Congenital Tubular Aggregate Myopathy

Abstract

This form of congenital myopathy is characterized by slowly progressive weakness without atrophy, myalgia, cramps, or episodic weakness and by muscle biopsy showing 60–90% of fibers containing tubular aggregates. Tubular aggregates are microscopic structures of variable appearance consisting of an outer tubule containing either one or more microtubule-like structures or amorphous material. They are a nonspecific pathologic finding that may occur in a variety of circumstances, including alcohol- and drug-induced myopathies, exercise-induced cramps or muscle weakness, and inherited myopathies. Tubular aggregates derive from the sarcoplasmic reticulum and are believed to represent an adaptive mechanism to regulate an increased intracellular level of calcium and prevent hypercontraction and necrosis of muscle fibers. Indeed, an excess of calcium could promote a sarcoplasmic reticulum remodeling. Autosomal dominant tubular aggregate myopathy was recognized to be caused by mutations in the STIM1 gene, encoding calcium sensor STIM1 (Table 49.1).