Congenital muscular dystrophy

The congenital muscular dystrophies are a group of conditions that share an early presentation and a common muscle pathology. Congenital means ‘from birth’ and in the great majority of cases of congenital muscular dystrophy, the initial symptoms are present at birth or in the first few months.

Babies with congenital muscular dystrophy often have hypotonia (low muscle tone or floppiness) and may have reduced movements. Other common signs are contractures (tightness) of the ankles, hips, knees and elbows. Rarely, contractures can be severe and affect several joints (known as arthrogryposis). Contractures occur because the baby has not had the muscle strength to move around freely in the womb. Some babies with congenital muscular dystrophy may also have respiratory problems owing to weakness of breathing muscles.

In some children who do not have contractures, the first problems are noted only after a few months because of difficulties in holding the head up, or delays in learning how to sit unaided, to stand or walk.

There are many subtypes of CMD. We have specific factsheets on the following subtypes:

• Bethlem myopathy
• Merosin-deficient congenital muscular dystrophy
• SEPN1-related myopathy
• Ullrich congenital muscular dystrophy

The condition is usually fairly stable as far as the muscle power in the legs and arms is concerned, and often the child appears to gain strength in the first decade of life. In several forms of congenital muscular dystrophy, the acquisition of new skills – over time –is possible, although some motor difficulties will always be present, depending on how severe the condition was at presentation.

In many congenital muscular dystrophy subtypes, muscle weakness can increase with time and can lead to respiratory problems. This may happen in children of various ages and is potentially a very serious complication which, if not recognised, can be life-threatening.

The severity of this condition varies greatly from person to person. As the severity varies even within the same form of congenital muscular dystrophy, it is important not to assume that certain motor developments will or will not take place, but rather to work with children so they can achieve the goals which are within their ability.

Some children will walk, but sometimes this can be delayed until the age of five or older. Leg splints are often used to assist a child to walk. Some children who have achieved independent walking may lose this ability later on because, as they grow older and heavier, the muscles are unable to cope with a greater strain. Other children may not be able to walk at all.

The presence and the severity of other problems depend on the subtype of congenital muscular dystrophy. Some features, however, are generally found in many children with congenital muscular dystrophy, irrespective of the subtype.

As the muscles are weak and mobility is limited, the child may either be born with – or develop – joint ‘contractures’ or tightness. This means that the muscle tendons tighten up, and the child is unable to move the limbs or the joints as freely as a non-affected child can. Physiotherapy can help to prevent or slow the progression of contractures, therefore a programme of exercises should be established with the help of a physiotherapist soon after diagnosis. Hips are commonly affected with contractures and may sometimes be dislocated, which may require treatment with a splint or surgery.

Breathing and feeding problems are commonly observed in some forms of congenital muscular dystrophy but are less frequent in others.

In some subtypes of congenital muscular dystrophy, the function of the brain can be affected and give rise to different degrees of learning difficulties. This complication occurs only in specific subtypes and is not progressive. It will usually be evident in the first year of life, and its severity can vary considerably. However, this complication will not develop at a later stage in children who have average intellectual function.

The congenital muscular dystrophies are a varied group of conditions.

There have been recent developments in research into the genetics of congenital muscular dystrophies, which have resulted in a better understanding of this group of conditions.

The first mutation to be discovered was in the LAMA2 (laminin alpha-2) gene, the gene which carries the information to make a protein called merosin. This form of congenital muscular dystrophy, also known as ‘merosin-deficient congenital muscular dystrophy’ affects approximately 25 percent of the children with congenital muscular dystrophy. More recently, further genes have been identified, and to date we know of at least 30 genes responsible for different forms of congenital muscular dystrophy. In the UK, the most common type of congenital muscular dystrophy is Ullrich congenital muscular dystrophy, followed by merosin-deficient congenital muscular dystrophy. There are various other less common subtypes.

Some cases of congenital muscular dystrophy have genetic causes that have not yet been identified. However, the availability of new genetic technologies has increased the probability that the genes for these conditions will be found.

A baby with congenital muscular dystrophy is usually first diagnosed as a ‘floppy baby’. Doctors can see the symptoms described above, but as these could be owing to a number of different conditions, they have to conduct a series of tests to try to make an accurate diagnosis.

Firstly, a blood test is taken and the level of a muscle protein measured – the creatine kinase (CK) level. In approximately 40 percent of cases of congenital muscular dystrophy, this level is five to 20 times higher than normal.

An electromyography (EMG) test may also be performed. A small needle is inserted into the muscle and the electric activity recorded. This test, which may provide evidence of an abnormal pattern of electric activity in the muscle, is usually not necessary in children who have markedly elevated serum CK.

At this stage, however, even in the cases with high CK levels, abnormal muscle ultrasound and EMG, an additional test that is required in almost every case is a muscle biopsy.

A muscle biopsy can help to identify the subtype of congenital muscular dystrophy to provide a precise diagnosis in several ways:

• when the muscle is studied under the microscope, it will show variation in the size
  of muscle fibres and that some of these fibres are replaced by fat and fibrous tissue
• muscle proteins can be studied in detail with specialised tests. This greatly helps to narrow down the diagnosis.

In the forms of congenital muscular dystrophy in which the gene defect has been identified, genetic tests can provide a definitive diagnosis.

There is currently no cure for the congenital muscular dystrophies, but there are ways of helping to manage the effects of the condition.

As this condition can be managed by timely recognition, professional advice and intervention, it is advisable for individuals with congenital muscular dystrophy to be regularly followed by a paediatric neurologist with expertise in muscle wasting conditions, working as part of a multi-disciplinary team. Review should include monitoring weight, respiratory function, muscle strength and joint range. There are several additional examinations that might be needed, such as overnight sleep studies to monitor the breathing quality during sleep and, in some subtypes, a yearly echocardiogram. In children with respiratory impairment, it is also advisable to reduce the risk of chest infections by giving annual flu immunisations and other vaccinations.

Children and adults with congenital muscular dystrophy should ideally be followed regularly in a specialist neuromuscular clinic, with access to physiotherapy, orthotic, respiratory, orthopaedic, spinal and genetic specialists as needed.