What causes myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

MG is idiopathic in most patients. Although the main cause behind its development remains speculative, the end result is a derangement of immune system regulation. MG is clearly an autoimmune disease in which the specific antibody has been characterized completely. In as many as 90% of generalized cases, IgG to AChR is present. [14] Even in patients who do not develop clinical myasthenia, anti-AChR antibodies can sometimes be demonstrated.

Patients who are negative for anti-AChR antibodies may be seropositive for antibodies against MuSK. Muscle biopsies of these patients show myopathic features with prominent mitochondrial abnormalities, as opposed to the neurogenic features and atrophy frequently found in MG patients positive for anti-AChR. The mitochondrial impairment could explain the oculobulbar involvement in anti-MuSK–positive MG. [24]

Numerous findings have been associated with MG. For example, people with certain human leukocyte antigen (HLA) types have a genetic predisposition to autoimmune diseases. The histocompatibility complex profile includes HLA-A1, -A3, -B7, -B8, -DRw3, and -DQw2 (though these have not been shown to be associated with the strictly ocular form of MG). However, HLA genotyping is not routinely used in the evaluation of patients suspected to have MG.

Sensitization to a foreign antigen that has cross-reactivity with the nicotinic ACh receptor has been proposed as a cause of myasthenia gravis, but the triggering antigen has not yet been identified.


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