This form of CMD is characterized by onset before 1 year of age, with prominent neck weakness and poor head control. After some initial improvement, children gradually develop (by 3 to 7 years) stiffness or rigidity of the spine. To a lesser extent, contractures of limb muscles are seen.
By the teens, the respiratory muscles are affected, while limb muscle strength is less affected. Intellectual function is normal.
Fukuyama congenital muscular dystrophy is seen almost exclusively in those of Japanese descent. The disorder has been linked to a defect in a gene called fukutin, and the most common mutation is thought to have arisen in a single Japanese ancestor many years ago. Evidence suggests that fukutin participates in the sugar coating of dystroglycan.
Muscle weakness in FCMD ranges from severe to mild, and people with the mildest cases are able to walk with assistance. Extensive brain abnormalities are usually accompanied by mental retardation, epilepsy, visual loss and reduced life expectancy (about 11 to 16 years of age).
Muscular dystrophy due to fukutin mutations also can be classified as a form of limb-girdle muscular dystrophy (LGMD). It's known as LGMD2M.
Children who lack a muscle protein called integrin have hypotonia (lack of muscle tone) and weakness early in infancy associated with delayed milestones. They usually don’t walk until age 2 to 3.
Children with merosin-deficient CMD lack all or part of the muscle protein merosin, also called laminin 2 (see Causes/Inheritance). The disease commonly makes itself known when a child fails to learn to walk.
The degree of muscle weakness can range from profound (never walking) to mild (walking at 2 to 3 years), and depends on how much merosin protein a child has.
This form of CMD progresses very slowly or, in some cases, not at all. Special problems include contractures, difficulty breathing and seizures (in 20 percent of cases). Intelligence usually is normal, but learning disabilities have been documented.
A distinctive diagnostic feature of this type of CMD is found by magnetic resonance imaging (MRI). These brain images show changes in the white matter, which consists of nerve fibers that carry messages from the brain to the spinal cord. Despite the appearance on the MRI, those with merosin-negative CMD have few signs of brain impairment in everyday life.
This rare form of CMD, first described in Finland, shares features with Fukuyama CMD. Generally it’s milder, with survival ranging from early childhood to the seventh decade. It’s accompanied by delayed motor milestones, profound mental retardation and vision problems.
Clinical characteristics of Ullrich CMD (or Ullrich’s disease) include hypotonia (loss of muscle tone), hyperlaxity (loose joints) in the hands and feet, and multiple joint contractures at birth, with rigidity of the spine. The course is slowly progressive, causing muscle weakness and wasting (shrinking of muscle size).
Intelligence is normal. Children with Ullrich’s disease may develop respiratory failure during sleep in the first decade of life.
Ullrich's disease and Bethlem myopathy are both caused by abnormalities in or deficiencies of the collagen 6 protein. Ullrich's disease is generally more severe.
This very rare form of CMD is similar to, but more severe than, muscle-eye-brain disease (MEB). Experts consider MEB and WWS to be a spectrum of disorders.
People with this disorder have hypotonia (lack of muscle tone) and seizures. Profound mental retardation and multiple vision problems are encountered. The disorder is usually fatal in infancy.