What is Metachromatic Leukodystrophy?
Metachromatic leukodystrophy (MLD) is one of a group of genetic disorders called the leukodystrophies. These are diseases that impair the growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fiber. Myelin, which lends its color to the white matter of the brain, is a complex substance made up of at least ten different chemicals. The leukodystrophies are caused by genetic defects in how myelin produces or metabolizes these chemicals. Each of the leukodystrophies is the result of a defect in the gene that controls one (and only one) of the chemicals. MLD is caused by a deficiency of the enzyme arylsulfatase A. There are three forms of MLD: late infantile, juvenile, and adult. In the late infantile form, which is the most common, affected children have difficulty walking after the first year of life. Symptoms include hypotonia (low muscle tone), speech abnormalities and loss of mental abilities, blindness, rigidity (uncontrolled muscle tightness), convulsions, impaired swallowing, paralysis, and dementia. Children with this form of MLD become bedridden, blind, and enter a vegetative state. They usually die in the first decade. Those with the juvenile form (between 3-10 years of age) usually begin with emotional disturbances and dementia and then develop symptoms similar to the infantile form but with slower progression. In the adult form, MLD commonly begins around age 30 as a psychiatric disorder or progressive dementia. The illness runs a long course, usually averaging 15 years.

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