Dr. Tom A. Fowler of Cardiff University in Wales, the study's lead author, tells Reuters Health that unexplained disabling fatigue "can't be thought of as just depression in another form."
Given that depression often accompanies fatigue and vice versa, Fowler and his team performed a twin study to investigate environmental and genetic influences on both conditions.
The researchers looked at 2,398 pairs of twins between the ages of 8 and 17. Fatigue was considered disabling if it interfered with at least one aspect of school, leisure activities or relationships with family or peers, and if it required the child to rest for at least an hour daily. Fatigue was classified as short term if it lasted longer than one week, and long-term if it lasted more than a month.
Both short- and long-term fatigue appeared to have genetic roots, the researchers found, while the environmental influence for short-term fatigue was stronger than the familial influence.
The analysis found that while fatigue frequently accompanied depression, it showed a different pattern of genetic and environmental influences, with the researchers concluding that, "This suggests that fatigued states in children should be considered as valid entities in their own right and not as variants of depression." Individuals with fatigue may become depressed in response to this "disabling disorder."
The cause of chronic fatigue in children, which may be related to chronic fatigue syndrome (CFS) in adults, remains unclear, Fowler notes.
