Congenital muscular dystrophy (CMD) is a group of rare hereditary muscle diseases caused by underlying genetic mutations resulting in muscle weakness with progressive deterioration. The initial symptoms usually occur within the first few months of life or early childhood. The common presenting symptoms include hypotonia, muscle weakness and joint contractures. Some affected children also have breathing difficulty and feeding and swallowing problems due to weakness of the breathing muscles and swallowing muscles.
More than 30 different types of CMD have been reported and the presenting symptoms, disease severity, and rate of disease progression have a wide spectrum. All the affected individuals will have progressive muscle weakness and some of them also have learning difficulties, epilepsy and cardiac problems.
Your doctor will take a detailed history asking you about the onset of your child’s symptoms and how the disease has progressed over time to affect daily performance. If your child is suspected to have CMD, the following investigations will be helpful to provide some important information to confirm the diagnosis. Muscle enzyme levels (Creatine Kinase) will be checked and electromyography study will be arranged. Muscle biopsy will provide helpful clues on the possible subtype of CMD to guide the genetic diagnosis.
Based on the muscle biopsy and the genetic study findings, the CMD can be classified into different subtypes. The more common subtypes are as followed:
(1) 1) Alpha-dystroglycanopathy or muscular dystrophy with abnormal glycosylation of the alpha-dystroglycans
Abnormal glycosylation of the alpha-dystroglycan can cause muscular dystrophies of variable onset and severity. This congenital muscular dystrophy subtype is usually more severe, with abnormalities not only limited to the muscles, but also involving the brain and eyes, causing neurological and visual problems. Some of the most severely affected babies may die within the first year of life. Those who present as limb girdle muscular dystrophy are at the mild end of the spectrum and usually will not have intellectual or eye problems. Currently, more than 10 genes have been identified causing the alpha-dystroglycanopathy.
(2) Merosin deficient congenital muscular dystrophy
(3) Collagen VI-related dystrophy
Collagen VI-related myopathy is caused by the deficiency of collagen VI in the myomatrix of the muscles. The mild end of the disease spectrum is Bethlam myopathy, while the severe end is Ullrich congenital muscular dystrophy. All the children have normal intelligence and their creatine kinase levels are usually normal. This condition is caused by the underlying mutations of three major collagen VI genes including COL6A1, COL6A2, COL6A3.
(4) Rigid spine syndrome
Affected individuals often present initially as motor delay. For example, they will roll over, sit up and walk at a much later age than their peers. Some of the more severely affected children may not be able to achieve some of the motor milestones mentioned above. As the child grows, their muscle weakness and joint contractures will increase, causing more motor difficulties or even loss of ambulation, as well as secondary complications like scoliosis or respiratory insufficiency.
Those with milder presentation and later onset of symptoms will have a better prognosis and their lifespan are not affected and is similar to the average person. More severe congenital muscular dystrophy with early severe presentation and other systems, such as brain and heart involvement will have a higher morbidity and mortality due to the severe disease presentation and progression.
Currently, there is no curative treatment for congenital muscular dystrophy. However, there is a standard of care and treatment that includes a multi-disciplinary team to follow-up the affected children and to provide the therapy and intervention needed to improve their general health, performance and participation.
The children should have regular follow-up by a multidisciplinary team. Upon each follow-up, the vital signs, growth and nutritional status will be monitored. Other important regular evaluations include sleep study, lung function test, muscle strength test and motor function assessment. The affected individual will be referred to an occupational therapist, physiotherapist, dietitian, and clinical psychologist for further recommendation of rehabilitation recommendation and follow-up.
Under more urgent situations, where the affected individuals report respiratory difficulty, poor general states and appetite, unsatisfactory weight gain or even weight loss, or develop seizures, family members or the affected individuals should seek early consultation. If the condition is critical, one should immediately go to the Accident and Emergency Department for treatment.
Musculoskeletal Care:The common muscles and skeletal problems include muscle weakness, joint contractures, joint deformities, joint subluxation or dislocation, and spinal curve (scoliosis). Both the physiotherapist and occupational therapist will provide the information on the regular stretching exercises, the use of splintage to prevent the rapid development of joint contractures, the use of rehabilitation equipment including assistive walking device and standing frame, and special seating arrangements. Sometimes, the children will need orthopaedic surgery to correct the joint dislocation or significant scoliosis.
