While there is anecdotal evidence from ME/ CFS patients and carers that the illness can run in families – particularly mothers and their daughters or sons – is there any scientific evidence to back this up? Well, surprisingly there is. One survey of 914 students at the Lyndonville Central School in 1991 found symptoms of ME/CFS among other family members to be one of the strong predictors of ME/CFS in the student, with a high relative risk of 35.9 (other predictors included the ingestion of raw milk, and a history of allergy/ asthma). Again, one small family history study in 2001 found significantly higher rates of ME/CFS in the first-degree relatives of ME/ CFS cases compared with the relatives of control subjects. Finally, studies on twins have shown a higher “concordance” rate for ME/CFS between monozygotic (identical) twins than between dizygotic (nonidentical) twins – suggesting that genetic factors might have an important role.
Building upon these reports, researchers at the University of Utah focused on ME/ CFS using specialist methods previously used to investigate heritable components of diseases such as prostate cancer, influenza mortality, aneurysm, cancer, and diabetes. From genealogical records of Utah pioneers and their descendants, representing 15 generations of genealogy data, cross referenced against medical diagnosis data from 1993, a sample group of 811 was chosen. The Genealogical Index of Familiality (GIF) statistic was used to test the hypothesis of “excess relatedness” among ME/CFS cases.
The results showed that the “average relatedness” of ME/CFS cases was significantly greater than expected when all relationships were considered (p<0.001) – strong evidence for excess clustering of the illness in families. This could be due to either a shared environmental factor (location, diet, infection) or shared genes, or a combination of the two. However, there was also a significant “relative risk” of ME/CFS amongst first, second and third degree relatives of existing ME/CFS patients compared with “control” individuals.
As the Table shows, first-degree relatives (parent/offspring) had nearly three-times the risk (relative risk of 2.70) of also having ME/CFS, while seconddegree relatives (siblings or grandparent/ grandchild) had 2.3 times the risk. The authors point out that this strongly supports a genetic contribution to a predisposition to ME/CFS as it has been defined and diagnosed by clinicians in Utah since 1993, and that their study is the first population-based analysis to present such evidence.
Reference: Evidence for a heritable predisposition to Chronic Fatigue Syndrome. Albright F et al. BMC Neurol 2011 May 27; 11: 62.