X-linked myotubular myopathy

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X-linked myotubular myopathy
Synonyms	Myotubular myopathy, MTM1
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Specialty	Neurology, Genetics
Symptoms	Muscle weakness, hypotonia, respiratory difficulties
Complications	N/A
Onset	Infancy
Duration	Lifelong
Types	N/A
Causes	Mutations in the MTM1 gene
Risks	Male gender (due to X-linked inheritance)
Diagnosis	Genetic testing, Muscle biopsy
Differential diagnosis	Congenital myopathy, Spinal muscular atrophy
Prevention	N/A
Treatment	Supportive care, Physical therapy, Respiratory support
Medication	N/A
Prognosis	Variable, often severe
Frequency	Rare
Deaths

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

X-linked centronuclear myopathy; XLCNM; XLMTM

Cause

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

Signs and symptoms

30%-79% of people have these symptoms

• Areflexia
• Atrioventricular block
• Cavernous hemangioma
• External ophthalmoplegia
• Gait disturbance
• Head tremor
• Mask-like facies
• Muscular hypotonia
• Ptosis
• Scoliosis
• Seizure
• Skeletal muscle atrophy
• Muscle degeneration

Less common symptoms

• 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

X-linked recessive inheritance

Diagnosis

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

Genetic testing

• 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

• 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

• 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‚Äôs) side of each generation.

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