|
|
Metachromatic Leukodystrophy (MLD)
is one of a group of genetic disorders called the leukodystrophies. These
diseases impair the growth or development of the myelin sheath, the fatty
covering that acts as an insulator around nerve fibers. Myelin, which
lends its color to the white matter of the brain, is a complex substance
made up of at least 10 different enzymes. The leukodystrophies are
caused by genetic defects in how myelin produces or metabolizes these enzymes.
Each of the leukodystrophies is the result of a defect in the gene that
controls one (and only one) of the enzymes. MLD is caused by a deficiency
of the enzyme arylsulfatase A. MLD is one of several lipid storage
diseases, which result in the toxic buildup of fatty materials (lipids)
in cells in the nervous system, liver, and kidneys. There are three
forms of MLD: late infantile, juvenile, and adult. In the late infantile
form, which is the most common MLD, affected children have difficulty walking
after the first year of life. Symptoms include muscle wasting and
weakness, muscle rigidity, developmental delays, progressive loss of vision
leading to blindness, convulsions, impaired swallowing, paralysis, and
dementia. Children
may become comatose. Most children with this form of MLD die by age
5. Children with the juvenile form of MLD (between 3-10 years of
age) usually begin with impaired school performance, mental deterioration,
and dementia and then develop symptoms similar to the infantile form but
with slower progression. The adult form commonly begins after age
16 as a psychiatric disorder or progressive dementia. Adult-onset MLD progresses
more slowly than the infantile form. |