Pulmonary Care:Affected individuals with congenital muscular dystrophy will develop early respiratory insufficiency due to significant respiratory muscle weakness. The deterioration of the spinal curve also compresses on the chest wall further and deteriorates respiratory function. The doctor will arrange regular lung function tests to follow-up the breathing effort of the affected children and individuals. If there is evidence that clearance of sputum is becoming more difficult, or ventilation support is required, the therapists will also teach affected individuals and families on the daily chest physiotherapy and use of cough assist device. If the affected individual requires ventilation support, it usually starts with the use of a non-invasive ventilator for initial night time use during sleep. If the respiratory muscle weakness progresses, the time for the non-invasive ventilation support will be increased and occasionally, changing to invasive ventilation support with direct ventilation through tracheostomy may be considered. Individuals with congenital myopathy are more prone to developing respiratory complications during respiratory tract infection. Therefore, they are recommended to complete their immunization schedule and to receive yearly seasonal flu vaccination.
Epilepsy Management:Epilepsy is not uncommon in individuals with severe congenital muscular dystrophy. The doctor will arrange several testing (for example, electroencephalogram, MRI brain) to evaluate the seizure problem and the possible underlying cause, and to recommend medical treatment to control the seizures.
Cardiac Care:Certain types of congenital muscular dystrophy can have associated cardiac problems. The common problems include arrhythmia and cardiomyopathy. Affected children or individuals may complain of chest discomfort, easy tiredness, dizziness and even syncope. The doctor will arrange the necessary cardiac evaluation and provide medical treatment to control the heart rate and the heart function. Some of the patients with irregular heart rate problem may even need the implantation of a device.
Nutritional Care:Because of the weak oral and pharyngeal muscles, children or individuals with the severe congenital muscular dystrophy often have feeding and swallowing problems, therefore increasing the risk of under nutrition and aspiration with aspiration pneumonia. The doctor will arrange assessment by speech therapist and swallowing study to assess the performance of oral feeding. The dietitian will also recommend the necessary dietary modification to improve the nutritional intake. If oral feeding is unsafe, the child can receive the nutrition intake through a nasogastric tube (for short term use) or gastrostomy feeding.
Special Education:Apart from physical impairment, some children with congenital myopathy also have learning difficulties or related specific learning problems. The doctor will arrange a detailed assessment on their intellectual potential and may refer the child to the Education Bureau for special education support with necessary rehabilitation training support in school.
Psychological Care:Congenital myopathy is a chronic illness that can have negative psychological impact on the affected individuals. Family members who take care of the affected individual often have chronic stress. The doctor will refer the individual or family member to a clinical psychologist for further psychological support and counseling if there is significant stress on the individual or the family.
Palliative Care:The purpose of the palliative care is to improve the affected child’s or individual’s quality of life through management approach that can decrease the painful experience of the affected. Pain management and psychological support are both very important to the affected and the family, especially in situations where the medical condition is critical.
Others:Congenital muscular dystrophy can also lead to other commonly seen problems such as gastroesophageal refluxes, constipation, poor oral hygiene and dental problems. The doctor will provide treatment according to each presenting problem.
Recently, a phase 1 clinical trial on an anti-apoptotic compound omigapil in collagen VI-related dystrophy has been completed and is in the analysis phase.
Congenital muscular dystrophy is caused by genetic mutations. The inheritance is usually autosomal recessive, i.e. each parent as an asymptomatic carrier carries one mutated gene, and their children have ¼ chance to have the congenital muscular dystrophy receiving both mutated genes, one from the father and one from the mother. Sometimes the inheritance can be autosomal dominant. In this situation, the mutation is usually not from the parents but incidentally develop in the child causing the muscular dystrophy presentation. The child, having one mutated gene, can already manifest the disease presentation. If an underlying genetic mutation can be found in the affected child, and the parents have been confirmed as the carrier of the mutated gene, prenatal diagnosis and even pre-implantation genetic diagnosis can be arranged to ensure the next pregnancy is not affected.
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