This paper looks at the general trends in CFS research over the year, highlights the ‘Paper of the Year’, and summarizes the top 10 research papers.

According to PubMed (and including the Journal of Chronic Fatigue Syndrome) about 126 papers were published on CFS in 2005. This was about a 15% drop from 2004 but is about average for the past five years (Click here). A division of the papers into several general categories indicates that the immunology and psychology are still the primary research interests in CFS and there is moderate interest in the brain, endocrine system and the metabolism. The clinical aspects of CFS (diagnosis, prognosis, definition, treatment programs, controversy) continue to be an areas of great interest.

Is this a sufficient number to move the field of CFS research at an acceptable pace? Given the multi-systemic nature of the problems in CFS, our still woeful ignorance of its pathophysiology, and the widely varying range of these studies, from small to large, from complex to relatively simple, it does not appear so. Consider the eight categories the research into CFS was broken into at the start of this paper (immune, brain/CNS, etc.). Each of these can be divided into multiple subcategories and each of those subcategories can be divided further. For example, areas of interest in the immune system include natural killer and T-cell functioning, cytokine activity (TNF-a, IL-1, IL-6, IL-10, TGF-b, interferon), cytokine and other polymorphisms, RNase L fragmentation, apoptosis, PKR activity, CD marker prevalence, viral reactivation (EBV, HHV-6, enteroviruses, HERV’s), bacterial prevalence (mycoplasma, chlamydiae, Borrelia), not to mention the complex field of neuroendocrine interactions and the mechanisms of post-infective fatigue. Given sufficient funding we could easily have had 30 or more studies on the immune system alone. Instead we had 13 many of which had quite limited aims.

In addition many topics of interest to physicians such as detoxification capabilities, toxin levels, Lyme disease frequency, etc. have never been studied in CFS. It seems remarkable given the interest in Lyme disease in general and post-infective fatigue specifically in CFS that no studies have attempted to assess Lyme disease frequency in CFS. Similarly despite the increasing interest in the cardiovascular health of CFS patients no studies have focused on this topic for several years now. This is the kind of problem that guarantees that the progress in most areas of CFS research will be incremental and slow and suggests that, short of a sudden breakthrough, many CFS patients may not see a resolution or even significant remediation of their symptoms for many years to come.

The continuing high number of studies focused on issues other than CFS pathophysiology indicates that in a world of limited resources many are essentially being wasted. The focus on issues other than CFS pathophysiology represents an enormous resource drain few other diseases have to cope with.

Despite the low number of studies examining CFS pathophysiology, CFS researchers made good use of what they had; this was a very good year for CFS research.

One paper every year is chosen as Paper of the Year. This year it went, not surprisingly, to a potentially groundbreaking paper on the brain.

The high concentration of notable studies on the brain made 2005 the ‘The Year of the Brain" While the brain/CNS receives fewer studies than does the immune system, it appears to be a more potent arena of research right now.

Creating a distinction between these research areas may, however, be misleading. The fatigue in CFS may be ‘central’, i.e. located in the brain, but it could be triggered by infections originating in the body. A recent study that followed a cohort of infectious mononucleosis (IM) patients over time concluded that CNS irregularities probably determined which patients recovered from IM and which progressed to CFS. These researchers are now using imaging studies to examine brain functioning in the IM/CFS patients and controls. The National Institutes of Health (NIH) recently provided a large grant to study neuroimmune mechanisms of CFS. The frequent highlighting of neurological, immune and signaling genes in the gene expression studies also suggests the neuro-immune interface may be impaired in CFS.

The Baraniuk paper examined the protein expression present in the cerebrospinal fluid of CFS, FMS and GWS patients. Intriguingly, the proteins present in each of the groups were similar enough for them to be combined into one group.

One very positive aspect of these findings was their coherence. Unlike some gene expression studies where investigators have been at something of a loss, given the disparate activities of the unusually expressed genes, to explain their results, these researchers were able to easily outline a pathological process involving the proteins they found highlighted in the CFS patients. They posited that a brain injury (oromuscoid proteins) causing bleeding (heme scavenger proteins), possibly due to extracellular protein accumulations (gelsolins) in the blood vessels, prompted the release of anti-hemorrhage factors (PDEF) and central nervous system repair proteins (Behabs). In effect they posited that a process of protein aggregation (or a cerebral amyloid angioopathy (CAA)) was occurring in the brains of CFS patients.

