Myelin Oligodendrocyte Glycoprotein (MOG) & MOG Antibody-Associated Disease (MOGAD)

🔎 About

• Myelin oligodendrocyte glycoprotein (MOG) is a minor myelin protein expressed on the surface of oligodendrocytes and on the outermost layer of central nervous system (CNS) myelin sheaths.
• It is a type I transmembrane glycoprotein with a single extracellular immunoglobulin-like domain, making it highly accessible to circulating autoantibodies. :contentReference[oaicite:0]{index=0}
• The MOG gene lies on chromosome 6p21.3–p22 within the major histocompatibility complex region and is highly conserved across species, suggesting an important structural role in myelin stability. :contentReference[oaicite:1]{index=1}
• Physiologically, MOG is thought to contribute to completion and maintenance of compact myelin and to myelin–axon adhesion, rather than primary conduction itself.

🧬 Pathophysiology – Why is MOG Immunologically Important?

• Because its Ig-like domain is exposed extracellularly, MOG becomes an easily accessible target for pathogenic IgG autoantibodies.
• In MOG antibody-associated disease (MOGAD), these antibodies bind MOG and trigger complement activation, inflammatory cell recruitment, and demyelination within the optic nerves, brain and spinal cord. :contentReference[oaicite:2]{index=2}
• The pathology appears more “perivenous and inflammatory” than classic multiple sclerosis (MS), often resembling acute disseminated encephalomyelitis (ADEM) rather than confluent MS plaques on histology. :contentReference[oaicite:3]{index=3}
• Unlike AQP4-IgG neuromyelitis optica spectrum disorder (NMOSD), MOGAD is primarily an oligodendrocyte/myelin disorder (rather than astrocytopathy), which helps explain differences in imaging and clinical course.

🧾 Definition – What is MOGAD?

• MOG antibody-associated disease (MOGAD) is an inflammatory demyelinating disease of the CNS characterised by:
  • a typical acquired demyelinating syndrome (e.g. optic neuritis, myelitis, ADEM, brainstem or cortical encephalitis), and
  • serum MOG-IgG positivity detected with a live cell-based assay targeting the extracellular domain of human MOG. :contentReference[oaicite:4]{index=4}
• The 2023 International MOGAD Panel criteria emphasise:
  • Use of a validated cell-based assay,
  • Exclusion of MS and AQP4-IgG NMOSD, and
  • Cautious interpretation of low-titre or transient MOG-IgG, especially if the phenotype is atypical. :contentReference[oaicite:5]{index=5}
• MOGAD can be monophasic or relapsing, with relapse risk higher in the first few years after onset.

📊 Epidemiology & Clinical Patterns

• MOGAD is rare but is now recognised as one of the more common antibody-mediated CNS demyelinating disorders, affecting both children and adults. :contentReference[oaicite:6]{index=6}
• In paediatrics it frequently presents with ADEM or multiphasic ADEM; in adults it more often causes optic neuritis (often bilateral) and transverse myelitis. :contentReference[oaicite:7]{index=7}
• Common clinical presentations:
  • Optic neuritis – visual loss, pain on eye movements; often bilateral and with marked optic disc swelling.
  • Transverse myelitis – paraparesis or quadriparesis, sensory level, sphincter disturbance; lesions can be longitudinally extensive but may be shorter than in AQP4-NMOSD.
  • ADEM-like presentations – encephalopathy, multifocal deficits, seizures (especially in children).
  • Cortical/brainstem encephalitis – focal seizures, cortical deficits, or brainstem sym