Myofibrillar myopathy

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Myofibrillar myopathy refers to a group of disorders that are characterized by muscle weakness (myopathy) that worsens over time. Myofibrillar myopathy primarily affects the skeletal muscles, which are the muscles that the body uses for movement. In some cases, the heart (cardiac) muscle is also affected.

The signs and symptoms of myofibrillar myopathy vary widely among affected individuals. People with this disorder typically begin to develop myopathy in mid-adulthood. However, the features of this condition can appear anytime between infancy and late adulthood. Myopathy most often begins in the hands, forearms, feet, and lower legs (distal muscles), but some people first experience weakness in the muscles near the center of the body (proximal muscles). The weakness can spread to other muscles.

Other signs and symptoms of myofibrillar myopathy can include muscle pain (myalgia) or weakness and loss of sensation in the limbs (peripheral neuropathy). Affected individuals may also have skeletal problems, which can include joint stiffness (contractures) and abnormal side-to-side curvature of the spine (scoliosis). Some people with myofibrillar myopathy develop clouding in the lenses of the eyes (cataracts).

Some people with myofibrillar myopathy develop cardiomyopathy, which is a weakening of the heart muscle. In some cases, cardiomyopathy is the first sign of the disorder.

In rare cases, the muscles used for speaking, swallowing, or breathing are affected in people with myofibrillar myopathy. When the muscles used for breathing are involved, affected individuals may experience extreme tiredness (fatigue), breathing difficulties, and, in severe cases, respiratory failure.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also called mutations) in several genes can cause myofibrillar myopathy. These genes provide instructions for making proteins that play an important role in muscle contraction. Within muscle fibers, structures called sarcomeres generate the force needed for muscles to contract. Structures called Z-discs link neighboring sarcomeres together to form myofibrils, which are the basic units of muscle fibers. The organization of sarcomeres and myofibrils provides the strength and stability that is needed during repeated cycles of muscle contraction and relaxation. Many of the genes that are associated with myofibrillar myopathy provide instructions for making proteins that are involved in the function of Z-discs.

Variants in the DES, MYOT, and LDB3 genes are among the main causes of myofibrillar myopathy. Variants in these genes cause cells to produce proteins that do not function properly. Because these abnormal proteins do not interact with Z discs as they should, the coordinated arrangement of sarcomeres and myofibrils is disrupted. Myofibrils that are not formed correctly break down and form clumps (aggregates) of abnormal proteins within the sarcomere, which leads to the myopathy seen in people with myofibrillar myopathy.

Approximately 30 to 50 percent of affected individuals do not have variants in the genes known to be associated with myofibrillar myopathy. In these cases, the cause of the condition is unknown.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Myofibrillar myopathy has different inheritance patterns depending on which gene is involved.

The condition is typically inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Some cases of myofibrillar myopathy result from new (de novo) variants in the gene that occur during the formation of reproductive cells (eggs or sperm) in an affected individual's parent or during early embryonic development.

In rare cases, myofibrillar myopathy is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Although myofibrillar myopathy is considered a rare disorder, the exact number of people who have the condition is unknown.

Which doctor should you see?

The suggested department for discussing Myofibrillar myopathy is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

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.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Myofibrillar 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.