Metachromatic leukodystrophy is a rare hereditary (genetic) disorder that causes fatty substances (lipids) to build up in your brain, spinal cord and peripheral nerves.

This buildup is caused by a deficiency of an enzyme that helps break down lipids. Your brain and nervous system progressively lose function.

Rarely, a deficiency in another kind of protein (activator protein) causes metachromatic leukodystrophy.

There are four types of metachromatic leukodystrophy. Each type occurs at different ages, but they may overlap. Each has different signs and symptoms.

The types and approximate age ranges include:

• Infantile form, occurring between birth and 12 months of age
• Late infantile form, occurring between a few months and 2 years of age
• Juvenile form, occurring between ages 3 and 16
• Adult form, occurring after age 16