Cracks in the Dike? Researchers Question the Efficacy of the RNase L Fragmentation Test

The ratio of RNase L fragmentation is the closest thing to a biomarker we have in CFS. Studies from independent laboratories from around the world (U.S., Belgium, France, Japan) have indicated that a majority of CFS patients exhibit increased rates of RNase L fragmentation relative to healthy controls.
The road to widespread acceptance has not been easy, however. RNase L is a relatively recent discovery , and besides prostrate cancer, its connection with diseases is still unclear. Despite over 10 years of effort, much documentation and the publication of a book on RNase L dysfunction (‘Chronic Fatigue Syndrome A Biological Approach’) is either poorly treated or not treated in reviews on CFS immunology.

Two research groups have questioned the efficacy of the RNase L fragmentation test in CFS. This paper reviews the argument of the second.

Tiev, K., Briant, M., Ziani, M., Cabane, J., Demettre, E. and B. Lebleu. 2005. Variability of the RNase L isoform ration (37 kilodaltons/83 kilodaltons) in diagnosis of chronic fatigue syndrome. Clinical and Diagnostic Laboratory Immunology, Feb, 366.

A prior study by Tiev supported the contention that RNase L fragmentation is a suitable diagnostic tool for CFS. In a letter to the editor they report that further examinations indicated that the RNase L test had high variability and low reproducibility over time in CFS patients. In addition they reported that rates of RNase L fragmentation had little correlation with respect to fatigue scores over time.

The Tiev group examined RNase L fragmentation in 9 CFS patients over time and attempted to correlate RNase L fragmentation with Multi-Dimensional-Fatigue-Inventory (MFI) scores in 28 CFS and 24 healthy controls. Once a month for three months the 9 CFS patients and the healthy controls (number unknown) were tested twice for RNase L fragmentation. They found that correlation between the two samples was relatively low in the CFS group (.69, .69, .33) but was high in the control group (.95, .95, .95). When they compared the rates of RNase L fragmentation between months they found that the degree of RNase L fragmentation the CFS patients displayed varied greatly (.16. .14, -0.03).

Lastly the weak correlations (.14, .51, -0.3) between RNase L fragmentation and MFI fatigue scores suggested RNase L fragmentation did not play a major role in the fatigue found in CFS patients.

This paper suggests that while rates of RNase L fragmentation are high in CFS they bounce around a lot and may not be related the fatigue CFS patients experience.

Fremont, M., Vaeyens, F., Herst, C., Englebienne, P. and K. De Meirleir. 2005. 37-Kilodaltion/83-kilodalton RNase L isoform ratio in peripheral blood mononuclear cells; analytical performance and relevance for Chronic Fatigue Syndrome. Clinical and Diagnostic Laboratory Immunology, Oct, 1259-60.

Tiev, K., Cabane, J. and B. Lebleu. 2005. Authors Reply. Clinical and Diagnostic Laboratory Immunology, Oct, 1260.

In their letter to the editor, De Meirleir, Englebienne, and the employees of RedLabs had a response. The corresponding Tiev response follows theirs.

Fremont et. al noted the very small sample size of the fragmentation tests (n=9) and the potential for sampling error. (Sampling error occurs when such a small number of samples are collected that the researchers just happen to hit a unusual subset of them; in this case CFS patients with very high rates of RNase L variability.) Tiev agreed larger sample sizes are called for.

Fremont et. al. stated high rates of variability in the expected as the RNase L ratio’s rise because of the difficulty in scanning what’s left of the native RNase L enzyme. They noted that when 37/83 kDa ratio rises above 20%, the variability in readings is expected to exceed 30%. Thus the high variability in the RNase L test simply reflects difficulty reading it. They note the high consistency in the findings from the healthy controls.

Tiev noted the efficacy of the assay was not in question and that the large ratio’s Fremont et. al. expressed were not seen in their tests.

With regards to the poor correlation with fatigue scores Fremont et. al started that they were not surprising, given the complexity of CFS. Given the evidence that RNase L fragmentation is a function of proteolytic activity they note it probably better relates to levels of inflammation than to fatigue.

A recently completed study indicated RNase L fragmentation is very significantly correlated with levels of human leukocyte elastase activity (p<.001). Tiev agreed RNase L fragmentation probably reflected increased proteolytic activity that was indicative of an underlying inflammatory condition.

They suggest further study should concentrate on the cause of this proteolysis in CFS and in coming up with a better diagnostic test. Fremont et. al. noted the still relatively good diagnostic value of rates of RNase L fragmentation even given the high variability seen.

Editors Note: it’s good to hear of the new study involving elastase. Two processes are required for RNase L fragmentation to occur; the production of the 2-5A dimer that binds to, inactivates and renders RNase L vulnerable to proteolytic activity and increased rates of proteolytic activity.

Most RNase L research has concentrated on the first half of the equation, however, the cause of the increased proteolytic activity remains obscure. These papers certainly leave us in something of an odd position. The sample size most assuredly was very small and thus was vulnerable to sampling error.

On the other hand Tiev stated the high rates of RNase L fragmentation the Belgium group suggested responsible for the high variability were not present. If the RNase L test truly does exhibit such great variability over time does this suggest it is not central to CFS? The answer to this question may depend on the level at which it fluctuates; if it fluctuates between normal and high levels it may reflect an epiphenomenon in CFS.

If it fluctuates greatly in CFS but only at the higher ranges of fragmentation then it may very well be central to CFS pathology. It was hard to tell where it was at with this study; that rates of RNase L fragmentation were a good but not great diagnostic tool in this study suggested, however, it was mostly consistently higher.

The poor correlation with fatigue was surprising to me given that RNase fragmentation has been correlated with symptom severity in CFS before. The Belgium groups explanation was persuasive, however, as their recent study noted levels of an inflammatory protease, elastase, are correlated with rates of RNase L fragmentation.

The cause of the inflammatory state in CFS greatly needs to be elucidated. This layman concludes the Tiev study provides some cautionary signals regarding the RNase L test but its needs to be expanded in order to have greater validity. As we continue to learn more and more about RNase L we continue to refine its position in CFS. De Meirleir has stated that CFS is heterogeneous disorder; high rates of RNase L fragmentation are not found in all CFS but they do appear to occur in large percentage of them.

The validity of the test as a diagnostic tool still appears to be intact. Clearly more work needs to be done with regards to the tests variability over time, in identifying subsets of CFS patients with RNase L dysfunction and in delineating how levels of RNase L fragmentation in CFS patients compare to those in other diseases.

Share this!