Central core disease

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Central core disease is a disorder that affects muscles used for movement (skeletal muscles). This condition causes muscle weakness that ranges from barely noticeable to very severe. The severity of muscle weakness may differ even among affected members of the same family.

Most people with central core disease experience persistent, mild muscle weakness that does not worsen with time. This weakness affects the muscles near the center of the body (proximal muscles), particularly muscles in the shoulders, upper legs, and hips. Muscle weakness in affected infants can delay the development of motor skills such as sitting, standing, and walking; most people with this condition are able to walk independently. Affected individuals may experience muscle pain (myalgia) or extreme fatigue in response to physical activity (exercise intolerance). Central core disease is also associated with eyes that do not look in the same direction (strabismus), a rounded upper back that also curves to the side (kyphoscoliosis), foot deformities, hip dislocation, and joint deformities called contractures that restrict the movement of certain joints. In severe cases, affected infants experience weakness in the muscles of the face, profound low muscle tone (hypotonia), and serious or life-threatening breathing problems.

Many people with central core disease also have an increased risk of developing a severe reaction to certain drugs used during surgery and other invasive procedures. This reaction is called malignant hyperthermia. Malignant hyperthermia occurs in response to some anesthetic gases, which are used to block the sensation of pain, either given alone or in combination with a muscle relaxant that is used to temporarily paralyze a person during a surgical procedure. If given these drugs, people at risk of malignant hyperthermia may experience a rapid increase in heart rate (tachycardia) and body temperature (hyperthermia), abnormally fast breathing (tachypnea), muscle rigidity, breakdown of muscle fibers (rhabdomyolysis), and increased acid levels in the blood and other tissues (acidosis). The complications of malignant hyperthermia can be life-threatening unless they are treated promptly.

Central core disease gets its name from disorganized areas called central cores, which are typically found in the center of skeletal muscle cells, but can be at the edges or span the length of the cell, in many affected individuals. These abnormal regions can only been seen when muscle tissue is viewed under a microscope. These central cores are often present in cells with few or no mitochondria, which produce energy within cells. Although the presence of central cores can help doctors diagnose central core disease, it is unclear how they are related to muscle weakness and the other features of this condition.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the RYR1 gene cause central core disease. The RYR1 gene provides instructions for making a protein called ryanodine receptor 1. This protein plays an essential role in skeletal muscles. For the body to move normally, these muscles must tense (contract) and relax in a coordinated way. Muscle contractions are triggered by the flow of charged atoms (ions) into muscle cells. The ryanodine receptor 1 protein forms a channel that releases calcium ions stored within muscle cells. The resulting increase in calcium ion concentration inside muscle cells stimulates muscle fibers to contract, allowing the body to move.

Mutations in the RYR1 gene change the structure of ryanodine receptor 1 and the calcium channel that it forms. The abnormal calcium channel alters the normal flow of stored calcium ions within muscle cells. Specifically, calcium ions "leak" slowly but continually through the abnormal channel or calcium ions cannot pass through the channel when they are needed. This disruption in calcium ion transport prevents muscles from contracting normally, leading to the muscle weakness characteristic of central core disease.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Central core disease is most often inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases may result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.

Less commonly, central core disease is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but typically do not show signs and symptoms of the condition. People who carry one RYR1 gene mutation, however, may be at increased risk for malignant hyperthermia.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

The exact prevalence of central core disease is unknown. However, it is thought to be the most common of the congenital myopathies, which are a group of muscle disorders that cause weakness very early in life. As a group, congenital myopathies affect 6 per 100,00 newborns.

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.

Central core regions in muscle fibers · Frequent (79-30%)

The presence of disorganized areas called cores in the center of muscle fibers. There is a typical appearance of the biopsy on light microscopy, where the muscle cells have cores that are devoid of mitochondria and specific enzymes. Cores are typically well demarcated and centrally located, but may occasionally be multiple and of eccentric.

Easy fatigability · Frequent (79-30%)

Increased susceptibility to fatigue.

Hypotonia · Frequent (79-30%)

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Joint hypermobility · Frequent (79-30%)

The capability that a joint (or a group of joints) has to move, passively and/or actively, beyond normal limits along physiological axes.

Kyphoscoliosis · Frequent (79-30%)

An abnormal curvature of the spine in both a coronal (lateral) and sagittal (back-to-front) plane.

Malignant hyperthermia · Frequent (79-30%)

Malignant hyperthermia is characterized by a rapid increase in temperature to 39-42 degrees C. Malignant hyperthermia may occur in response to either inhalational anesthetics such as halothane, to muscle relaxants such as succinylcholine, or to exercise.

Mitral valve prolapse · Frequent (79-30%)

One or both of the leaflets (cusps) of the mitral valve bulges back into the left atrium upon contraction of the left ventricle.

Motor delay · Frequent (79-30%)

A type of Developmental delay characterized by a delay in acquiring motor skills.

Other findings in the same source

From: Orphanet

Additional reported features include Muscle stiffness (Frequent (79-30%)); Myopathy (Frequent (79-30%)); Pelvic girdle muscle weakness (Frequent (79-30%)); Pes planus (Frequent (79-30%)); Talipes equinovarus (Frequent (79-30%)); Type 1 muscle fiber predominance (Frequent (79-30%)); Congenital hip dislocation (Frequent (79-30%)); Multiple joint contractures (Frequent (79-30%)); Abnormal circulating creatine kinase concentration (Occasional (29-5%)); Nemaline bodies (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Central core disease 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

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

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.