What Is Central Core Disease

Overview

Central core disease (CCD) is a rare genetic neuromuscular disorder which affects males and females equally. CCD is classified as a congenital myopathy, a condition that is present at birth and is characterised by muscle weakness and wasting. Although the exact incidence and prevalence of CCD are unknown, it is believed that CCD is the most common form of congenital myopathy.

CCD is characterised by the appearance of core-like structures running through the centres of muscle fibres. These cores were found to be metabolically inactive due to the lack of mitochondria (the crucial energy-producing structures). Symptoms vary widely in severity and can occur anytime from infancy to adulthood. Usually, people affected have a normal life span due to the disease progressing slowly or not at all.^1,2,3,4,5

Causes

CCD is a rare genetic neuromuscular disorder caused by a mutation in the ryanodine receptor (RYR1) gene, located on chromosome 19. RYR1 gene carries instructions for the production of ryanodine receptor calcium release channel involved in calcium regulation in skeletal (voluntary) muscle.

Mutations in RYR1 result in abnormalities in the normal flow of electrically charged calcium ions across cell membranes, which in turn results in the muscle’s inability to contract, and hence weakness and other symptoms associated with CCD.^1,2,3,4,5

In most cases, CCD is inherited in an autosomal dominant pattern, which means for the child to have the disease, it is enough to inherit the mutated gene from only one parent. If one of the parents has the condition, every child (whether female or male) has a 50% chance of having the condition as well. Nevertheless, in some cases, CCD can be inherited in an autosomal recessive pattern which is when an individual receives a mutated gene from both parents resulting in more severe symptoms.^1,2,3,4,5

Signs and symptoms

CCD symptoms and severity vary greatly from person to person. Some may develop very mild symptoms that may go unnoticed up until someone from the next generations (children or grandchildren) develops symptoms and undergoes genetic testing. Others may develop serious breathing (respiratory) or swallowing (gastrointestinal) difficulties, where assisted ventilation or a G-tube may be required.

General symptoms include:

• Hypotonia (floppiness)
• Muscle weakness at the trunk of the body.
• Motor delay (delayed walking, difficulty running or jumping)
• Muscle cramps
• Orthopaedic abnormalities such as spinal curvature (Scoliosis), foot deformities, hip/knee dislocation
• Certain facial muscles may be affected^1,2,3,4,5

Diagnosis

Generally, diagnosis involves a combination of patient and family history, a thorough clinical evaluation, detection of physical findings, and other diagnostic studies such as:

• Blood tests where normal or slightly elevated levels of creatine kinase (an enzyme released upon muscle breakdown) are detected
• Electromyography (EMG) is a test that records electrical activity in skeletal muscles when at rest and during muscle contraction. Certain muscle fibres during activity may be of unusually short duration and low amplitude
• Nerve conduction velocity assesses the motor and sensory nerve’s ability and speed to conduct nerve impulses
• Muscle biopsies These can be done in one of two ways:
  • A small piece of muscle is taken under general anaesthetic (avoiding drugs that may cause malignant hyperthermia)
  • A small sample is removed through a needle biopsy

These samples are then subjected to microscopic evaluation which reveals a distinctive pattern with dense core structures located at the centre of the muscle fibres (thread-like muscle cells within the skeletal muscle).

Nevertheless, core structures are also seen in other unrelated conditions, therefore, upon deciding on the diagnosis, it is important to consider the physical signs and symptoms as well as any molecular tests performed.

In families with known mutations in the RYR1 gene, molecular genetic testing can be done, where a blood sample is taken, and the DNA is analysed for the presence of a mutation. Although genetic testing can take up to several months to complete, it is gradually becoming the first step in the diagnostic process, with other evaluations performed to confirm the genetic results.^1,2,3,4,5

Treatment and management

Currently, there is no cure for CCD, but there are certain therapies targeting the specific symptoms apparent in each individual. These therapies may require the coordinated efforts of a team of medical professionals (paediatricians, orthopaedists, physiatrists, physical therapists, occupational therapists, and /or other health care professionals).^1,2,3,4,5

1.) Physiotherapy

The primary aim or the minimum objective of managing a muscle-wasting condition is to increase or at least maintain function and mobility.

Physiotherapy can help with that, as well as maintain breathing capacity, delay the onset of spinal curvature (scoliosis), and prevent the development of contractures. In case of “floppiness” during infancy, careful attention should be paid to posture, the use of adaptive seating with careful trunk and head support and other measures.^1,2,3,4,5

Make sure the physiotherapist is familiar with the treatment of people with muscle-wasting conditions.

2.) Exercise

Some clinicians say that strenuous exercise is not good for people with muscle-wasting conditions since putting additional strain on already weakened muscles can cause additional harm. Others believe that exercise may increase muscle strength. There is not enough evidence to support either of these theories, however, moderate non-weight-bearing exercise such as swimming, walking, or pedalling may be the best solution. These aerobic exercises maintain a healthy cardiovascular system and a steady weight. Should be properly discussed with a clinician.^1,2,3,4,5

3.) Corrective surgery

Scoliosis, which is the curvature of the spine, is common in CCD. Spinal surgery aims to correct the posture by re-aligning the spinal column and involves the insertion of rods, screws, or wires. There are benefits and risks associated with this surgery, therefore, it is important to discuss the options fully with a consultant or specialist before a decision is made. Young children might use a spinal brace, and those who do not walk may use moulded seating.^1,2,3,4,5

It is important to mention, that before any surgical procedure, great care must be taken about the type of anaesthetics and medications to be used. This is because when individuals with CCD are exposed to certain anaesthetic drugs, a serious adverse reaction, called Malignant hyperthermia, could develop.

Malignant hyperthermia is characterised by high body temperature, rigid muscles, spasms, rapid heart rate, high blood pressure, bluish skin colour (cyanosis), and other symptoms. If left untreated, the resulting complications can lead to death. The drugs that trigger malignant hyperthermia are:

• The volatile inhalation gases including sevoflurane, desflurane, isoflurane, halothane, enflurane, methoxyflurane
• Depolarizing muscle relaxants (such as succinylcholine)^1,2,3,4,5

4.) Genetic counselling

This is recommended for affected individuals and their families. It helps the individual to understand his/her condition better as well as understand what can be expected in the future and prepare oneself for the possibility of developing symptoms at any time in life.

Moreover, it helps to guide the individual to the best lifestyle to follow to slow the disease progression as much as possible. Furthermore, for those who are planning to have kids, it gives them a chance to avoid giving birth to an affected child.^1,2,3,4,5

FAQ's

What is the life expectancy of someone with CCD?

People affected usually have a normal life span. However, how easy or difficult their life will be, depends on the severity of the symptoms.

How common is CCD?

The exact incidence and prevalence of CCD are unknown, however, 6 out of every 100,000 live births have a congenital myopathy.¹

What is another name for the central core disease?

It is also known as central core myopathy.

Summary

Although CCD has no cure, it is generally a slowly progressing disease or not at all. In all non-curable diseases, early diagnosis is the key factor to managing the symptoms properly and leading more of a normal life. A key message is not to hesitate with symptoms of muscle weakness or motor delay (e.g. when your child starts walking).

Never assume that it is just your specificity. It is always better to check with your clinician if everything is all right. Finally, more clinical trials are required to investigate and develop effective treatments for CCD.