E2 ModerateModerate confidencePEM not requiredCross-SectionalPeer-reviewedReviewed
Standard · 3 min
Twin analyses of fatigue.
Schur, Ellen, Afari, Niloofar, Goldberg, Jack et al. · Twin research and human genetics : the official journal of the International Society for Twin Studies · 2007 · DOI
Quick Summary
This study looked at whether fatigue and ME/CFS run in families by studying twins. Researchers asked over 1,000 pairs of identical twins and 800 pairs of fraternal twins about their fatigue symptoms. They found that in men, genetics played a bigger role in fatigue, while in women, life circumstances and personal experiences were more important.
Why It Matters
Understanding whether fatigue and ME/CFS have genetic components could help identify who is at risk and guide future research into biological mechanisms. The finding that genetic and environmental contributions differ by sex suggests that treatment approaches or prevention strategies may need to be tailored differently for men and women.
Observed Findings
In males, monozygotic twin pairs showed higher correlations for prolonged and chronic fatigue than dizygotic pairs, suggesting genetic influence.
Approximately 50% of variance in prolonged and chronic fatigue in males was attributed to genetic effects.
In females, individual-specific environmental effects accounted for most variance in prolonged and chronic fatigue.
For CFS specifically, genetic influences appeared more relevant in women than the broader fatigue phenotypes.
Correlation patterns differed substantially between sexes, indicating sex-dependent genetic or environmental factors.
Inferred Conclusions
Genetic factors contribute substantially to fatigue phenotypes in males but play a smaller role in females.
Individual-specific (non-shared) environmental factors are important contributors to fatigue in both sexes, particularly in women.
The etiologic architecture of fatigue and CFS may be sex-dependent, with different proportional contributions of nature versus nurture.
Future investigations should account for sex differences when studying fatigue etiology.
Remaining Questions
What specific genetic variants contribute to fatigue susceptibility, particularly in males?
What This Study Does Not Prove
This study does not prove what specific genes cause fatigue or ME/CFS, nor does it identify which environmental factors are responsible. Twin studies can show that genetics matter, but they cannot pinpoint causal mechanisms or determine whether associations reflect true biological inheritance versus shared family environments and behaviors.
Tags
Symptom:Fatigue
Method Flag:PEM Not DefinedWeak Case DefinitionSex-Stratified
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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