Congenital Myopathies: Minicore (multicore) myopathy

What is a myopathy?

The term myopathy is derived from the Greek language and it means muscle disorder.
The congenital myopathies are a group of conditions affecting proximal muscles and causing muscle weakness and wasting. Sometimes symptoms are present at birth but at other times they are not recognised until later on in childhood or adult life.

What is minicore (multicore) myopathy?

The name ‘multicore myopathy’ was initially given in 1971, but a few years later the name “minicore myopathy” became the preferred name for this condition. Both names refer to the abnormal structures seen in the affected muscle fibres when looked at under the microscope.

How does the disease present?

The disease usually causes muscle weakness which is mainly proximal- that is, it affects the limb muscles near the trunk, the trunk itself, and the muscles of the face.Most children present with delay in motor development but most infants are able to walk independently around 28 months.Some patients may present earlier with evidence of muscle weakness and swallowing difficulties at birth.

How does the disease progress?

Most patients show a static or only slowly progressive course and retain the ability to walk.

Are the patients at risk of developing scoliosis (spinal curvature)?

Yes they are. Some patients over the age of 10 years develop significant scoliosis.

Are there any other complications?

Breathing difficulties may be seen in some patients especially in older patients and those who have developed significant scoliosis. Sometimes assistance with breathing is required at night time. Heart complications are very infrequent.

Is there a risk with General Anaesthesia?

No, unless the patient has significant breathing difficulties.

Is intelligence affected?

No intelligence is normal.

Is minicore myopathy inherited?

Yes, most cases are autosomal recessive in which case both the parents need to be carriers of the condition and the risk of a child of either sex being affected is 25% (1 in 4).

Very rarely patients may show a different form of inheritance known as autosomal dominant. In this type one (either) of the two parents is affected, maybe only mildly so, but carries the abnormal gene, and each child (of either sex) of that affected parent has a 50% (1 in 2) chance of being affected.

Some cases are “sporadic” which means they occur randomly, or as a one off, with very little risk to other children in the family being affected. However, people who are themselves sporadic cases will be at risk of passing on the condition to their children.

How is minicore myopathy diagnosed?

The diagnosis of a “myopathy” is usually suspected from the patient’s medical and family history and examination. However the specific diagnosis of minicore myopathy is nearly always made by looking at a piece of muscle (muscle biopsy). Before doing a muscle biopsy (which involves taking out a small piece of muscle usually from the thigh muscle) a few other tests may be done, one of which is a blood test which measures the level of a muscle enzyme (creatine kinase or CK level), which is usually normal but may be slightly high.

The other is an electrical test of the muscles and the nerves supplying the muscle; it involves placing a fine needle into the muscle, which then measures the electrical activity arising from that muscle. Although this test may be able to show a ‘myopathic’ pattern of abnormal muscle activity (seen in any myopathy) it is unable to define the exact type. The muscle biopsy is therefore the important test, which will make the diagnosis. The muscle in this condition shows evidence of abnormal ‘minicores’, which are scattered randomly in the muscle.

Is the genetic defect known in minicore myopathy?

No, the genetic defect has not yet been identified in this type of myopathy.

Is there a treatment or a cure?

At the moment there is no cure, nor any drug treatment for minicore myopathy. However, other very helpful measures can be taken such as physiotherapy (see below), the use of antibiotics to treat chest infections, or naso-gastric tube feeding when necessary.

Is the condition progressive?

The condition is usually non-progressive or slowly progressive. In general the earlier the onset of the disease the more severe and progressive the disorder is. In most cases however, the disease is only slowly progressive. A few patients may eventually lose the ability to walk. Occasionally muscle weakness may progress quite rapidly and these patients experience serious breathing problems.

What help can be offered?

Physiotherapy is one of the main forms of help. An exercise programme and regular check-ups should follow an initial physiotherapy assessment at the time of the diagnosis. The main aim of physiotherapy is to keep the muscles as active as possible to prevent the formation of ‘contractures’ (muscle tendon tightness causing restriction in the range of joint movement). It is also important to provide good seating and to ensure a proper sitting and standing posture to prevent scoliosis (curvature of the spine). The other role of physiotherapy is to help with provision of appliances such as splints, calipers, standing frames (mechanical aids helping to keep children on their feet) and wheelchairs where necessary.

Children and adults are encouraged to remain as active as possible and ensure that they do not become overweight to limit the strain imposed on their weak muscles. Swimming is a particularly good form of exercise.