By Suzanne Vernon, PhD, Scientific Director
A biomarker is an indicator of a biologic state used to objectively measure processes in the body that occur during health, disease or in response to treatment. Researchers studying CFS have been looking for blood biomarkers so that diagnosis of CFS would not have to rely on self-reported symptoms like fatigue, pain and unrefreshing sleep that are difficult to measure by objective means. Finding a consistent and reproducible blood biomarker that could be turned into a clinical test would be a huge leap forward for care and credibility.
Powerful molecular tools have been developed that now allow the activity of thousands of genes to be examined at one time and to quantify how much gene activity there is by measuring the amount of message RNA (mRNA). More than 10 CFS studies have measured blood gene activity and found differences between people with CFS and healthy controls, showing promise of an objective blood test for CFS. However, even though investigators found differences between CFS subjects and healthy controls, there was little consistency between the 10 studies, making it difficult to use any of the identified gene activity differences as biomarkers.
In what could be a groundbreaking discovery for CFS, Alan R. Light, PhD, and his team at the University of Utah Health Sciences Center have identified genes that increase in activity following moderate exercise. The paper has been published in the Journal of Pain. These results as presented in this paper stand out as “smart science” for several reasons. First, the investigators’ logic is based on mouse experiments they conducted to understand sensory muscle fatigue and pain. These animal studies showed that there are molecular receptors that act together to detect the metabolites produced by muscle contraction. Second, the investigators used the findings from mouse experiments to develop a hypothesis for examining the blood in CFS patients and controls to look for activity of genes shown to detect metabolites that result from using muscles. Third, they used the kind of moderate, full-body exercise that is known to cause post-exertion fatigue in CFS but is well-tolerated by healthy control subjects.
The study included 19 CFS patients (15 women and 4 men) and 16 matched controls (11 women and 5 men). 68 percent of the CFS patients also met the criteria for fibromyalgia. Each subject was asked to exercise on an Airdyne bicycle (uses both arms and legs to turn the wheel) for 25 minutes. Blood was collected before exercise started and again at 30 minutes, 8 hours, 24 hours and 48 hours after exercise. Heart rate and perceived level of effort were monitored throughout the exercise challenge. The mRNA was extracted from the blood samples and gene activity was analyzed using the TaqMan Gene Expression Assays manufactured by Applied Biosystems, Inc.
In the laboratory they analyzed metabolite-detecting genes (ASIC3, P2X4, P2X5), adrenergic genes (A2A, B-1, B-2, COMT), and immune system genes (IL6, IL10, TNF alpha, TLR4 and CD14). When the investigators compared the activity of these genes before exercise, there was no difference between CFS patients and controls. But, as early as 30 minutes after exercise, there were significant increases in gene activity for the ASIC3, P2X4, P2X5 metabolite-detecting genes, the B-1, B-2 and COMT adrenergic genes, and the IL10, TLR4 and CD14 immune system genes. The gene activity increases persisted for up to 48 hours after exercise in the CFS patients. As anticipated with moderate exercise, there was no gene activity increase in the healthy subjects. The activity of these nine genes could be used to distinguish/identify most of the CFS patients from the control subjects.
These findings confirm previous studies that have found differences and disturbances in the immune system and the hypothalamic-pituitary-adrenal (HPA) axis and suggest that CFS patients have problems with sensory signaling. Importantly, this study suggests that a blood test for muscle fatigue and pain is possible. For these blood biomarkers to be validated, the numbers of CFS patients and controls will have to be expanded, and comparisons will need to be made against subjects with other fatiguing and painful conditions. The results reported in this paper were supported by a grant from the NIH. In late 2008, the Light team was awarded a grant from the Solve ME/CFS Initiative to expand the number of subjects and validate these blood biomarkers in other CFS patient populations. The Lights’ clinical collaborator is expert CFS clinician Dr. Lucinda Bateman of Salt Lake City.
(Updated January 19, 2010)
Suzanne Vernon, PhD, is the Association’s scientific director. She has nearly two decades of experience as a microbiologist.August 5, 2009