Metachromatic leukodystrophy

Definition

Metachromatic leukodystrophy (MLD) is a genetic disorder that affects nerves, muscles, other organs, and behavior. It slowly gets worse over time.

Alternative Names

MLD; Arylsulfatase A deficiency; Leukodystrophy - metachromatic

Causes, incidence, and risk factors

MLD is usually caused by the lack of an important enzyme called arylsulfatase A. Because this enzyme is missing, chemicals called sulfatides build up in and damage the nervous system, kidneys, gallbladder, and other organs. In particular, the chemicals damage the protective sheaths that surround nerve cells.

The disease is passed down through families (inherited). You must get a copy of the defective gene from both your parents to have the disease. Parents can each have the defective gene, but not have MLD. A person with one defective gene is called a "carrier."

Children who inherit only one defective gene from one parent will be a carrier, but usually will not develop MLD. When two carriers have a child, there is a 25% chance that the child will get both genes and have MLD.

MLD occurs in about 1 in 40,000 people. There are three forms of the disease. They are based on when the symptoms begin:

• Late infantile MLD symptoms usually begin by ages 1 - 2.
• Juvenile MLD symptoms usually begin between ages 4 and 12.
• Adult (and late-stage juvenile MLD) symptoms may occur between age 14 and adulthood (over age 16), but may begin as late as the 40s or 50s.

Symptoms

• Abnormal high muscle tone, abnormal muscle movements
• Behavior problems
• Decreased mental function
• Decreased muscle tone
• Difficulty walking
• Feeding difficulties
• Frequent falls
• Inability to perform normal tasks
• Incontinence
• Irritability
• Loss of muscle control
• Nerve function problems
• Personality changes
• Poor school performance
• Seizures
• Speech difficulties, slurring
• Swallowing difficulty

Signs and tests

Signs include:

• Abnormal eye movements
• Abnormal posture
• Decreased or no deep tendon reflexes
• Coma
• Optic nerve atrophy

Possible tests include:

• Blood or skin culture to look for low arylsulfatase A activity
• Blood test to look for low arylsulfatase A enzyme levels
• CT scan
• DNA testing for the ARSA gene
• MRI
• Nerve biopsy
• Nerve velocity conduction studies
• Urinalysis
• Urine chemistry

Treatment

There is no cure for MLD. Care focuses on treating the symptoms and preserving the patient's quality of life with physical and occupational therapy.

Research is studying techniques to replace the missing enzyme (arylsulfatase A).

Support Groups

For additional information and resources, see:

• United Leukodystrophy Association - www.ulf.org
• MLD Foundation - www.mldfoundation.org

Expectations (prognosis)

MLD is a severe disease that gets worse over time. Eventually people lose all muscle and mental function. Life span varies depending on what age the condition started, but the disease course usually runs 3 - 20 or more years.

People with this disorder are expected to have a shorter-than-normal lifespan. The earlier the age at diagnosis, the more quickly the disease progresses.

Prevention

Genetic counseling is recommended if you have a family history of this disorder.