Skeletal muscle titin: physiology and pathophysiology

Titins are a family of gigantic filamentous muscle proteins essential for m uscle structure, function and development. Most of their sequence consists of repetitive modules of two superfamily motifs, immunoglobulin and fibrone ctin, interspersed with unique sequences. A special feature is that many re gions are differentially expressed in different muscle types, providing uni que characteristics. Titin is evolutionarily old, and many regions are high ly conserved. Most mutations that alter titin's characteristics seem to be incompatible with life, since very few associated genetic diseases have bee n described. The autoimmune response against titin in the paraneoplastic fo rm of myasthenia gravis is discussed.