Craniofacial Muscles

78 F. Pedrosa Domellöf
Fig. 5.2 NMJs of human adult limb muscle do not bind antibodies against gangliosides GQ1b,
GT1a, and GD1b, in contrast to the extraocular muscles
cause of myasthenia gravis in approximately 85% of patients (Romi et al. 2005 ) .
Consequently, the fi nal step in signal transmission from the nerve to the muscle is
hampered and translates clinically into fatigable muscle weakness. However, these
autoantibodies are not always present in MG and false positives are found in other
autoimmune diseases, such as rheumatoid arthritis. Autoantibodies against other
muscle proteins such as muscle-speci fi c kinase (MuSK), titin, rapsyn, or ryanodine
may also be present in patients with myasthenia symptoms that are seronegative for
acetylcholine receptors (Romi et al. 2005 ) . Recently, matrix metalloproteinases 2,
3, and 9 have also been implicated in the pathogenesis of myasthenia gravis, independently
of the presence or absence of acetylcholine receptor antibodies (Helgeland
et al. 2011 ) . MG affects patients of all ages, with a peak in the second and third
decades for females and in the sixth and seventh decades for males, and it is associated
with thymus pathology in up to two-third of the patients and with thyroid
dysfunction in up to 10% of the cases.