Tuesday February 8 2011
Sleepwalking sometimes runs in families
“Sleepwalking is in sufferers’ DNA,” reported The Daily Telegraph. It said research has found that people who sleepwalk have a faulty chromosome and that scientists believe this latest discovery raises hopes for a cure.
The news story is based on a genetics study that examined the DNA of 22 family members across four generations. Nine were sleepwalkers, and the family structure provided an opportunity to study whether and how sleepwalking may be inherited.
The results suggest a particular pattern of inheritance and point to variations in a region on chromosome 20. Importantly, these types of studies are not designed to identify actual genes that may be responsible. While these findings are important and are further evidence of a genetic component to sleepwalking, they must be considered as preliminary. A lot of work is still necessary to confirm these findings and identify the genes that may be responsible for sleepwalking. See the Live Well section for more advice on children's sleep.
Where did the story come from?
The study was carried out by researchers from Washington University School of Medicine. The research was partly funded by the Children’s Discovery Institute. It was published in the peer-reviewed medical journal Neurology.
The media reported this research clearly. They highlighted that the study found a particular section of DNA on chromosome 20 that appears to be inherited in sleepwalkers but has not yet identified the genes responsible.
What kind of research was this?
The researchers say that sleepwalking is known to run in families. Previous studies have suggested that sleepwalking has a genetic component, but the way the condition is inherited has yet to be established.
This study investigated the pattern of inheritance of sleepwalking by studying a family in which many of the members were sleepwalkers. This was a linkage study, which is a type of genetic study usually used to investigate the heritability of traits and to identify regions where responsible genes may lie by studying related individuals.
What did the research involve?
The study examined the DNA of a Caucasian family in which sleepwalking was common. The family spanned four generations. Of the 22 family members, nine were sleepwalkers while the remaining 13 were unaffected.
The family members were identified through a child who had been sleepwalking since the age of six and for whom medical treatment for sleepwalking had been sought. The other eight family members with the condition all started sleepwalking between the ages of 4 and 10, and had continued, albeit less frequently, into their 30s. Only two of the sleepwalkers were female, and seven were over 18 years of age.
The researchers obtained DNA from saliva samples from all family members and additional information was sought about sleepwalking or other troubles during sleep, such as sleep apnoea, night terrors, seizures and restless legs.
The researchers used methods common in this field to investigate patterns in the DNA of all the individuals, specifically looking at sections of DNA that appeared to be inherited in sleepwalkers.
What were the basic results?
Analysis of the DNA sequences from all the family members showed there were seven regions on chromosome 20 that were common in the sleepwalkers. According to the researchers, the region that appears to be linked to the condition is known to contain about 28 genes.
How did the researchers interpret the results?
The researchers say their results lend support to previous findings that sleepwalking has a genetic component. They say that other studies have suggested some models of heritability and their own study points to another way that the condition may be passed on. The particular pattern of inheritance identified by their study is called “autosomal with reduced penetrance”. “Autosomal” means that the gene is carried on the non-sex chromosomes and “reduced penetrance” means that the condition may appear to skip generations because not everyone who inherits the faulty genes has symptoms. It isn’t completely clear why only some people with the mutation develop symptoms, but this may be due to environmental, lifestyle and other genetic factors.
The researchers acknowledged that because other genetics studies have identified different models of inheritance, it is likely that sleepwalking can be inherited in different ways and is not linked to just one gene.
Linkage studies are important because they identify regions of the DNA that pass down through families, but they are not specific enough to identify genes. Sometimes, the region may contain many genes and further research is required to test whether the genes in the region are functional and what goes wrong with the function to cause disease.
While these findings are important and provide further evidence of a genetic component to sleepwalking, they have to be considered as preliminary. Much work is still necessary to identify the genes that may be responsible for sleepwalking.
It is also important to note that the family studied had severe sleepwalking that persisted into adulthood and the results from this study may not apply to the more common type that is limited to childhood.