- MicroRNAs are molecules involved in using the information in genes to produce proteins.
- A recent study explored their potential as biomarkers for ME/CFS by looking at differences in microRNA levels in the blood between 40 people with ME/CFS and 20 healthy control subjects.
- Compared with controls, people with ME/CFS had significant differences in the levels of four out of the eight microRNAs analysed.
- Furthermore, higher levels of microRNAs were related to more severe ME/CFS symptoms.
- Further research and larger studies are needed to validate and build on the findings of this relatively small study, to bring us closer to determining the diagnostic potential of microRNAs in ME/CFS.
Over the past decade, microRNAs (or miRNAs) have gained considerable attention for their potential as biomarkers in ME/CFS. These small molecules, found both inside and outside of cells, play a role in gene expression – the process of using information from sections of DNA, known as genes, to produce proteins that serve various functions in the body. To further investigate the role of microRNAs in ME/CFS, a recent study was conducted by Dr Irene Offritti and colleagues, with 60 participants recruited from an outpatient clinic in Latvia.
What was the aim of the study?
The primary aim of this small study was to assess whether there are differences in circulating microRNAs (i.e. in the blood or other body fluids) between patients with ME/CFS and healthy control subjects.
A secondary goal was to determine the human herpesvirus 6 (HHV-6) status of participants. HHV-6 is essentially a set of herpesviruses which has been proposed as one potential trigger of ME/CFS, and has been suggested to impact the expression of microRNAs.
As with similar research, the rationale for the study was to ascertain whether differences in microRNAs could be used to distinguish people with ME/CFS from healthy individuals, and therefore indicate that understanding microRNAs could move us a step closer to developing a diagnostic biomarker.
What were the methods?
The researchers recruited 40 patients and 20 healthy controls (without a medical history of ME/CFS) from an outpatient clinic in Latvia. It should be noted that whilst the paper consistently mentions ME/CFS, their clinical diagnosis was based on the Fukuda criteria, which actually refers to chronic fatigue syndrome (CFS). A semi-structured interview approach was used to categorise patients into three groups according to disease severity: mild, moderate and severe.
Extensive tests were performed on blood samples obtained from the participants. This analysis aimed to provide information about the types and levels of microRNAs and to detect the presence of HHV-6. The researchers focused on eight specific microRNAs (mir-124, mir-127, mir-140, mir-142, mir-143, mir-150, mir-448 and mir-551) which they thought were relevant based on previous literature.
The researchers also measured levels of pro-inflammatory cytokines (signalling proteins associated with inflammation), referring to previous links which had been made between them and HHV-6. Essentially, they were looking at the relationship between inflammation and microRNA levels in these patients.
What did they find?
The main findings of the study were:
- MicroRNA expression – Levels of three of the microRNAS analysed (miR-142, mir-150 and mir-448) were higher in people with ME/CFS than in controls, while another (miR-40) was lower in ME/CFS patients.
- Symptom severity – MicroRNA levels tended to be higher in patients who had more severe symptoms, indicating a potential association between microRNA expression and disease severity in ME/CFS. However, these findings were not always statistically significant, suggesting a need for further investigation.
- HHV-6 and pro-inflammatory cytokines – There was no significant correlation between microRNA levels and the presence of HHV-6 or levels of pro-inflammatory cytokines. This suggests that differences in microRNA expression are not directly associated with HHV-6 infection or the inflammatory status of individuals. However, the researchers did mention that the use of non-steroidal anti-inflammatory drugs (NSAIDs) and benzodiazepines could reduce levels of pro-inflammatory cytokines, thus making it difficult to draw firm conclusions.
The researchers mention that they used semi-structured interview questions by Minnock et al. to group patients according to disease severity. However, the reference article is not related to ME/CFS, rather it primarily addresses perceptions of fatigue in patients with rheumatoid arthritis. This raises a concern about the suitability of using these questions for ME/CFS classification, and it would be useful if the researchers had provided more information about their methods with respect to this.
The study refers to ME/CFS but uses the Fukuda criteria, which are specific to CFS and do not require the presence of post-exertional malaise, considered to be a cardinal feature of ME/CFS. This mismatch between the criteria and condition has potential implications on the validity of the study findings.
The researchers acknowledge that, not only did the study have a small sample size, but there were significant age differences between the patient and control groups. A small sample may not accurately represent a larger population and is more susceptible to being skewed by outliers or random fluctuations. Additionally, as the control group was not matched for age it makes it harder to draw firm conclusions as the differences in microRNA levels might have been age-related.
A quick glance at the summary table from a recent systematic review analysing potential ME/CFS biomarkers will tell you that an enormous number of microRNAs have been analysed, with minimal overlap between studies. Despite the limitations of this study, it is useful that the researchers chose to study microRNAs that they had noted in previous literature as this gives the opportunity to compare findings.
The three microRNAs increased in the patient group (miR-142, mir-150 and mir-448) were also found to be upregulated in previous data. However, they also mention that there are mixed results between studies regarding the expression of miR-140 and the presence of pro-inflammatory cytokines.
With the help of ME Research UK funding, researchers such as Dr Bhupesh Prusty and Dr Francisco Westermeier have also touched upon the relationship between ME/CFS and microRNAs. However, this is a vast and complex field, and we need larger studies with robust methodology to build upon and validate previous findings. At present it seems that quite a few more steps are needed before microRNAs could be considered a frontrunner in the search for biomarkers.