A new study of twins suggests that insomnia in childhood and adolescence is partially explained by genetic factors.
Results show that clinically significant insomnia was moderately
heritable at all stages of the longitudinal study. Genetic factors
contributed to 33 to 38 percent of the insomnia ratings at the first two
stages of the study, when participants had an average age of 8 to 10
years. The heritability of insomnia was 14 to 24 percent at the third
and fourth follow-up points, when the average age of participants was 14
to 15 years. The remaining source of variance in the insomnia ratings
was the non-shared environment, with no influence of shared, family-wide
factors. Further analysis found that genetic influences around age 8
contributed to insomnia at all subsequent stages of development, and
that new genetic influences came into play around the age of 10 years.
"Insomnia in youth is moderately related to genetic factors, but the
specific genetic factors may change with age," said study author Philip
Gehrman, PhD, assistant professor in the Department of Psychology at the
University of Pennsylvania in Philadelphia. "We were most surprised by
the fact that the genetic factors were not stable over time, so the
influence of genes depends on the developmental stage of the child."
Study results are published in the January issue of the journal Sleep.
Insomnia involves difficulty initiating or maintaining sleep, or
waking up earlier than desired, according to the American Academy of
Sleep Medicine. Children with insomnia may resist going to bed on an
appropriate schedule or have difficulty sleeping without intervention by
a parent or caregiver. An insomnia disorder results in daytime symptoms
such as fatigue, irritability or behavioral problems.
According to the authors, the results suggest that genes controlling
the sleep-wake system play a role in childhood insomnia. Therefore,
molecular genetic studies are needed to identify this genetic mechanism,
which could facilitate the development of targeted treatments.
"These results are important because the causes of insomnia may be
different in teens and children, so they may need different treatment
approaches," said Gehrman.
The study group comprised 1,412 twin pairs who were between the ages
of 8 and 18 years: 739 monozygotic pairs, 672 dizygotic pairs and one
pair with unknown zygosity. Participants were followed up at three
additional time points. Average ages at each of the four waves of the
study were 8, 10, 14 and 15 years. Results were interpreted in terms of
the progression across time, rather than differences between discrete
age groups. Clinical ratings of insomnia symptoms were assessed by
trained clinicians using the Child and Adolescent Psychiatric Assessment
and rated according to the Diagnostic and Statistical Manual of Mental
Disorders, 3rd Edition.
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