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Merosin-Negative CMD
Children with merosin-negative
(CMD) lack all or part of the muscle protein merosin (also known as laminin
alpha 2). The degree of muscle weakness can range from severe (never walking) to
mild (walking at 2 to 3 years) it depends on how much merosin protein a child is
making. 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 is usually 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.