Author Affiliations: Department of Neurology, University of California, Davis.
Myasthenia gravis (MG) is a disorder of the neuromuscular junction (NMJ) characterized by muscle weakness that worsens with effort and improves with rest. The electrodiagnostic correlate is decrementing compound muscle action potential amplitudes to slow rates of repetitive nerve stimulation. Although rare forms of myasthenia result from heritable mutations in individual proteins comprising the NMJ, the congenital myasthenic syndromes,1 the vast majority of cases of MG are autoimmune in origin. For 90% of patients with generalized autoimmune MG (ie, involving more than the ocular muscles), the disorder results from circulating autoantibodies to the nicotinic acetylcholine receptor (AChR), which is the NMJ postsynaptic neurotransmitter receptor. The remaining 10% of patients have been referred to as having seronegative (autoimmune) MG. About a decade ago, Hoch and coworkers2 identified antibodies to a second postsynaptic NMJ membrane protein, muscle-specific kinase (MuSK) present in about 40% of seronegative patients. Subsequent studies3- 6 in rodents have provided data supporting a pathogenic role for MuSK antibodies in this subgroup of patients. It is the remaining 60% of seronegative patients (now referred to as patients with double-seronegative MG) who are the subject of the study of antibodies to low density lipoprotein receptor-related protein 4 (LRP4) by Zhang et al7 published in this issue of the Archives.
Richman DP. Antibodies to Low Density Lipoprotein Receptor-Related Protein 4 in Seronegative Myasthenia Gravis. Arch Neurol. 2012;69(4):434-435. doi:10.1001/archneurol.2011.2855