MicroRNAs in blood may help diagnose ocular MG, study suggests
Biomarkers distinguished patients from healthy people, those with early gMG
Three microRNAs (miRNAs) — small strands of RNA that regulate protein production — in blood samples accurately identified people with early-onset ocular myasthenia gravis (OMG) and distinguished them from early-onset generalized myasthenia gravis (gMG) patients and healthy people in a recent study.
“These results suggested that the three [miRNAs] have potential clinical application as OMG-specific biomarkers,” the researchers wrote in “Study of serum exosome miRNA as a biomarker for early onset adult ouclar myasthenia gravis,” which was published in Gene.
MG is an autoimmune disease caused by self-reactive antibodies attacking proteins involved in the communication between nerves and muscles, leading to muscle weakness and fatigue. Most cases are classified as either OMG or gMG based on clinical signs. Weakness that’s limited to eye and eyelid muscles marks OMG, while in gMG, a more severe and widespread form of the disease, muscle weakness isn’t restricted to any muscle group. A sizable proportion of OMG patients eventually progress to gMG, studies indicate.
OMG is often misdiagnosed as other disorders with similar manifestations. Thus, “it is necessary to identify more sensitive and specific biomarkers for the diagnosis and treatment of OMG,” the researchers wrote.
miRNAs in ocular MG
Normally, miRNAs regulate protein production by suppressing the function of messenger RNA (mRNA), the molecule that cells use as a template to make proteins. While emerging evidence indicates miRNA may predict the transition from OMG to gMG, it’s limited as a clinical biomarker because it rapidly degrades in blood samples.
Here, researchers investigated the potential utility of miRNAs within exosomes — tiny membrane-bound vesicles, or sacs, released by all types of cells that carry various biological molecules to facilitate cellular communication. Inside exosomes, miRNAs are protected from degradation.
Blood samples were collected from newly diagnosed OMG and gMG patients who had yet to be treated, along with age- and gender-matched healthy people who served as controls. Exosomes were isolated from blood serum, the liquid portion of blood that has no cells, and miRNA levels were analyzed.
The team found 27 miRNAs being produced at higher levels, or upregulated, in OMG patients compared with controls and 18 that were downregulated, or produced at lower levels. One miRNA was upregulated between OMG and gMG samples, and 21 were downregulated.
Across all the samples, five miRNAs overlapped — one (miR-130a-3p) was upregulated and four (miR-4712-3p; miR-6752-5p; miR-320d; miR-3614-3p) were downregulated.
The five miRNAs interacted with 408 mRNA molecules, each representing a unique gene. In OMG samples, these genes were primarily associated with two key biological signaling pathways called mTOR and Rap1.
The mTOR pathway plays an important role in immune responses. As such, “we speculate that the occurrence and development of OMG may also be related to the mTOR signaling pathway, which needs further exploration in the future,” the researchers said.
Three miRNAs as OMG biomarkers
The findings were validated in a second group, including 10 each with early-onset OMG and gMG, and 10 age- and gender-matched healthy controls. Three miRNAs — miR-320d, miR-4712-3p, and miR-3614-3p — were markedly downregulated in OMG samples compared with gMG and controls.
Finally, the area under the curve (AUC) was calculated for each miRNA. This type of statistical analysis yields values between 0 and 1, with higher ones indicating a greater accuracy of a specific miRNA at distinguishing OMG, gMG, and controls. In this analysis, if a specific miRNA had an AUC value greater than 0.7, it “was considered to have a high potential as a diagnostic marker.”
Results showed miR-320d had an AUC value of 0.78 when distinguishing controls from OMG patients. Similarly, miR-4712-3p and miR-3614-3p had an AUC value of 0.79. All three miRNAs had an AUC value of 0.84 when differentiating OMG and gMG patients.
“This work demonstrated that the expression [production] of serum exosomes miR-320d, miR-4712-3p and [miR-3614-3p] was decreased in early-onset OMG than GMG and [the] healthy control group, suggesting that they could be introduced as novel OMG-specific biomarkers,” wrote the researchers. “The diagnosis performance still needs to be further verified in a larger sample size.”