What is Metachromatic Leukodystrophy?

Metachromatic Leukodystrophy (MLD) is a rare genetic disorder caused by the accumulation of fats called sulfatides inside of the cells. MLD mainly affects cells of the central nervous system. High levels of sulfatide within cells of the nervous system can cause the destruction of myelin, a substance that protects and insulates nerves. Patients with MLD usually experience abnormal muscle rigidity and movement, along with the inability to walk, seizures, and several developmental and mental impairments. 


The prevalence rate is estimated to be between 1 in 40,000 and 1 in 160,000. However, disease prevalence can be higher in certain groups, like the Navajo Nation and some Middle Eastern populations.  

Types of MLD

There are three forms of MLD, each characterized by the age of onset of the disease. 


While there are different forms, common symptoms include:
Late Infantile MLD:

Juvenile MLD

Adult MLD


MLD is an autosomal recessive genetic disorder, so an abnormal copy of the gene from each parent must be passed to the child for the disease to develop. It is caused by a mutation or change in the gene that produces the enzyme arylsulfatase A (ASA). MLD can also be caused by other defective proteins, like Saposin B, which is needed for proper ASA function.  
ASA is essential for the breakdown of a type of fats called sulfatides. Low levels or low activity of ASA lead to the accumulation of sulfatides in the nervous system and other organs. High levels of sulfatides in the nervous system disrupts the production and the structure of myelin by destroying myelin-producing cells. Demyelination (damage that destroys the myelin sheath that surrounds the nerves) exposes the nerve cell and negatively affects the nerve cell’s ability to communicate with other cells.  

MLD is also known as a Lysosomal Storage Disorder, because ASA is usually located inside lysosomes. Lysosomes are the part of the cells in charge of breaking down unnecessary molecules in the cells. In MLD, ASA is meant to degrade sulfatides.     

Current Treatments

There are currently no effective traditional methods of treatment, as most therapies focus on managing the symptoms. This brings to light a great need for new and effective investigational therapies, including stem cell transplantation, enzyme replacement studies, and investigative gene therapy trials. 

You can contact us for more information about the possibility to participate in a clinical trial for MLD.  

Recommended Resources

MLD Foundation

National Organization for Rare Disorders

United Leukodystrophy Foundation


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