Cerebral (brain) amyloid (type of protein) angiopathies (disease of the blood vessels) (CAA’s) make up a large group of conditions characterized by protein misfolding, protein deposits and a consequent weakening of the blood vessels that can result in everything from microhemorrages all the way to cerebral infarctions. Since the endothelial cells lining the blood vessels play a critical role in maintaining the blood brain barrier (BBB) amyloid deposition on them can also lead to increased permeability of the BBB and pathogen, cytokine, etc. and further protein leakage into the brain. Injury to the blood vessels can also lead to an inflammatory reaction resulting in macrophage infiltration and a vasculitis (inflammation of the blood vessels). Where do these proteins come from? Most evidence points to the neurons. We will later see evidence suggesting neuronal volume is reduced in the brains of CFS patients.

Possibly the most significant outcome of this study was the development of a proteome ‘biosignature’. A statistically produced model indicated that the presence of any one of five proteins (keratin 16, @-2-macroglobullin, orosomucoid-2, autotoxin, pigment epithelium-derived factor) differentiated ‘CFS’ patients from controls with a high degree of confidence.

This study established a number of firsts. It was the first proteomic study done in CFS, the first gene or protein expression study to examine the cerebral spinal fluid (CSF), the first gene or protein expression study to come up with a putative biomarker (proteome), the first study to suggest a common source of CFS, FMS and related diseases, and the first gene or protein expression study to suggest an integrated pathophysiological model for CFS. In one swoop this paper may have reoriented thinking on brain dysfunction in CFS.

With all its positive aspects these findings were preliminary and need to be replicated. Still, the coherence of the findings suggests Baraniuk and his team may have uncovered an important part of CFS pathophysiology. Indeed, they felt confident enough of their findings to state at the end of their paper that this

"proteomic model provides initial objective evidence for the legitimacy of CFS as a distinct neurological disease".

For more on this study click here.

Although neuropsychological tests have provided little support that the cognitive processes in CFS are significantly impaired, CFS patients often assert that their thinking is much more effortful and that they think less well. This study appears to have found a way to reconcile these two seemingly contradictory claims.

In order to efficiently process verbal information, one’s working memory needs to be intact. The model of working memory posits that verbal information is first encoded and temporarily stored and then manipulated and utilized by something called the ‘supervisory attention system.’ This encoding process is believed to take place in the prefrontal cortices and the anterior cingulate.

In this study Dr. Lange used an fMRI to assess patterns of brain activation in CFS patients with and without documented cognitive problems and in healthy controls. Her group posited that inefficient information processing in CFS patients would require them to use more parts of their brain to carry out a task than would the healthy controls. That is exactly what they found.

While healthy controls needed to activate the dorso and ventrolateral prefrontal, supplementary motor and premotor regions in the left side of the brain, the CFS patients with cognitive problems had to activate these areas on both sides of the brain. Even CFS patients without cognitive deficits needed to engage more areas of the brain than did the healthy controls. To underscore the magnitude of the differences found, Lange stated that the CFS patients displayed patterns of altered brain activation similar to those seen in individuals with traumatic brain injury and multiple sclerosis.

Some have suggested that the increased mental effort associated with CFS has a psychological basis but Dr. Lange demonstrated that these brain abnormalities were associated not with the presence of a mood disorder but with the degree of mental effort exerted, i.e. CFS patients have to devote more effort to thinking not because they are so focused on their symptoms but because they have to activate more parts of their brain.

Could something as fundamental as the volume of the brain be reduced in CFS? Studies of brain volume are notoriously unreliable but these researchers used an automated scanning device that took the subjectivity out of this process. They used this scanning device to look at gray and white matter volume in the brain. Gray matter is composed of the actual cell bodies of the neurons, while white matter is made up of the filaments that connect them.

