Cause - the most common form (X-linked)caused by defects or deficiencies of myotubularin, a protein thought to promote normal muscle development

Onset - congenital (X-linked); infancy to early adulthood (autosomal recessive); childhood to adulthood (autosomal dominant)

Symptoms - X-linked: severe muscle weakness and hypotonia (lack of muscle tone) that interfere with posture and movement; life-threatening difficulties with feeding and respiration; possibility of anemia, gallstones and serious liver abnormalities; autosomal forms cause similar problems to X-linked, but autosomal dominant form considered mild; autosomal recessive form considered intermediate

Progression - affected children attain motor milestones slowly; in autosomal forms, muscle problems are progressive

Inheritance - X-linked, or carried on the X chromosome and usually affecting only boys; autosomal dominant, or produced by a defective gene contributed by one parent; also autosomal recessive, or produced by defective genes contributed by both parents

Facts About Myopathies