Chronic fatigue syndrome or ME (CFS/ME) is surprisingly common in children with a prevalence of between 0.19% and 2% based on telephone surveys in the UK and the USA.1^–3 Lifetime prevalence (up to 30 years old) of self-reported CFS/ME, uncorroborated by a physician, of 0.8% has been reported from the 1970 British Birth Cohort.4 Lifetime prevalences (age 8–17) of disabling fatigue of 3 months’ and 6 months’ duration of 2.34% and 1.29% have been reported from a longitudinal cohort of twins.5 This means that almost all paediatricians reading this article will have seen and managed children with CFS/ME. Some paediatricians will have noted a family history of CFS/ME and may have wondered whether this was due to genetic heritability or an environmental factor. The causes of CFS/ME have long been debated, which has not necessarily been helpful to the clinical management of children with CFS/ME.6^–8 This article examines the evidence base for the genetic heritability of CFS/ME. This is an important area of knowledge for paediatricians as it will inform our discussions with children, young people and their families.

FAMILIAL AGGREGATION

The familial aggregation of CFS/ME was first described 16 years ago in Lyndonville, New York State. In this study, a questionnaire asking about symptoms of CFS/ME and possible risk factors (allergies, asthma, risk factors for infection and family history) was distributed to all 914 students at the Lyndonville Central School. Having a family member with CFS/ME was a strong predictor of CFS/ME, with a risk ratio of 35.99 (it is not clear from the study whether the authors only asked about first degree relatives or “any” relatives). The authors concluded that this …