Cause - multiple origins; commonly caused by defects in a gene that carries instructions for a molecular "gate" that releases calcium from inside muscle cells

Onset - congenital; at or near birth

Symptoms - poor muscle tone (hypotonia) and persistent muscle weakness in infants; usually motor milestones reached late; skeletal deformities, including joint dislocations and scoliosis, often occur; susceptibility to malignant hyperthermia, a dangerous adverse reaction to anesthesia

Progression - slow or no progression

Inheritance - autosomal dominant, or produced by a defective gene contributed by one parent; possibly autosomal recessive, or produced by defective genes contributed by both parents, in rare cases

Facts About Myopathies