X-linked myotubular myopathy

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

X-linked myotubular myopathy is a condition that primarily affects muscles used for movement (skeletal muscles) and occurs almost exclusively in males. People with this condition have muscle weakness (myopathy) and decreased muscle tone (hypotonia) that are usually evident at birth. When viewed under a microscope, the muscle fibers of affected individuals are typically small and underdeveloped.

The muscle problems in X-linked myotubular myopathy impair the development of motor skills such as sitting, standing, and walking. Affected infants may also have difficulties with feeding due to muscle weakness. Individuals with this condition often do not have the muscle strength to breathe regularly on their own and must be supported with a machine to help them get enough oxygen (mechanical ventilation). Some affected individuals need breathing assistance only periodically, typically during sleep, while others require it continuously. People with X-linked myotubular myopathy may also have weakness in the muscles that control eye movement (ophthalmoplegia), weakness in other muscles of the face, and absent reflexes (areflexia).

In X-linked myotubular myopathy, muscle weakness often disrupts normal bone development and can lead to fragile bones, an abnormal curvature of the spine (scoliosis), and joint deformities (contractures) of the hips and knees. People with X-linked myotubular myopathy may have a large head with a narrow and elongated face and a high, arched roof of the mouth (palate). They may also have recurrent ear and respiratory infections, seizures, or liver disease. Some affected individuals develop a serious liver condition called peliosis hepatitis, which can cause life-threatening bleeding (hemorrhage).

Because of their severe breathing problems, individuals with X-linked myotubular myopathy usually survive only into early childhood; however, some people with this condition have lived into adulthood.

X-linked myotubular myopathy is the most severe condition in a group of disorders called centronuclear myopathy. In centronuclear myopathy, the nucleus is found at the center of many rod-shaped muscle cells instead of at either end, where it is normally located.

ORPHANET DEFINITION A rare X-linked congenital myopathy characterized by numerous centrally placed nuclei on muscle biopsy and that presents at birth with marked weakness, hypotonia and respiratory failure.

Inheritance

From: MedlinePlus Genetics, National Library of Medicine

X-linked recessive

Frequency in the source

From: MedlinePlus Genetics, National Library of Medicine

Prevalence at birth: 1-9 / 100 000; France; Value and class. Point prevalence: 1-9 / 1 000 000; Europe; Value and class.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Type 1 fibers relatively smaller than type 2 fibers · Very frequent (99-80%)

The presence of abnormal muscle fiber size such that type 1 fibers are smaller than type 2 fibers.

Low APGAR score · Very frequent (99-80%)

Abnormality of the eye · Frequent (79-30%)

Any abnormality of the eye, including location, spacing, and intraocular abnormalities.

Centrally nucleated skeletal muscle fibers · Frequent (79-30%)

An abnormality in which the nuclei of sarcomeres take on an abnormally central localization (or in which this feature is found in an increased proportion of muscle cells).

Decreased fetal movement · Frequent (79-30%)

An abnormal reduction in quantity or strength of fetal movements.

Fatigable weakness of bulbar muscles · Frequent (79-30%)

A type of weakness of the bulbar muscles (muscles of the mouth and throat responsible for speech and swallowing) that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions.

Fatigable weakness of swallowing muscles · Frequent (79-30%)

A type of weakness of the muscles involved in swallowing that occurs after a muscle group is used and lessens if the muscle group has some rest. That is, there is diminution of strength with repetitive muscle actions.

Feeding difficulties in infancy · Frequent (79-30%)

Impaired feeding performance of an infant as manifested by difficulties such as weak and ineffective sucking, brief bursts of sucking, and falling asleep during sucking. There may be difficulties with chewing or maintaining attention.

Necklace skeletal muscle fibers · Frequent (79-30%)

A histological alteration of muscle fibers that resembles a necklace (necklace fibers). A substantial proportion of fibers (4-20% in PMID:19084976) show internalized nuclei aligned in a basophilic ring (necklace) at 3 micrometers beneath the sarcolemma. Ultrastructurally, such necklaces consist of myofibrils of smaller diameter, in oblique orientation, surrounded by mitochondria, sarcoplasmic reticulum and glycogen granules.

Neonatal hypotonia · Frequent (79-30%)

Muscular hypotonia (abnormally low muscle tone) manifesting in the neonatal period.

Pneumonia · Frequent (79-30%)

Inflammation of any part of the lung parenchyma.

Polyhydramnios · Frequent (79-30%)

The presence of excess amniotic fluid in the uterus during pregnancy.

Poor suck · Frequent (79-30%)

An inadequate sucking reflex, resulting in the difficult of newborns to be breast-fed.

Premature birth · Frequent (79-30%)

The birth of a baby of less than 37 weeks of gestational age.

Other findings in the same source

From: Orphanet

Additional reported features include Recurrent respiratory infections (Frequent (79-30%)); Respiratory distress (Frequent (79-30%)); Respiratory failure requiring assisted ventilation (Frequent (79-30%)); Severe muscular hypotonia (Frequent (79-30%)); Weakness of facial musculature (Frequent (79-30%)); Abnormal facial shape (Occasional (29-5%)); Dolichocephaly (Occasional (29-5%)); High palate (Occasional (29-5%)); Inability to walk (Occasional (29-5%)); Long face (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: MedlinePlus Genetics, National Library of Medicine

Antenatal; Neonatal

Inheritance in the source

From: MedlinePlus Genetics, National Library of Medicine

X-linked recessive

Frequency and the population described

From: MedlinePlus Genetics, National Library of Medicine

Prevalence at birth: 1-9 / 100 000; France; Value and class. Point prevalence: 1-9 / 1 000 000; Europe; Value and class.

Understanding the inheritance label

From: MedlinePlus Genetics

An X-linked recessive pattern involves a gene on the X chromosome. The number of X chromosomes and the particular genetic change influence how a condition is expressed. A genetic counsellor should interpret the result and the family history before discussing risks for relatives or future pregnancies.

Which doctor should you see?

The suggested department for discussing X-linked myotubular myopathy is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for X-linked myotubular myopathy. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.