By K. Kimberly McCleary, President & CEO
There has been a big break in the search for a robust biomarker that would help clarify the diagnosis of CFS and guide treatment decisions. Amid the current controversy over XMRV, a report published May 26, 2011, ahead of print in the Journal of Internal Medicine, has received scant attention. But its implications are huge, especially because it extends earlier reports from the same group with larger patient cohorts and more sophisticated subgroup analyses.
by the husband and wife team of Alan and Kathleen Light at University of Utah and clinical collaborator Lucinda Bateman, MD, concludes that “post-exercise increases for four genes meet published criteria as an objective biomarker for CFS, and could be useful in guiding treatment selection for different subgroups.” The study was funded by the CFIDS Association of America, the National Institutes of Health and the American Fibromyalgia Syndrome Association. Let”s take a closer look.
Patient Cohorts Studied
In this particular study, the research team identified three specific groups of individuals:
- FM-only: 18 patients who met American College of Rheumatology criteria for fibromyalgia (FM) (but did not also meet CFS or ME/CFS criteria and fatigue did not cause as much compromise of normal daily activities compared to the CFS/CFS FM group);
- CFS/CFS FM: 48 patients who met CDC criteria for CFS; 46 of these 48 (96%) individuals also met the Canadian clinical criteria for ME/CFS; 33 of the 48 (69%) also met criteria for FM; and
- Controls: 49 individuals considered “healthy” who did not meet criteria for FM, CFS, ME/CFS or several other conditions that would have excluded participation.
Of the CFS/CFS FM group of 48 individuals, 35 reported sudden onset with viral or flu-like symptoms. Five reported onset associated with another type of physical trauma (injury or fracture); 3 had onset associated with surgery and five could not associate the onset with a memorable event or illness. The CFS/CFS FM group was comprised of 33 females and 15 males and the racial make-up reflected the local population with 94 percent being Caucasian. Age and gender were well-matched for the CFS group and controls, but less well-matched for the FM group. The authors provide a detailed description of the medication use by each group (including controls) and later evaluate how certain medications, particularly antidepressants and anticonvulsants, may have affected the results reported.
All subjects provided assessments of mental fatigue, physical fatigue and pain severity using validated measurements at baseline and during and after the exercise challenge (described below). The CFS patients were also rated by Dr. Bateman for disorder severity on a scale of 1-4, with 1 being “house- or bed-bound with minimal activity tolerance” up to 4 for “able to do part-time school/work/other activities 10-30 hours per week but “nothing left over.”" Forty-five of the 48 patients were rated on this scale and the breakdown by severity was: four (9%) patients were rated 1 (most severe); 15 (33%) patients were rated 2; 20 (45%) patients were rated 3; and six (13%) patients were rated 4 (least severe).
The information collected about each of the subjects was used to examine the results by various subgroup analyses. Initially the investigators expected that separating the CFS group by the presence (or absence) of FM would provide meaningful subgrouping data, but this did not turn out to be the case. However, the FM-only group had distinctive results compared to the CFS/CFS FM and the controls.
All subjects in the study were asked to refrain from exercise activity greater than five minutes of walking for two days before and two days after the study visit. Testing was performed in the morning between 8 a.m. and 9:30 a.m. Blood was drawn at 5 time points: immediately prior to the test and at 30 minutes, 8 hours, 24 hours and 48 hours after the exercise task. Fatigue and pain symptoms were assessed before the challenge, at the mid-point and immediately after the exercise task and with each blood draw on a scale of 0-100, with 100 being the greatest level of fatigue or pain that they could imagine.
Based on the group”s pilot studies and other CFS-related exercise studies, they used a bike ergometer that required the use of both arms and legs to simulate 25 minutes of sustained moderate exercise. This format was selected because it was more similar “to the natural exercise experiences reported to exacerbate CFS symptoms in patients” daily lives,” compared to a shorter, more intense type of challenge called a “maximal exercise test” used in other studies. They report that the majority of the CFS and FM patients were able to complete the challenge and to attain 70 percent of the maximal heart rate level. “The very modest level of exercise for 25 minutes caused post-exertional malaise lasting 48 hours in all CFS and FM patient groups, but not controls.”
