Nightmares for children who are accompanied by a sudden crying during sleep, may be genetically determined.
Researchers from Montreal hospital have studied 390 pairs of identical twins aged between 1.5 years - 2.5 years.
In identical twins distortions in sleep are much more frequent than in those who aren't born a twin. Since the first genome are identical, this implies an hereditary nature, believe Canadian researchers, cited by BBC.
The results of previous studies show that sleep and sleep talking are also associated with genes.