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June 2001

Titin, Thymoma, and Myasthenia Gravis

Arch Neurol. 2001;58(6):869-870. doi:10.1001/archneur.58.6.869

TITIN WAS FIRST described in 1977 and given the name connectin.1 This giant, filamentous protein found in striated muscle was not demonstrated earlier because its size made it inaccessible to most techniques employed for protein identification. Titin is the largest molecule so far identified in the human body and has a molecular weight of about 3000 kd. Although abundant, it constitutes only approximately 10% of the total protein mass of striated muscle. Each titin molecule spans a half sarcomere, from the Z disk to the M line.2 The titin filaments contribute to muscle assembly and to the ability of muscle to spring back after it is stretched. Length changes in titin during stretching and contraction occur mainly in the I band, while the A band is functionally stiff and highly ordered.