Gene Expression Results
Using real-time quantatative polymerase chain reaction (PCR), changes in messenger RNA (mRNA) gene expression were measured for each of the subjects at the 5 different time points. The technicians performing the PCR were blinded to the subjects” identities and group assignments. Candidate genes were selected on the basis of prior studies that showed their direct involvement in signaling fatigue by the skeletal muscle. These genes fell into 3 categories: sensory (pertaining to the body”s sensory nerve network), adrenergic (pertaining to the sympathetic nervous system and release of epinepherine) and immune.
There were no differences at baseline between the CFS/CFS FM group and the controls. At baseline, the FM-only group was distinguished by several differences. “They had significantly higher baseline quantities of mRNA for sensory receptors P2X4 and TRPV1 and for the cytokine IL10.” Based on the group”s earlier work in mice, they hypothesize that these markers represent increased signal for muscle metabolites that would lead to widespread increases in muscle pain and secondary hyperalgesia in skin throughout the body. The researchers were surprised that these levels did not change during the exercise challenge in this group; this was a novel finding.
Following the exercise challenge, the CFS patients showed greater increases in mRNA than controls for seven of the target genes. There was also a distinct separation into two groups within the CFS cohort based on the gene expression results. Thirty-four (71%) of the CFS patients had increases in the alpha-2A (α-2A) receptor at one or more time points following exercise, while 14 (29%) demonstrated large decreases in the same receptor. The larger subgroup showed large increases in eight genes but the smaller subgroup did not have signficant changes in any of these other genes compared to the control group. These changes observed in the subgroups were sustained immediately following exercise through 48 hours, as compared to controls.
Characteristics of Two CFS Subgroups
α-2A Increase Subgroup (34/48 CFS subjects): This group exhibited large gene expression increases after exercise in the following genes: P2X4, P2X5, TRPV1, α-2A, β-1, β-2, COMT and IL10. ”Interestingly, the genes found to be dysregulated in the present study represent most of the pathways hypothesized by others to be altered in CFS. These include the immune system (IL10 and leukocytes in general), cellular energy (P2X4 and TRPV1) and the cardiovascular system (α-2A, β-1, β-2 and COMT).” The group reports that none of these genes had been found by other groups using a single point-in-time blood draw to determine differences between CFS patients and controls (healthy and other diseases). “This is not surprising since the gene expression differences reported here were not observed at baseline but required moderate exercise to expose them.”
α-2A Decrease Subgroup (14/48 CFS subjects): The majority of this group (71%) also had clinical orthostatic intolerance and “suggests that different mechanisms cause the debilitating fatigue in this subgroup. The large decreases in α-2A may reflect a particular type of dysregulation of the sympathetic nervous system.” The researchers suggest that an effect of this dysregulation would be the “inadequate blood flow to the working muscles and the brain” that has been reported by other groups in some CFS subgroups. They state, “The relationship between α-2A decrease CFS patients and postural orthostatic tachycardia syndrome and the degree and type of autonomic disturbances needs further study.”
The two CFS subgroups did not differ by the fatigue/pain severity ratings before, during or after exercise challenge, by co-occurence of FM, disorder severity, antidepressant use or opioid use. The distribution of these features was similar in both groups. The evaluation of medication use in the two subgroups showed that there was a trend toward lesser post-exercise increases in selected genes among those CFS patients on anticonvulsants compared to those on no medications. “These findings suggest that anticonvulsant drugs may reduce the post-exercise gene expression increases in some CFS patients, but they also indicate that withdrawal from these medications prior to testing is not critical when attempting to differentiate their responses from those of healthy individuals.” This finding has important treatment implications.
The team reports that its analysis of the gene expression data has the potential to yield two biomakers — one for the larger subgroup of CFS patients and another for FM. “For the [larger CFS subgroup], a combination of PX4, α-2A, β-2 and IL10 at all time points after moderate exercise…would be considered a Very Good to Excellent diagnostic tool” based on published biomarker criteria. The reliability of the diagnostic value of decreased α-2A in the smaller subgroup was not possible to accurately compute because the number of patients in this subgroup was too small.