This study found the connectivity in CFS patients brains was intact but that the volume of the nerve cells was reduced quite significantly (p<.001.)

Neither the cause nor the consequences of the disappearing neurons was clear. Reduced neuron cell numbers could occur because of increased neuron cell death or decreased nerve cell replacement. A study showing that aerobic exercise in the elderly lead to increased nerve cell production suggested that the low activity levels in CFS could result in impaired nerve renewal. Indeed, activity measurements in the CFS patients revealed that the patients with the most reduced brain volumes were the least active. On the other hand, this scenario would suggest more and more progressive gray matter loss would occur over time, but illness duration was not correlated with gray matter loss in this study.

Dr. Lange is continuing her studies of gray matter volume loss in CFS(click here).

A neurotransmitter and vasoconstrictor found in the central nervous system and bloodstream, serotonin is present in relatively high concentrations in some areas of the central nervous system (hypothalamus, basal ganglia) that some researchers are involved in CFS (click here). High central nervous system (CNS) serotonin levels could cause many of the symptoms present in CFS including poor sleep and reduced motor performance and endurance and can alter, interestingly, ones ‘psychological perception of fatigue’. Some believe that high brain serotonin levels produce the fatigue one experiences during intense exercise.

The first clue that serotonin (5-HT) levels might be abnormally high in the brains of CFS patients came in 1992 when increased levels of 5HIAA, a metabolite of serotonin, in the cerebral spinal fluid were found. Since then several studies have found evidence of either increased or decreased brain serotonergic activity or increased 5-HT1A (serotonin) receptor sensitivity.

This study found that reduced serotonin receptor (5HT1A) binding occurred throughout the brain and was centered in the hippocampus, a region of the brain involved in learning and the stress response. Cleare proposed that the reduced serotonin binding potential found compensated for chronically high 5-HT activity. Cells often compensate for high (or low) levels of neurotransmitter by reducing (or increasing) the amount of receptors that respond to them. Thus the problem appears to be high not low serotonin levels in the brain.

Cleare, a psychologist, noted that similar levels of reduced receptor binding potential also occur in depression and panic disorder and suggested that reduced serotonin receptor activity could be a risk factor both for depression and CFS. Indeed, Cleare posited that reduced serotonin receptor activity could influence a wide variety of characteristics including personality, goal oriented behavior, sleep, pain and sexual activity, among others.

Almost twenty years after CFS burst on the scene we still have no biomarker, we still battle against psychological paradigms and, of course, we are still burdened with this lousy name. CFS patients have hoped that the gene expression studies will, like manna from heaven, provide a biomarker, stimulate exciting new research areas and provide new treatment options; in short, that they will lead us to the promised land.

Given their expectations CFS patients have awaited the results of these expensive studies with much hope and not a little anxiety. In the face of such high expectations the UK CFS research group MERGE, while continuing to help fund these studies, reminded CFS patients that their expense and complexity precluded them from being quick fixes. Indeed, the results from the first gene expression studies were not particularly impressive as only limited numbers of often quite disparate genes were highlighted. Piecing the results together to form a coherent model of CFS appeared to be rather problematic. Then came the CDC Vernon exercise study¼

Although it was not large (3800 genes, @15% of the genome) this was the first gene expression study to analyze gene expression patterns in CFS patients and healthy controls before and 4 hours after exercise. Its results appeared to be particularly compelling given the central role post-exertional fatigue appears to play in many CFS patients. This aspect of CFS is rarely studied; in this case it reaped dividends.

In a finding the authors characterized as ‘dramatic’, this study found that the expression of over half the 21 genes (n=11) differentially expressed in the healthy controls after exercise did not change in the CFS patients. This suggests that a significant portion of the genetic activity needed to successfully recover from physical activity simply does not occur in CFS patients.

What kind of activity were these genes engaged in? Another gratifying result was the functional coherence that these genes displayed. Almost half of this ‘missing’ gene activity concerned in transportation of substances in and out of the cell. A class comparison indicated that biological pathways involving ion channel transport, ATPase activity and transmembrane transport (n=129 genes in total) were altered in CFS. Interestingly some difference was present before exercise (n=82 genes) but it was accentuated after exercise (n=129 genes).

