We predicted that thymoma-associated antibodies (titin-Ab, SMA-Ab, and CAE-Ab) and anti-M7 antibodies play an important role in the concurrent presence of MG and myositis and myocarditis.
AChR antibodies (17.0 nmol/L, RF < 0.4) and titin antibodies were positive and repetitive nerve stimulation showed an abnormal decrement matching the criteria of myasthenia gravis.
In this study, we evaluated the clinical characteristics, autoantibody status (antibodies against AChR, MuSK, LRP4, titin and RyR) and genetic susceptibility (CHRNA1, CTLA4 and AIRE) in 114 Chinese JMG patients, and compared with 207 young adult MG patients (onset age 18-40 years).
The phenotype of titin-MG depended on AChR-antibodies: AChR-antibody negative patients presented with mostly mild limb muscle weakness, whereas AChR-antibody positive patients showed more frequently severe symptoms, including myasthenic crisis, bulbar predominance, and thymoma.
Antibodies to titin were found in sera from 85.7% of MG patients with thymoma (all age groups) and in 58% of nonthymomatous MG with late onset and acetylcholine receptor antibodies.
Patients having MG, including those with thymoma, who have the titin antibody are most often homozygous for the TNFA*T1 and TNFB*2 alleles, whereas the presence of the TNFA*T2 and TNFB*1 alleles correlates with early-onset MG and the absence of titin antibodies.