Twin study shows there is a genetic component to insomnia

According to a study on twins, there is a genetic component to insomnia.

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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Can Low Birth Weight Raise Autism Risk?

After studying data on more than 3,700 pairs of identical twins, researchers from Northwestern University found that low birth weight was associated with more than triple the risk for autism spectrum disorder among twins in which autism only affected one of the children.

"That only one twin is affected by ASD [autism spectrum disorder] in some identical twin pairs suggests that environmental factors may play a role either independently or in interaction with autism risk genes," study author Molly Losh, director of Northwestern's Neurodevelopmental Disabilities Laboratory, said in a university news release.

"Our study of discordant twins -- twin pairs in which only one twin was affected by ASD -- found birth weight to be a very strong predictor of autism spectrum disorder," she added.

The study, which was released online in advance of publication in an upcoming print issue of the journal Psychological Medicine, used data from the Swedish Twin Registry's Child and Adolescent Twin Study.

In analyzing twins in which one baby was more than 14 ounces, or at least 15 percent heavier at birth than the other, the researchers found the risk for autism rose 13 percent for every 3.5 ounce drop in birth weight.

The study results suggested that birth weight could play a role in the complex causes of autism by interacting with a child's underlying genetic predisposition, or likelihood, of developing the condition, the researchers said.

Losh added that because autism is a developmental disorder involving early brain development, prenatal and perinatal environmental factors, such as birth weight, may be especially important.

The researchers noted, however, their findings may not apply to children who are not part of a multiple-birth pregnancy.

While the study found an association between birth weight and autism risk, it did not prove a cause-and-effect relationship.

Read more: http://www.nlm.nih.gov/medlineplus/news/fullstory_121145.html

Another Clue in the Mystery of Autism

Although the genetic basis of autism is now well established, a growing body of research also suggests that environmental factors may play a role in this serious developmental disorder affecting nearly one in 100 children. Using a unique study design, a new study suggests that low birth weight is an important environmental factor contributing to the risk of autism spectrum disorder (ASD).

"Our study of discordant twins -- twin pairs in which only one twin was affected by ASD -- found birth weight to be a very strong predictor of autism spectrum disorder," said Northwestern University researcher Molly Losh. Losh, who teaches and conducts research in Northwestern's School of Communication, is lead author of the study that will be published in the journalPsychological Medicine and is now available online.

Prior twin studies have shown that when one identical twin had ASD, the other twin was much more likely to have ASD than not. "Because identical twins share virtually 100 percent of their genes, this is strong evidence for the role of genetics in autism," said Losh. "Yet it is not 100 percent the case that ASD affects both identical twins in a twin pair."

"That only one twin is affected by ASD in some identical twin pairs suggests that environmental factors may play a role either independently or in interaction with autism risk genes," she added. "And because autism is a developmental disorder impacting brain development early on, it suggests that prenatal and perinatal environmental factors may be of particular importance."

The researchers found that lower birth weight more than tripled the risk for autism spectrum disorder in identical twin pairs in which one twin had ASD and the other did not.

To control for shared genetic and environmental factors, the researchers used a co-twin control study design in which the ASD-affected twin served as the case and the unaffected twin served as the control. They found the risk for autism spectrum disorder rose 13 percent for every 100 gram- (3.5 ounce-) decrease in birth weight.

"There's been a great deal of misinformation about the causes of autism -- from the 1950s misconception that the distant maternal behavior of what were dubbed "refrigerator mothers" was at fault to the ill-informed myth that vaccines can cause autism," said Losh.

Losh and her colleagues' findings add to a growing body of knowledge about the complex causes of autism and suggest that birth weight could be one of the environmental features that interacts with underlying genetic predisposition to autism.

Losh, who directs Northwestern's Neurodevelopmental Disabilities Laboratory, warned that the findings from twin studies might not extend to singletons, as the prenatal and perinatal conditions for twins and singletons differ in important ways.

The researchers studied a population-based sample of 3,725 same-sex twin pairs that were part of the Swedish Twin Registry's Child and Adolescent Twin Study that was directed by Paul Lichtenstein of Sweden's Karolinska Institute. The discordant twins they studied were pairs in which one twin was more than 400 grams (about 14 ounces) or at least 15 percent heavier at birth than the other.

Read more: http://www.sciencedaily.com/releases/2012/01/120119143334