In some ways this pattern was not surprising. After all, ion channels play a critical role in every step of muscular and nervous system activity. Several nervous system channelopathies, predominantly affect muscle activity. As noted in ‘A Neurological Channelopathy in CFS? (click here)’ there is considerable symptom overlap between some of these neurological channelopathies and CFS.

Two research groups (Chaudhuri/Behan, De Meirleir/Englebienne) have theorized that ion channel dysfunction could be central in CFS but they have, for the most part, been voices in the wilderness (See A Channelopathy in CFS?). To have the CDC of all institutions provide some validation for their theories must have been gratifying on any number of levels.

In the past Dr. Kerr has focused his attention on immune system alterations in CFS. To this end he pioneered work that illustrated that not only do a subset of people with parvovirus B19 infection come down with CFS but that long-standing cytokine dysregulations appear to contribute to their illness. Now he has turned his attention to gene expression in CFS.

This study of 9522 genes (approx. 1/3^rd genome) found that CFS patients could be differentiated from healthy controls using the expression of 16 genes involving neuronal, immune, or ubiquitous cellular processes active at various locations in the cell. Attempting to draw a coherent picture of these widely varying genes, however, appeared to be difficult; the Kerr group stated that the ‘involvement of genes from several disparate pathways suggests a complex pathogenesis’. Nothing is simple in CFS!

While the patterns of abnormal gene expression were complex they at least made sense given what we know about CFS. For instance, the NTE gene found upregulated in this study is targeted by organophosphates and may relate to neuronal problems (and MCS?) in CFS. Several genes involved in mitochondrial activity could help explain the fatigue in CFS, and one gene, EIF4F, that is often hijacked by viruses, could provide a bridge between immune dysfunction and poor energy production in CFS. Similarly the genes involved in immune activation could help explain signs of immune dysfunction in CFS.

Dr. Kerr appeared to be quite confident about his findings. In The New Scientist he said his team’s findings indicate that ‘a significant part of the pathogenesis resides in the white blood cells’ and that this new data ‘will open the door to the development of pharmacological interventions’. Dr. Kerr may feel confident about his results because of the unusual rigor of the study. The microarray results were double-checked using real time PCR to ensure the mRNA they thought they were seeing was actually there.

The most important thing about this study, though, is not what’s in it but what it’s given birth to. The results were sufficiently encouraging for the Kerr team to embark on a much (much!) larger, more comprehensive study that reportedly contains a thousand CFS patients! The early reports from this new study indicate the results are consistent, so far, with the old study, and that he is finding protein analogues for the gene expression data. Finding proteins that fit the genes not only validates the gene expression findings but may also provide possible biomarkers for CFS. Finally, Dr. Kerr is reportedly beginning a treatment trial based on his gene expression results to test the effectiveness of interferon B. We have much to look forward to from Dr. Kerr.

While the CFS research efforts have often been dogged by heterogeneous and sometimes even conflicting findings, the results of studies into the levels of oxidative stress levels (i.e. free radical activity) in CFS have been notably consistent. Indeed it is remarkable how many different areas of the body (red blood cells, serum, blood, muscles and indirectly the brain) have displayed increased oxidative stress in CFS patients.

Why are free radicals so important? Because they can do so many bad things. Free radicals – unbalanced molecules that either grab electrons from or push electrons onto other molecules – are highly attracted to the fats in cellular membranes surrounding the cell and the mitochondria and to the DNA. Besides altering important ‘biophysical’ properties as membrane fluidity, free radicals can impair cell functioning by inactivating receptors or enzymes or ion channels on the surface of the cell or by modifying critical biomolecules in the cell. Free radical activity can occur in every part of the body but is especially pronounced during exercise and immune activation.

This study, employing a particularly ironclad methodology, appears to have put a cap on the question whether oxidative stress is increased in CFS patients. The main finding was that CFS patients display significantly higher levels of oxidation products called F2 isoprostanes in their blood than healthy controls.

