While chronic fatigue and depression commonly co-occur in children, the two conditions have largely distinct etiologies, UK study findings show.

Chronic fatigue and depression have distinct etiologies

While chronic fatigue and depression commonly co-occur in children, the two conditions have largely distinct etiologies, UK study findings show.

"This suggests that fatigue states in children should be considered as valid entities in their own right and not as variants of depression," note Tom Fowler, from Cardiff University in Wales, and colleagues.

To examine the degree of overlap in genetic and environmental influences between symptoms of depression and fatigue, the team asked the parents of twins aged between 8 and 17 years to complete a questionnaire regarding the presence of disabling fatigue in both twins. Twins aged 11 years or older also completed the Mood and Feelings Questionnaire (MFQ).

Patient-rated data were obtained for 1468 twin pairs and self-rated information from older twins was available for 930 twin pairs.

In all, 129 individuals were categorized as suffering from short-duration fatigue and 73 individuals from prolonged fatigue. The average self-rated scores on the MFQ were 11.26 for monozygotic twins and 11.90 for dizygotic twins.

Genetic analysis showed that both short-duration and chronic fatigue in children are largely familial, with shared environment playing a more important role in prolonged than acute fatigue.

Disabling fatigue did share some etiological influences with depression, but only 22% of the variance in disabling fatigue was explained by factors common to both conditions. Shared environment accounted for 13% and genetic factors for only 8%.

The researchers suggest in the British Journal of Psychiatry that the increase in the importance of shared environment may be due to the impact of viral illness and shared life events, which are risk factors for both depression and fatigue.

For both short-duration and prolonged fatigue, the majority of the genetic and environmental variance was specific to disabling fatigue and distinct from depression, although the phenotypic correlation between prolonged fatigue and depression was slightly higher than that between short-duration fatigue and depression.

Fowler and co-workers summarize: "Disabling fatigue and depression co-occur but appear to have distinct genetic and environmental etiologies."


British Journal of Psychiatry 2006; 189: 247-253