrote.
That means making an effort to shield their children from things that are known to trigger sleepwalking, such as irregular sleep schedules, sleep deprivation and "noisy sleep environments." In extreme cases, parents might even want to invest in a home alarm system to make sure sleepwalking children don't venture outside while asleep.