Congenital Muscular Dystrophies

Congenital muscular dystrophy, also known as “CMD”, refer to a group of heterogeneous genetic conditions that become apparent at birth (congenital) or early during infancy (usually before 1 year old) with a common muscle pathology. Primarily affecting voluntary muscles, they are characterized by diminished muscle tone (hypotonia) and poor motor skills, with a noticeable ‘floppiness’, progressive muscle weakness (atrophy), and contractures in the angles, hips, knees and elbows.  It is estimated to affect around 1 in every 20,000 to 50,000 live births.  However, the figures may be underestimated due to the difficulty in diagnosis CMD.

Classification

1. By pathogenic variants

   CMD is a general term for a group of genetic muscle diseases. There are a number of proposed methods for classifications, which are updated on an on-going basis. One way is to classify these diseases by how their faulty protein affects cells. Under this classification, over 30 different CMD disorders have been recognized; the more commonly known ones include: - 

   • Collagen VI deficient CMD --Ullrich congenital muscular dystrophy (severe form), Bethlem myopathy (mildest form);
   • Merosin-deficeint CMD;
   • Dystroglycanopathies -- Fukuyama congenital muscular dystrophy; muscle-eye-brain disease; Walker-warburg syndrome;
   • LMNA-related disorders;
   • Rigid spine muscular dystrophy (RSMD1) -SEPN1-related disorders,

   The most common forms of the condition from overseas studies are Ulrich congenital muscular dystrophy, which affects about 50 percent of CMD subjects, and merosin- deficient congenital muscular dystrophy, which affects 25 percent.

2. By clinical symptoms

   Clinically, they are generally grouped under two main types:
   

   1. Children who have only generalized muscle weakness and with normal intelligence;
   2. Children who have muscle weakness and learning difficulties, with or without seizures. Learning difficulties may be subtle, moderate or severe.

Symptoms

CMD has its onset at or near birth, resulting in overall muscle weakness and poor motor control, including the inability to sit or stand without support. Other common signs are contractures in the ankles, hips, knees and elbows. The contractures can sometimes be severe and affect several joints.

CMDs belong to a larger group of muscular dystrophy disorders. As CMD babies get older, the symptoms, the degree of severity and rate of progression can vary greatly amongst different CMD disorders. Potential complications include spinal curvature (scoliosis), respiratory complications at birth, intellectual disabilities, learning disabilities, eye defects or seizures, or feeding problems due to weakness of oromotor muscles.

Cause

CMD is caused by genetic mutations which affect the production of important muscle proteins. 

Treatment

At the moment, there is no curative treatment for CMD. However, many of the genes responsible for protein have been identified. Management is specifically made to an individual’s needs by a multidisciplinary team. There are therapies available to assist the child to grow and develop, improve the quality of life, and reduce the risk of associated complications and early death. These include:

• Physical and occupational therapy, including gentle exercise, splints or braces to treat spinal and limb contractures;
• Special nutritional and dietary needs for those underweight;
• Monitoring and treatment of heart conditions and breathing problems;
• Monitoring and treatment of stomach complications e.g. reflux and constipation  
• Speech therapy and swallowing studies;
• Orthopedic therapy or surgery for bone weakness and scoliosis.