Neuromyelitis Optica (NMO) is an autoimmune disease that affects the central nervous system (CNS). It preferentially targets the spinal cord and optic nerves, but may also attack the brain. Common symptoms include blindness in one or both eyes, weakness or paralysis in the extremities, and impaired function of the bladder and/or bowel. Once thought to be a variant of multiple sclerosis (MS), NMO is now recognized as a distinct disorder. Unlike MS, disability in NMO accumulates with each successive relapse.
The primary mechanism for cellular damage in NMO is the autoimmune attack of the astrocytic aquaporin 4 (AQP4) protein by AQP4-IgG antibodies (Ab). AQP4 is a water channel protein responsible for the transport of water and small solutes across the membrane. In NMO the body erroneously produces Abs that block or destroy the AQP4 proteins present in the spinal cord, eyes, and brain, initiating lesions and ultimately resulting in neuronal death. Over time, these damaged and dead neurons can produce severe deficits. Lesions produced by AQP4 antibodies tend to appear in the cervical region of the spinal cord, some of which extend into the brainstem region.
AQP4-IgG Abs are 500 times more concentrated in plasma than in cerebrospinal fluid (CSF). This implies that they form peripherally and then enter the CNS. Once inside, they produce a cascade of inflammatory events, producing damage and causing further disruption of the blood-brain barrier.
Anti-AQP4 Live Cell-Based Assay (CBA)
Assays based on live transfected cells have been shown by systematic review to be the most sensitive assays available for detection of AQP4 Abs. BC Neuroimmunology is presently the only organization to offer live CBAs for anti-AQP4 antibodies in Canada.
Tests Available for Research Purposes Only
While ~65% of patients with Neuromyelitis Optica spectrum disorders (NMOSD) are positive for AQP4 antibodies, approximately 5-10% of NMOSD patients show seropositivity instead for myelin oligodendrocyte glycoprotein (MOG) antibodies. MOG is considered to be an adhesion molecule that provides structural integrity for the myelin sheath. Anti-MOG Ab attack causes similar inflammation of the optic nerve (optic neuritis) and/or spinal cord (transverse myelitis). Direct damage to the myelin sheath of neurons can also occur. MOG neuritis usually affects only one eye. MOG antibody attack tends to yield long lesions extending to the lumbar section of the spinal cord.
Despite the low representation of MOG Abs in the overall clinical picture of NMOSD, a higher percentage of patients (~20%) assessed as seronegative for AQP4 Abs display elevated titres for MOG Abs. It should be noted that MOG antibodies have also been reported in a variety of other demyelinating diseases, including MS and acute disseminated encephalomyelitis (ADEM), and can even be seen in healthy patients.
CBAs for anti-MOG Abs have been demonstrated in numerous blinded studies to be the most effective, state-of-the-art means of detection for anti-MOG Abs. Accreditation for our anti-MOG Ab CBA is pending.
BC Neuroimmunology Laboratory Requisition Rev 5.0 – November 2022
*Download the requisition onto a computer and open with Adobe Acrobat/Reader for a writeable PDF.