No one knows exactly what roles the F2 isoprostanes play in CFS but the list of possible effects is long. When F2 isoprostanes bind to the receptors in the endothelial cells lining the blood vessels they cause the blood vessels to vasoconstrict (narrow) and have been shown to reduce blood flows to the brain, heart, lungs and eyes. The authors note they could contribute to several conditions in CFS including postural tachycardia syndrome (POTS) or the cardiovascular problems found in some CFS patients.

This study went beyond simply characterizing the state of oxidative stress in CFS. An examination of the lipid profiles of CFS patients found that they also had significantly increased levels of the ‘bad’ cholesterol (oxidized low density lipoprotein - oxLDL), and low levels of the ‘good cholesterol (HDL) relative to the healthy controls. Because LDLs transport cholesterol to the tissues high levels of LDLs can result in high cholesterol levels. Even at low levels OxLDL particles are toxic to the endothelial cells lining the blood vessels and can promote clogging of the blood vessels. In contrast HDLs transport cholesterol from the tissues to the liver and have protective effects on the heart.

CFS patients then have something of a double whammy! While their HDL cholesterol levels are not near the levels associated with atherosclerosis they are still significantly lower than those found in healthy, age and sex matched controls. They have lower levels of the compound (HDL) used to transport cholesterol levels away from the tissues but higher levels of the toxic form of LDL that transports cholesterol to the tissues. This, and the high isoprostanes levels, suggests they are at risk for oxidative processes that damage the blood vessels.

But where does the increased oxidative stress originate from? The authors suggested three processes: muscle pathology, immune activation and environmental toxins. They stress that since CFS is a heterogeneous disorder any of the three may be present in a particular CFS patient. One of these is explored in the next study. In something of a warning statement the authors noted that CFS patients have a lipid profile and oxidant biology that is consistent with ‘cardiovascular risk’ and suggest antioxidants may be helpful. They noted that obesity presents ‘a potential additional burden to free radical formation and CFS pathology’. For a more in depth analysis of this study click here.

Although CFS patients have long complained of their impaired ability to a) exercise and b) recover from exercise, the evidence for muscle pathology in CFS has been mixed. While studies have found reduced blood flows to the muscles they have not usually found evidence either of altered muscle metabolism or of overt structural damage.

A recent study, however, found impaired ion channel (Na+/K+, Ca ATPase) activity in the sarcoplasmic reticulum of muscle cells in CFS patients. The sarcoplasmic reticulum controls calcium concentrations in muscle cells and thus muscle contraction Some studies also indicate that a subset of CFS patients have impaired aerobic metabolism and increased lactate production. In addition since many free radicals are produced during exercise the finding of increased oxidative stress in CFS places a spotlight on muscle activity. We have, of course, just seen that Kennedy et. al. propose that muscle pathology could be the cause of the increased oxidative stress levels they observed.

In this study, the most complete yet on the dynamics of muscle activity in CFS patients, muscle activity was examined from three different angles; muscle metabolism, oxidative stress and neuromuscular excitability.

Like most others before it this study found no indication of impaired muscle metabolism or increased blood acidosis. Similar resting levels of TBARS, a free radical product, ascorbic acid (vitamin C) and glutathione (GSH) suggested that neither CFS patients nor the healthy controls exhibited increased oxidative stress or depleted antioxidant levels at rest. While the control patients displayed no changes in the amplitude or duration of what is called the ‘M-wave’, the CFS patients displayed a significantly lengthened M-wave starting five minutes after the completion of the exercise and persisting for 30 minutes (the limit of the observation period). Since the M-wave is a measure of muscle excitability this suggests prolonged muscle excitability (contraction?) in CFS.

Levels of oxidative stress also appeared much earlier in CFS patients and lasted longer, and to boot, the levels of ascorbic acid, the antioxidant most implicated in muscle protection, were greatly depleted in CFS patients in the post-exercise period. Thus this team found several indications of post-exercise muscle pathology in CFS patients.

