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X-Linked Myotubular Myopathy

Abstract

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NORD is very grateful to James J. Dowling, MD, PhD, Assistant Professor, Eisenberg Emerging Taubman Scholar, Departments of Pediatrics, Neurology, and Neuroscience, Director, Pediatric Neuromuscular Program, University of Michigan Medical Center, for assistance in the preparation of this report.

Synonyms of X-Linked Myotubular Myopathy

  • MTM
  • myotubular myopathy
  • XLCNM
  • x-linked centronuclear myopathy
  • XLMTM

Disorder Subdivisions

  • No subdivisions found.

General Discussion

Summary
X-linked myotubular myopathy (XLMTM) is a rare genetic neuromuscular disorder that is characterized by muscle weakness that can range from mild to profound. Symptoms are often present at birth, but may first develop during infancy or early childhood. In rare cases, symptoms may not develop until later, even adulthood. Common symptoms include mild to profound muscle weakness, diminished muscle tone (hypotonia or "floppiness"), feeding difficulties, and potentially severe breathing complications (respiratory distress). Feeding difficulties and respiratory distress develop because of weakness of the muscles that are involved in swallowing and breathing. The overall severity of the disorder can range from mildly affected individuals to individuals who develop severe, life-threatening complications during infancy and early childhood. Most affected individuals have a severe form of the disorder and respiratory failure is an almost uniform occurrence. XLMTM is caused by mutations to the myotubularin (MTM1) gene. The disorder is inherited as an X-linked recessive condition. The disorder predominantly affects males, but female carriers can develop mild symptoms. In rare specific cases, females can develop a severe form similar to that seen in males.

Introduction
XLMTM belongs to a larger group of disorders known as the centronuclear myopathies. In addition to XLMTM, there are forms of centronuclear myopathy that are inherited as autosomal dominant or autosomal recessive conditions. Generally, the autosomal forms are less severe than XLMTM, however, in rare cases, individuals with an autosomal form can develop severe complications that are similar to those seen in XLMTM. Centronuclear myopathies derive their name from the abnormal location of the nucleus in the center of the muscle fiber (muscle cell) rather than its normal position on the edge. Additional pathologic features include disorganized perinuclear organelles and abnormalities in oxidative staining patterns. Centronuclear myopathies can be further classified into the larger, broader category of congenital myopathy, a group of genetic muscle disorders that are present at birth.

In the medical literature, centronuclear myopathy is generally used for the autosomal forms of the disorder and myotubular myopathy is generally used for the X-linked form. Distinguishing between the X-linked (myotubular) form and the autosomal forms is essential as the symptoms are usually more severe in the X-linked form. NORD has a separate report on centronuclear myopathy that describes the autosomal forms in greater detail. This report specifically deals with X-linked centronuclear (myotubular) myopathy.

Organizations related to X-Linked Myotubular Myopathy

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