TORONTO—Night terrors, in which children exhibit sudden bouts of extreme fear and screaming an hour or two after going to sleep, appear to have a strong hereditary component, a new study suggests.
In a large study of twins, Canadian researchers have determined more than 40 percent of sleep terror cases likely can be attributed to genetics.

“The study brings strong evidence that genetics plays a major role,” said principal researcher Dr. Jacques Montplaisir, a professor of neuroscience and psychiatry at the University of Montreal.
“And in our other studies, we know that there’s a link between sleepwalking and night terrors.”
The study included 390 pairs of identical and fraternal twins, who were followed from birth and assessed for sleep terrors at 18 months and 30 months of age.
The researchers found that among identical twins, if one child had experienced the terrifying episodes during sleep, the chance that their twin would have the condition was about 68 percent at 30 months old.
For fraternal twins, the risk of both having night terrors was 24 percent.
“The sleep terrors are an abrupt and frightening sensation associated with sudden arousal and screams,” said Montplaisir, explaining the children’s heart rate and breathing speed up, they are sweaty and their faces flush, and they usually are inconsolable.
“And contrary to nightmares, the child doesn’t remember anything,” he said from Montreal.
“If you try to wake up a child during a night terror episode, the child is confused, he has no memory of any dreams, although on some occasions he may have just the impression of . . . a painful sensation without being able to give any description.
“Any attempt to waken the child may increase their agitation and prolong the episode,” he added. “Otherwise, most episodes will be brief and will cease abruptly and the child returns to deep sleep afterwards.”
Montplaisir said environmental factors also play a role in whether children are prone to sleep terrors.
Research has shown the incidents can be related to separation anxiety and exacerbated by tensions in the family, such as divorce or moving from one home to another.
Dr. Adam Moscovitch, medical director of the Canadian Sleep Institute, said it’s been known for some time that genetics plays a part in whether children suffer night terrors.
But Moscovitch noted other psychological and physiological factors also come into play—and he agreed separation anxiety is a common cause.
“It can very much be because, especially in that age group, waking up and not having the reassuring or assuring presence of a parent physically in the immediate proximity can trigger it,” he said from the Sleep Institute’s Toronto clinic.
“That’s where the whole concept [arose] of . . . getting attached to your little teddy bear or your blanky or sucking your thumb as a relaxing thing, as a replacement.”
Moscovitch, who also directs the institute’s other clinic in Calgary, said stress is one of the strongest behavioural underpinnings of sleep terrors. “The stress can be as simple as the impending arrival or actual arrival of another sibling.”
Although extremely frightening for parents, Montplaisir said sleep terrors are not linked to cognitive or behavioural problems in children and most grow out of the condition.
In his study, published today in the U.S. journal “Pediatrics,” the proportion of children experiencing sleep terrors had dropped to less than 20 percent at 30 months old from almost 37 percent at 18 months of age.