Hereditary myopathy with early respiratory failure

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Hereditary myopathy with early respiratory failure (HMERF) is an inherited disease that affects muscles used for movement (skeletal muscles) and muscles that are needed for breathing (respiratory muscles).

The major signs and symptoms of HMERF usually appear in adulthood, often in the mid-thirties. Among the earliest signs of the condition are breathing problems and difficulty walking. Weakness of the respiratory muscles, particularly the diaphragm (the muscle that separates the organs in the abdomen from those in the chest), causes breathing problems. This weakness worsens over time and can lead to life-threatening respiratory failure. Some affected individuals have weakness of muscles of the lower leg and foot, which makes it difficult to lift the toes while walking, a condition known as foot drop. Other muscles that become weak in people with HMERF include those of the hips, thighs, upper arms, and neck.

When viewed under a microscope, muscle fibers from affected individuals contain abnormal structures called cytoplasmic bodies. In many cases, the cytoplasmic bodies are arranged side-by-side in a ring inside the muscle fiber, resembling a necklace (necklace cytoplasmic bodies).

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

HMERF is caused by mutations in the TTN gene. This gene provides instructions for making a protein called titin. Titin plays an important role in muscles the body uses for movement (skeletal muscles) and in heart (cardiac) muscle.

Within muscle cells, titin is an essential component of structures called sarcomeres. Sarcomeres are the basic units of muscle contraction; they are made of proteins that generate the mechanical force needed for muscles to contract. Titin has several functions within sarcomeres. One of its most important jobs is to act as a backbone in these structures, providing structure, flexibility, and stability. Titin also plays a role in chemical signaling and in assembling new sarcomeres.

The TTN gene mutations responsible for HMERF lead to the production of an altered version of the titin protein that cannot fold into its normal 3-dimensional shape. Researchers are studying how abnormally folded titin contributes to the muscle damage that underlies the signs and symptoms of HMERF. It is unclear why these effects are usually limited to skeletal muscles and respiratory muscles, and do not involve cardiac muscle.

Rarely, people with the characteristic features of HMERF do not have identified mutations in the TTN gene. In these cases, the genetic cause of the condition is unknown.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

HMERF is typically inherited in an autosomal dominant pattern, which means one copy of the altered TTN gene in each cell is sufficient to cause the disorder. An affected person usually has one parent with the condition.

In rare cases, a specific mutation in one copy of the TTN gene leads to mild signs and symptoms of the condition, such as respiratory problems that begin later than is typical in HMERF with no other muscle weakness. However, family members who have the mutation in both copies of the gene have severe features of HMERF.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

HMERF is a rare condition with an unknown prevalence. It has been found in populations worldwide.

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.

Dyspnea · Frequent (79-30%)

Difficult or labored breathing. Dyspnea is a subjective feeling only the patient can rate, e.g., on a Borg scale.

EMG: myopathic abnormalities · Frequent (79-30%)

The presence of abnormal electromyographic patterns indicative of myopathy, such as small-short polyphasic motor unit potentials.

Elevated circulating creatine kinase concentration · Frequent (79-30%)

The activity of creatine kinase in the blood circulation is above the upper limit of normal.

Foot dorsiflexor weakness · Frequent (79-30%)

Weakness of the muscles responsible for dorsiflexion of the foot, that is, of the movement of the toes towards the shin. The foot dorsiflexors include the tibialis anterior, the extensor hallucis longus, the extensor digitorum longus, and the peroneus tertius muscles.

Gait disturbance · Frequent (79-30%)

The term gait disturbance can refer to any disruption of the ability to walk.

Increased variability in muscle fiber diameter · Frequent (79-30%)

An abnormally high degree of muscle fiber size variation. This phenotypic feature can be observed upon muscle biopsy.

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

An abnormally increased proportion of nuclei of sarcomeres with an internal localization. Individual muscle fibers are syncytia, formed by embryonic fusion of many myoblasts or later, myosatellite cells. Each muscle fiber contains many nuclei, peripherally positioned immediately adjacent to the sarcolemmal membrane. In healthy muscle only 3-5% of fibers contain nuclei that are located internally, within the cell, but many disease processes lead to internal nuclei.

Limited hip movement · Frequent (79-30%)

A decreased ability to move the femur at the hip joint associated with a decreased range of motion of the hip.

Other findings in the same source

From: Orphanet

Additional reported features include Muscle fiber splitting (Frequent (79-30%)); Neck flexor weakness (Frequent (79-30%)); Orthopnea (Frequent (79-30%)); Reduced vital capacity (Frequent (79-30%)); Restrictive ventilatory defect (Frequent (79-30%)); Rimmed vacuoles (Frequent (79-30%)); Skeletal muscle atrophy (Frequent (79-30%)); Type 1 muscle fiber predominance (Frequent (79-30%)); Necrotizing myopathy (Frequent (79-30%)); Respiratory insufficiency due to muscle weakness (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Hereditary myopathy with early respiratory failure 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 Hereditary myopathy with early respiratory failure. 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.