Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare genetic condition that leads to damage to the white matter of your central nervous system (brain and spinal cord) and peripheral nerves. MLD is one of several lysosomal storage diseases.

White matter damage happens when fatty materials called sulfatides build up in your cells. The buildup impairs the growth of the myelin sheath (the protective covering around nerve fibers). Myelin gives white matter its color.

This damage causes a decline in mental and motor (muscle movement) functions. Symptoms of MLD get worse over time, and usually results in death years after diagnosis.

Metachromatic leukodystrophy gets its name from the way cells with a buildup of sulfatides appear when you look at them under a microscope. The sulfatides appear metachromatic, which means they pick up color differently than the surrounding cellular material when a pathologist stains them for examination. “Leukodystrophy” means progressive destruction of white matter (“leuko” means “white” and “dystrophy” means “wasting away”).

Forms of MLD

Metachromatic leukodystrophy has three distinct forms:

• Late infantile MLD: This form typically affects babies who are between 12 and 20 months old. It causes walking issues, developmental delays, blindness and dementia. Most children with late infantile MLD die by age 5. Late infantile MLD is the most common form of MLD, representing 50% to 60% of cases.
• Juvenile MLD: This form affects children between the ages of 3 and 10. It causes intellectual decline, behavioral difficulties, seizures and dementia. Juvenile MLD typically results in death 10 to 20 years following diagnosis. Around 20% to 30% of people with MLD have this form.
• Adult MLD: This form typically begins after the age of 16. Symptoms include psychiatric changes, seizures and dementia. It usually results in death within six to 14 years after diagnosis. About 15% to 20% of people with MLD have this form.

How rare is metachromatic leukodystrophy?

MLD is rare. Researchers estimate that it affects 1 in every 40,000 people in the United States. MLD may be more common in certain isolated populations. For example, the Navajo have a higher prevalence rate of 1 in every 2,500 people.