Probable cytoskeleton-associated protease required for normal muscle growth. Involved in function, maturation and stabilization of the neuromuscular junction. May act by cleaving muscle-specific proteins such as FLNC. Interacts with IGFN1 and FLNC. Specifically expressed in skeletal and cardiac muscle. Mice exhibit a primary degenerative myopathy preceding chronic thoraco-lumbar kyphoscoliosis. Used as a marker for 'occult' heart disease, as its absence does not cause heart pathology in heart. Belongs to the transglutaminase-like superfamily.