Table 1: Three types of striational antibodies in myasthenia gravis (MG).

AutoantigenTitinRyanodine receptorVoltage-gated K channel (VGKC)

Molecular structureSkeletal and cardiac sarcomereRyR1: skeletal typeBrain, nerve, skeletal, and heart muscles
Giant protein (3000 kD)RyR2: cardiac typeHomo- or hetero-tetramers
Repetitive structure565 kD with 4 homologous subunitsOne α-subunit (73 kD)

Original reportAarli et al. 1990 [7]Mygland et al. 1992 [11]Suzuki et al. 2005 [13]

Antibodies detectionELISA (commercially available)ELISA, Western blotImmunoprecipitation assay
Myasthenia gravis titin-30 (MGT-30) near the A/I-band junctionEpitopes in both RyR1 and RyR235-S-labeled rabdomyosarcoma cell
Sarcoplasmic reticulum from rabbit skeletal muscle N- and C-terminus of RyR1 sequenceBand at 70 kD

Epidemiology 20–40% in all MG patients13–38% in all MG patients12–15% in all MG patients
60–80% in MG patients older than 60 yearsMean onset age: 57 yearsMean onset age: 49 years
32% in nonthymoma MG patients older than 50 yearsM : F = 1 : 1M : F = 1 : 1

ImmunopathogenesisT cell proliferative response to MGT-30Complement activationDifferent from neuronal VGKC
Complement activationInhibiting Ca2+ release from sarcoplasmic reticulumQT prolongation on electrocardiogram
Myopathy in electromyogramAutoantibodies to dihydropyridine receptor
Association with DR7 in Caucasiansor transient receptor potential canonical type-3
Inhibiting excitation-contraction coupling

Thymoma-associated MG (T-MG) 49–95% in T-MG70–80% in T-MG40–70% in T-MG
Titin epitope expressionRyR epitope expressionKv1.4 mRNA expression
Production from clonal thymic B cellsDiagnosis of thymoma
Diagnosis of thymoma (younger than 50 years)C-terminal regions in RyR1 as epitope 

Clinical presentationAssociation with severe MGMore severe than anti-titinMore severe with anti-titin
Concomitant with myositisBulbar, respiratory, and neck involvementBulbar involvement and myasthenic crisisMyocarditis and/or myositis
Myocarditis and/or myositisLethal arrhythmias

Treatment and managementSome late-onset MG with ocular typeEarly pharmacological effect of tacrolimusResponder to calcineurin inhibitors
 poor prognosis in invasive thymomaSudden death