The authors posited that increased levels of oxidative stress in the muscles of CFS patients depleted ascorbic acid levels and caused the abnormal findings in the post-exercise period. They noted that a prior study by Fulle suggested that increased free radicals in CFS patients impaired sarcoplasmic reticulum functioning. Both studies, therefore, were able to link increased oxidative stress in CFS patients with impaired muscle functioning. The authors did not speculate why the muscles of CFS patients would pump out more free radicals than normal.

Could the mysteries of post-exertional fatigue finally be yielding to analysis? These researchers’ ability to link abnormalities in the post-exercise period to oxidative stress was exciting given the uniqueness of the post-exertional fatigue symptom in CFS. The researchers at MERGE are currently attempting to replicate this study.

Epstein Barr virus (EBV) was the first big disappointment in CFS. Although early studies suggested EBV might cause CFS later studies suggested otherwise and research into EBV and CFS waned greatly. The idea, therefore, that an undiagnosed EBV infection could cause CFS in some people is controversial to say the least. A research group headed by the Ronald Glaser, however, asserts that the research community has largely missed the boat on EBV and CFS.

Glaser et al. believes the immune system is about half-way effective in CFS. They posit that CFS patients are able to largely inhibit EBV from replicating but are unable to shut down EBV activity early in its life cycle when it is producing several enzymes (DNase, DNA polymerase, dUTPase) that have immune system altering capabilities. They argue that since traditional antibody tests measure antibodies produced to antigens produced after this period that they can miss signs of EBV activation. Traditional EBV antibody tests measure antibodies to protein complexes produced late in EBV’s life cycle as it forms a protective cap around its DNA. Researchers have found that antibodies to early EBV enzymes are expressed in a number of diseases including HIV. The presence of antibodies to the early EBV enzyme dUTPase in chronic EBV infections suggests it may contribute to chronic illness.

This is not a new theory - it’s simply a poorly studied one. Jones and the Glaser first found a relationship between CFS and antibodies to these enzymes in 1988, and suggested that the dysregulated cytokine production and impaired T-cell activity found in CFS patients could be due to the immune system reacting to the early EBV enzyme DNase (Jones et al. 1988). A small 1991 study found DNase was expressed in all six CFS patients. Another 1994 study found antibodies to early EBV enzymes in CFS patients (Natelson et al. 1994). Glaser at al. report that recent data indicates a large number of CFS patients (41-83%) test positive for antibodies to enzymes produced early in EBV’s life cycle. Some researchers now believe that the natural killer cell ‘burnout’ seen in CFS patients is also due to the presence of a chronic infectious state (Click here). 

There could also be a tie-in here with an impaired stress response in CFS. Stressors have been shown to induce the production of early EBV proteins (enzymes). When mice infected with another herpesvirus (CMV) were subjected to an immune stressor (TNF-a), they were found to produce only early EBV proteins. There is evidence of increased TNF-a levels in CFS. Several studies indicating that increased stress levels are present in some CFS patients just prior to disease onset suggest they may have been at risk for EBV reactivation.

We do not appear to be through with EBV. Glaser’s, Lerner’s and Lloyd’s studies all suggest that one way or another EBV may very well play an important role in at least a subset of CFS patients. An upcoming paper will the possible roles EBV may play in CFS.

On the negative (?) side we have seen studies suggesting that neither orthostatic intolerance or hypercoagulation commonly occurs in CFS. We are still waiting on the results of the 5-year Hurwitz red blood cell/low blood volume study, the Gow whole genome gene expression study and the Peckerman systolic function study.

CFS patients can take comfort from the successful studies and interesting findings from last year – one gets the sense that CFS researchers are getting a better feel for CFS and have begun to hone in on some central factors in it. Given the complexity of CFS and the scope of the problems confronting CFS researchers, however, one can only characterize the pace of CFS research as far too slow. The dominant trends of CFS research - the inadequate funding, the diversion of precious funds to psychological studies, the lack of overall organization, the problems with the definition, the problems with subsets, the piecemeal efforts by small scattered research groups – remain and will continue to hinder the pace at which CFS is understood. Still one can only come away from 2005 with more optimism for what the future holds.