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Term / Metachromatic Leukodystrophy (MLD)

Leukodystrophy refers to a group of more than 15 rare genetic disorders that cause progressive degeneration of the white matter of the brain due to imperfect growth or development of the myelin sheath, the fatty covering that acts as an insulator around nerve fiber. The leukodystrophies are often referred to as “demyelinating” diseases.

Myelin insulates nerve cells in the brain and spinal cord, helping them to transmit electrical nerve signals. Damage to this insulation slows down or blocks messages between the brain and the rest of the body. Without myelin, nerve cells cease to function and eventually die.

Metachromatic leukodystrophy (MLD) is a genetic disorder that affects organs, nerves, muscles and behavior. 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 myelin sheath that surround nerve cells. MLD is diagnosed in 1 of about every 40,000 people.

There are three forms of the disease, based on when symptoms begin:

  • Late infantile MLD symptoms usually begin by age 1 or 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 may include:

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

There is currently no cure for MLD, which worsens over time. Eventually people lose all muscle and mental function. Life span varies depending on the age at which symptoms appear. The earlier the age at diagnosis, the more quickly the disease progresses. Care focuses on treating the symptoms and preserving the patient’s quality of life with physical and occupational therapy.

The most common leukodystrophies include Canavan disease, Krabbe disease, metachromatic Leukodystrophy (MLD), Childhood Ataxia with Central Nervous System Hypomyelination (CACH), Alexander disease and Refsum disease.

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