Antibodies against the calcium channel β‐subunit in Lambert‐Eaton myasthenic syndrome

The sera of patients with Lambert-Eaton myasthenic syndrome (LEMS) contain autoantibodies against several extracellular and intracellular components of the voltage-gated calcium channel (VGCC)/synaptic vesicle release complex. An example of the latter are anti-β-subunit antibodies (anti-MysB antibodies). We constructed a full-length cDNA clone of a human VGCC β-subunit to produce purified β-subunit fusion protein (MysB protein). Using this protein, we demonstrated that anti-β-subunit antibodies are present in the sera of 23% of LEMS patients and only, in low titer, in 2% of small cell lung cancer patients without LEMS. The presence of anti-β-subunit antibodies was closely associated with high titers of P/Q- and N-type VGCC antibodies. Immunization of rats with the purified MysB protein induced high antibody titers, but no signs of neurologic dysfunction were found. We conclude that anti-β-subunit antibodies are not likely to interfere with ion channel function, but their presence could explain the cross-reactivity of LEMS sera with several subtypes of VGCCs and the lack of correlation between anti-VGCC antibody titer and clinical severity of disease.