"A range of sleep difficulties are associated with depression in school-aged children, and the overall association between the two difficulties maybe largely influenced by genes," report Dr. Alice M. Gregory of Kings College London, UK, and colleagues in the journal Pediatrics.

Sleep problems are thought to be related to anxiety and depression, but this relationship is complex and poorly understood. To help clarify the role of genetic and environmental factors in the anxiety-depression-sleep problem association, Gregory and her team studied 300 pairs of eight-year-old twins.

Twin studies are useful in teasing out genetic and environmental influences, the researchers note, because identical twins share the same genes and the same environment, while fraternal twins' genetic relatedness is the same as any other sibling pair, although their environment could be considered identical.

Parents reported any sleep problems the children had and the children were assessed for anxiety and depression.

While anxiety showed little relationship to sleep problems, children with sleep problems had higher levels of depression, the researchers found. The sleep problems included resistance at bedtime, delays in getting to sleep, anxiety associated with sleep, as well as sleep terrors and sleepwalking, related conditions called parasomnias.

Relationships between sleep and depression were stronger among identical twin pairs. According to the investigators, genes played the greatest role in this relationship, while the influence of environment was smaller.

"The large overlap between genes influencing depression and those influencing sleep problems suggest that it may be worth exploring whether genes that are known to influence depression are associated with sleep problems, and vice versa," Gregory and her team conclude. Genes related to the neurotransmitters serotonin or dopamine may be candidates, they add.

The findings also suggest that doctors should check for sleep problems in their young patients who show signs of depression, and vice versa, they add.

SOURCE: Pediatrics, September 2006.