For FM, using P2X4, TRPRV1 and IL10 would be less ideal but would still identify the majority of FM patients. The substantial benefit of this test is that these differences were apparent at baseline and “a single blood draw could be used, and no exercise challenge would be required.”
- This study confirms the Lights” prior findingsthat “moderate exercise in CFS patients leads to increased expression of certain sensory ion channel, adrenergic and immune genes that do not occur in healthy individuals.”
- Exercise caused significant increases in all fatigue and pain measures at all time points during and after exercise in the CFS/CFS FM group. The FM group reported increases in pain and physical fatigue at all time points, but mental fatigue was not increased during and immediately after exercise. The control group did not report increased pain or mental fatigue at any point; physical fatigue was reported as being increased only at the mid-point of the exercise task.
- The group was able to demonstrate strong correlations between the ratings for fatigue and pain and the gene expression measures for P2X4, TRPV1, α-2A, β-2 and IL10.
- The target genes measured in this study were not selected to try to determine the cause of CFS or FM, but the authors note that the gene expression changes could be caused by viral infections. “…the increase in IL10 we observed at baseline in FM patients and in CFS following exercise is more similar to an enhanced Th2 [immune] response, which could potentially lead to greater susceptibility to viral infections and tumors.”
- The Lights (with other collaborators) have also been looking at other patient groups for some of the same markers. They have submitted another manuscript for publication that shows the gene markers reported in this study are not similarly increased in patients with multiple sclerosis. They have preliminary data indicating that they are not the same as patients with unexplained fatigue who have advanced prostate cancer.
- They have also looked at the possible overlap with depression. “Furthermore, the observations from this study on the subset of controls tested while on antidepressants prescribed for mild clinical depression suggest that these genes are not increased in medication-responsive depression; we are currently examining patients with moderate to severe medication-refractory depression to reinforce this tentative finding.”
- In the introduction to the paper, the authors cite a manuscript submitted that describes international consensus criteria for myalgic encephalomyelitis, listing the following authors: BM Carruthers, MI van de Sande, KL DeMeirleir, NG Klimas, T Mitchell, D Staines, AC Powles, DS Bell, R Vallings, and Speight. This may be the first public acknowledgement of a current effort to define criteria for ME.
This work has enormous potential for improving both the diagnosis and care of CFS and FM patients. The CFS subgroups identified may help to guide treatment and the possibility that anticonvulsants (like gabapentin or pregabalin) may dampen the disabling feature of post-exertional relapse is very promising. This study also adds strong support to the growing literature on the very real nature of post-exertional relapse itself, which may be beneficial not only to guide future research, but for legal matters such as documenting vocational disability. It demonstrates the benefit of looking for biologicial changes that occur as a result of the hallmark feature of post-exertion relapse. Finally, the preliminary work reported by the Lights to compare these findings to other disease states helps establish the utility of these markers to differentiate CFS not just from healthy individuals, but from other patient groups that exhibit disabling fatigue.
As with any research, these findings will need to be replicated by another research group in another group of CFS (and FM) patients. The fact that this work extends earlier similar observations provides hope that these findings will stand up to that test.
The CFIDS Association commends this team for its promising work and this important publication. We are grateful to our donors who supported our 2008 Campaign to Accelerate Research and the reviewers who ranked this project as highly meritorious on scientific and strategic criteria. We eagerly anticipate the additional publications promised in this manuscript and deeper insights that will lead to better understanding of CFS and better care for patients.
Light AR, Bateman L, Jo D, Hughen RW, VanHaitsma TA, White AL, Light KC. Gene expression alterations at baseline following moderate exercise in patients with chronic fatigue syndrome and fibromyalgia syndrome. Journal of Internal Medicine.2011 May 26. .
Drs. Kathy and Alan Light presented some of this data in a webinar held on October 5, 2010. You can view the slides and video recording. Please support research like this study through a gift to the CFIDS Association. We are putting research first to leverage and lead the collaborative research that will unlock the mysteries of CFS at the molecular, cellular and clinical levels.
K. Kimberly McCleary has served as the Association’s chief staff executive since 1991.
Note added: Dr. Alan Light describes the term biomarker and measures used to evaluate biomarkers in a a guest post here on Research1st: “Shedding Light on Biomarkers.”