Anti-Glycolipid Antibody and Anti-MAG Antibody Testing
Anti-glycolipid antibodies are found in a significant proportion of patients with a variety of autoimmune peripheral neuropathies. They are measured in the serum by enzyme-linked immunosorbent assay (ELISA). A wide variety of anti-glycolipid antibodies are present under different clinical circumstances and the laboratory offers a range of diagnostic tests using a panel of up to 12 glycolipid antigens. Such investigations can be useful to classify acute and chronic motor or sensory neuropathies and thus aide diagnosis and clinical management. Anti-glycolipid antibodies are associated with several distinct peripheral nerves syndromes: Multifocal motor neuropathy is associated with anti-GM1, -GA1 and -GD1b IgM antibodies. Chronic ataxic neuropathy with ophthalmoplegia M-protein, cold agglutination, and disialosyl antibodies (acronym: CANOMAD) is associated with anti-GD1b and related IgM antibodies. Miller Fisher syndrome is associated with anti-GQ1b and -GT1a IgG antibodies. Acute motor axonal neuropathy (AMAN) is associated with anti-GM1 and -GD1a IgG antibodies. A clinically important form of IgM paraproteinaemic neuropathy is associated with antibodies to myelin-associated glycoprotein (MAG) and a closely related glycolipid termed sulphated glucuronyl paragloboside. These antibodies are detected by a commercial ELISA assay kit using MAG as the antigen. The neuropathy has a characteristic clinic pattern and in the vast majority of cases is associated with an IgM gammopathy. Around 50% of patients with neuropathy-associated IgM gammopathy have anti-MAG antibodies. ELISAs depend on the fact that antibodies or antigen can be linked to an enzyme, with the complex retaining both immunological and enzymatic activity. In these assays the antigen (ganglioside) is attached to a solid phase support (ELISA plate) to allow for easy separation of bound and free antibody (patient serum). Detection is by a horseradish peroxidase labelled anti-human serum which can be visualized by a colour reagent and read spectrophotometrically. 1ml of serum is required for these investigations. The assay is conducted every week and results are despatched the following day.