The measurement of antibodies against gangliosides is used in the investigation of certain neurological diseases, mainly motor neuropathies.
Peripheral neuropathies are a group of disorders resulting from damage to the peripheral nerves. Patients with peripheral neuropathy can develop symptoms of weakness, unconsciousness, and / or dysfunction of the autonomic nervous system. The causes of acquired peripheral neuropathies vary and include vitamin deficiency, metabolic abnormalities, infections, malignancies (paraneoplastic syndromes) and autoimmune diseases. A percentage of peripheral neuropathies are autoimmune in etiology and are associated with the presence of autoantibodies against specific gangliosides.
Gangliosides are glycosphingolipids present in the lipid bilayer of cell membranes. They consist of a hydrophobic membrane portion (ceramide) and one or more sugars and sialic acids that form the extracellular portion.
About twenty different gangliosides have been described. Their name always starts with G (from Ganglioside), the second letter indicates the number of sialic acids (Mono, Di, Tri, Quad, for 1, 2, 3 or 4 sialic acids respectively) and the number is occasionally followed by a lowercase letter which represents the position of the ganglioside in thin layer chromatography.
Therefore, GM1 consists of one sialic acid and 4 sugars, GQ1b of 4 sialic acids and 4 sugars. Gangliosides are involved in many functions: growth and cell differentiation, apoptosis, adhesion, regulation of the immune system, etc. They are also receptors for a wide range of germs, viruses and toxins.
Although present in the plasma membranes of many cell types, gangliosides are particularly abundant in neural tissue. GM1, GD1a, GD1b and GT1b are found in large quantities in the peripheral nerves. GQ1b is found only in the optic nerve.
Although the involvement of antibodies against gangliosides in the pathophysiological mechanism of the disease is questionable, their identification in various peripheral neuropathies provides important diagnostic assistance.
- In conductive block motor neuropathies: Antibodies against GM1 and GD1b IgM are present in approximately 75% of cases.
- In motor neuropathies without conduction block especially in amyotrophic lateral sclerosis (ALS).
- In chronic peripheral neuropathies: the presence of monoclonal IgM antibodies against GM1, GM2, GD1a, GD1b or GT1b determines 5 separate clinical entities.
- In axial forms of Guillain-Barré syndrome: After infection with Campylobacter jejunii, IgG antibodies against GM1 or GD1b are found in 95% of cases in the acute phase and then disappear within 6 months if the disease is cured. In contrast, in the "classic" Guillain-Barré syndrome, antibodies against GM1 are present in 20 to 30% of cases and their titers are of limited importance.
- In Miller-Fischer Syndrome (Ophthalmoplegia Associated with Polymeric Neuritis): High IgG antibodies against GQ1b are found in 90% of cases.
Antibodies against gangliosides tested in Diagnostiki Athinon are as follows:
- Anti-GM1 IgG & IgM & Total
- Anti-GM2 IgG & IgM & Total
- Anti-GM3 IgG & IgM & Total
- Anti-GM4 IgG & IgM & Total
- Anti-GD1a IgG & IgM & Total
- Anti-GD1b IgG & IgM & Total
- Anti-GD2 IgG & IgM & Total
- Anti-GD3 IgG & IgM & Total
- Anti-GT1a IgG & IgM & Overall
- Anti-GT1b IgG & IgM & Total
- Anti-GQ1b IgG & IgM & Total