X-linked myotubular myopathy

X-linked myotubular myopathy (XLMTM) is a type of centronuclear myopathy, which is a group of rare, inherited conditions that affect the muscles. XLMTM, specifically, occurs almost exclusively in males and is characterized by progressive muscle weakness (myopathy) and decreased muscle tone (hypotonia) that can range from mild to severe. The muscle problems impair the development of motor skills such as sitting, standing, and walking, and may disrupt primary functions such as breathing and feeding. XLMTM is caused by changes (mutations) in the MTM1 gene and is inherited in an X-linked recessive manner. Treatment is based on the signs and symptoms present in each person and may include physical and/or occupational therapy and assistive devices to help with mobility, eating and/or breathing.

Other Names[edit | edit source]

X-linked centronuclear myopathy; XLCNM; XLMTM

Cause[edit | edit source]

This condition is caused by mutations in the myotubularin (MTM1) gene which is located on the long arm of the X chromosome (Xq28).

X-linked recessive

Signs and symptoms[edit | edit source]

30%-79% of people have these symptoms

Less common symptoms[edit | edit source]

Arachnodactyly
Cryptorchidism
Decreased fetal movement
Decreased liver function
Diaphragmatic eventration
Bell's palsy
Flexion contracture
Generalized muscle weakness
High palate
Hydrocephalus
Hypokinesia
Long face
Macrocephaly
Narrow face
Neck muscle weakness
Neonatal respiratory distress
Polyhydramnios
Pyloric stenosis
Respiratory failure
Severe muscular hypotonia
Slender toe

Inheritance[edit | edit source]

X-linked recessive inheritance

Diagnosis[edit | edit source]

Making a diagnosis for a genetic or rare disease can often be challenging.
Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis.

Genetic testing[edit | edit source]

The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition.
The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a healthcare provider or a genetics professional

Presentation[edit | edit source]

This condition is found almost always in male infants.
It is one of the severest congenital muscle diseases and is characterized by marked muscle weakness, hypotonia and feeding and breathing difficulties.

Genetics[edit | edit source]

Many clinicians and researchers use the abbreviations XL-MTM, XLMTM or X-MTM to emphasize that the genetic abnormality for myotubular myopathy (MTM) is X-linked (XL), having been identified as occurring on the X chromosome.
The specific gene on the X chromosome is referred to as MTM-1.
In theory, some cases of CNM may be caused by an abnormality on the X chromosome, but located at a different site from the gene MTM1, but currently MTM1 is the only X-linked genetic mutation site identified for myotubular or centronuclear myopathy.
Clinical suspicion for X-linked inheritance would be a disease affecting multiple boys (but no girls) and a pedigree chart showing inheritance only through the maternal (mother’s) side of each generation.

X-linked myotubular myopathy Resources
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