Biomarkers for Neuromyelitis Optica - An Overview

Introduction

Neuromyelitis optica spectrum disorders (NMOSD) is a group of rare autoimmune diseases of the central nervous system distinguished by periods of transverse myelitis, optic neuritis, and additional demyelinating assaults. NMOSD was once assumed to be a subtype of multiple sclerosis, but it is now recognized as a distinct illness with its mechanism, clinical course, and therapeutic choices. NMOSD primarily affects the optic nerves, the brainstem, and the spinal cord, posing unique obstacles to diagnosis and treatment.

This illness, which includes six syndromes, is closely related to aquaporin-4 immunoglobulin G antibodies (AQP4-IgG), and serologic testing is needed for a correct diagnosis. Neuromyelitis optica is an inflammatory demyelinating illness of the central nervous system that is distinct from multiple sclerosis. The search for biomarkers for neuromyelitis optica has continued over the past twenty years. To examine the primary research emphasis in this area, a bibliometric approach was employed.

Myelin oligodendrocyte glycoprotein-IgG is a clinical biomarker for myelin oligodendrocyte glycoprotein antibody-related illness. Recent biomarkers for neuromyelitis optica include cerebrospinal fluid immunological biomarkers that include glial fibrillary acidic protein, serum astrocyte injury biomarkers like the FAM19A5 gene, serum albumin, and gamma-aminobutyric acid (GAB).

The latest future clinical trials are investigating the potential of these biomarkers. Preliminary findings suggest that glial fibrillary acidic protein has emerged as a viable biomarker for neuromyelitis optica spectrum illness. Future studies aim to discover noninvasive biomarkers with high specificity, sensitivity, and safety levels for accurately diagnosing neuromyelitis optica.

What Is Neuromyelitis Optica Spectrum Disorder?

Neuromyelitis optica spectrum disorders impact 1–10 per 100,000 persons worldwide, spanning all ages and races, with females and people of Asian or African descent being the most commonly affected. A large number of NMOSD patients have a relapsing illness course, which causes disability over time due to partial recovery from recurring bouts. Despite recent advances in NMOSD treatment, there are no defined standards for who should be treated with immunosuppressive medicines and for how long, as recurrence can occur even after extended remission. There is an urgent need for clinically validated biomarkers that can help guide care and, ultimately, enhance the lives of NMOSD patients.

What Are the Symptoms of Neuromyelitis Optica Spectrum Disorders?

Neuromyelitis optica symptoms can result in blindness in either eye, weakness or paralysis in the legs or limbs, and severe spasms. Due to spinal cord damage, it can also induce sensory loss, excessive vomiting and hiccups, and bladder or bowel difficulties. Children may experience confusion, seizures, or comas.

What Are the Biomarkers for Neuromyelitis Optica?

An ideal illness biomarker is specific and sensitive, easy to sample using non-invasive procedures, and cost-effective to test. Biomarkers have important roles in improving diagnostic accuracy, predicting relapse, evaluating treatment responses, and determining the safety of treatment termination.

Despite its importance in the pathogenesis of NMOSD, AQP4-IgG is not an effective biomarker to monitor disease activity or therapy response. Laboratories use many methods to detect AQP4-IgG, and while a live cell-based assay is the gold-standard method, sensitivity and specificity vary significantly amongst tests, making it difficult to standardize the interpretation of titer data.

A few biomarkers include:

• GFAP and NFL as Diagnostic Biomarkers: Serum GFAP (sGFAP) and serum NfL (sNfL) have increased at baseline in NMOSD compared to healthy subjects, sGFAP is greater in AQP4-IgG-positive NMOSD compared to both multiple sclerosis (MS) and, to a lesser extent, MOGAD, implying that sGFAP, but not sNfL, may help distinguish NMOSD from other autoimmune CNS diseases. Notably, sGFAP levels do not appear to be as high in AQP4-seronegative NMOSD, implying that the fraction of clinical NMOSD patients who test negative for AQP4-IgG might have a distinct disease etiology that does not entail a main astrocytopathy. Both sNfL and sGFAP can remain elevated in remitted NMOSD compared to healthy controls. Still, sGFAP declines more quickly and to a greater extent than sNfL, which can remain elevated in NMOSD patients for months to years after relapse, indicating ongoing secondary damage to neurons long after the acute attack.

• GFAP and NfL as Attack Biomarkers: Another possible role for biomarkers of cellular damage is to monitor for NMOSD attacks and differentiate between accurate attacks vs. pseudo-attacks or to detect worsening symptoms despite the lack of new MRI-visible disease activity, particularly as a serum test would be faster and less expensive than repeated MRIs (magnetic resonance imaging). Even in clinically stable patients, increased sGFAP levels are associated with retinal neuroaxonal loss and decreasing afferent visual function, indicating greater subclinical chronic optic nerve damage.

• Neutrophil-To-Lymphocyte Ratio: Histopathologic samples of NMOSD lesions show an abundance of neutrophils, whereas MS lesions show higher macrophages and T-lymphocytes. The CSF neutrophil count is raised in roughly 60 % of NMOSD patients during acute attacks. The neutrophil-to-lymphocyte ratio (NLR) in blood is used as a biomarker in many disorders, including NMOSD.

• Cytokines, Chemokines, and T-Lymphocytes: Several cellular and humoral immune mediators play essential roles in NMOSD pathogenesis and are currently being investigated as possible biomarkers. IL-6 serves various roles in NMOSD, including encouraging the survival of plasmablasts that release AQP4-IgG.

• Other Biomarkers: Numerous new NMOSD biomarkers have been proposed in addition to the broad types previously covered. Adhesion molecules are dysregulated in NMOSD; they are essential in the disruption of the blood-brain barrier that results in the migration of peripheral immune cells as well as antibodies into CSF (cerebrospinal fluid).

Conclusion

Many intriguing biomarkers have the potential to significantly enhance the care of NMOSD patients throughout the disease. Although many of the biomarker discoveries mentioned here are encouraging, much more work must be done before these biomarkers are generally recognized in clinical practice.

Some biomarkers have been explored using older detection techniques, such as immunoblot and ELISA (enzyme-linked immunosorbent assay), while more recent studies have used newer technologies, such as single-molecule arrays (SIMOA). It is unclear how the results will transfer across detection modalities. Furthermore, as therapy choices for NMOSD proliferate, research must carefully assess the implications of various medications on biomarker interpretation.