Metachromatic leukodystrophy (MLD)?
Metachromatic leukodystrophy is an inherited disorder characterized by the accumulation of fats called sulfatides in cells. This accumulation especially affects cells in the nervous system that produce myelin, the substance that insulates and protects nerves. Nerve cells covered by myelin make up a tissue called white matter. Sulfatide accumulation in myelin-producing cells causes progressive destruction of white matter (leukodystrophy) throughout the nervous system, including in the brain and spinal cord (the central nervous system) and the nerves connecting the brain and spinal cord to muscles and sensory cells that detect sensations such as touch, pain, heat, and sound (the peripheral nervous system).
Sign and Symptoms?
Like many other genetic disorders that affect lipid metabolism, there are several forms of MLD, which are late infantile, juvenile, and adult.Palliative care can help with many of the symptoms and usually improves quality of life and longevity.Carriers have low enzyme levels compared to their family population ("normal" levels vary from family to family) but even low enzyme levels are adequate to process the body's sulfatide. Metachromatic leukodystrophy gets its name from the way cells with an accumulation of sulfatides appear when viewed under a microscope. The sulfatides form granules that are described as metachromatic, which means they pick up color differently than surrounding cellular material when stained for examination.
How common is the disease?
Metachromatic leukodystrophy is reported to occur in 1 in 40,000 to 160,000 individuals worldwide.
What gene are related to MLD?
Most individuals with metachromatic leukodystrophy have mutations in the ARSA gene, which provides instructions for making the enzyme arylsulfatase A. This enzyme is located in cellular structures called lysosomes, which are the cell's recycling centers. Within lysosomes, arylsulfatase A helps break down sulfatides. A few individuals with metachromatic leukodystrophy have mutations in the PSAP gene. This gene provides instructions for making a protein that is broken up (cleaved) into smaller proteins that assist enzymes in breaking down various fats. One of these smaller proteins is called saposin B; this protein works with arylsulfatase A to break down sulfatides. Mutations in the ARSA or PSAP genes result in a decreased ability to break down sulfatides, resulting in the accumulation of these substances in cells. Excess sulfatides are toxic to the nervous system. The accumulation gradually destroys myelin-producing cells, leading to the impairment of nervous system function that occurs in metachromatic leukodystrophy. In some cases, individuals with very low arylsulfatase A activity show no symptoms of metachromatic leukodystrophy. This condition is called pseudoarylsulfatase deficiency.
How do people inherit MLD-?
MLD has an autosomal recessive inheritance pattern. which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition
There is currently no treatment or cure for MLD. Children with advanced juvenile or adult onset and late infantile patients displaying symptoms receive treatment limited to pain and symptom management. Presymptomatic late infantile MLD patients, as well as those with juvenile or adult MLD that are either presymptomatic or displaying mild to moderate symptoms, have the option of bone marrow transplantation (including stem cell transplantation), which is under investigation to see if it may slow down progression of the disease or stop its progression in the central nervous system. However, results in the peripheral nervous system have been less dramatic, and the long-term results of these therapies have been mixed. Recent success has involved stem cells being taken from the bone marrow of children with the disorder and infecting the cells with a retro-virus, replacing the stem cells mutated gene with the repaired gene before re-injecting it back into the patient where they multiplied. The children by the age of five where all in good condition and going to kindergarten when normally by this age, children with the disease can not even speak. Several future treatment options are currently being investigated. These include gene therapy, enzyme replacement therapy (ERT), substrate reduction therapy (SRT), and potentially enzyme enhancement therapy (EET). A team of international researchers and foundations gathered in 2008 to form an international MLD Registry to create and manage a shared repository of knowledge, including the natural history of MLD. This consortium consisted of scientific, academic and industry resources. This registry never became operational.
Other name of this condition-
When to contact a Medical Professional?
Who to contact for more information?
The Department of Health Research and Indian Council of Medical Research have constituted a National Task Force to perform a multicentric collaborative study at different research institutes across the country. Further information can be found at http://www.icmrmetbionetindia.org/task-force-disoredrs.php
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Dr Seema Kapoor
Maulana Azad Institute of Medical Sciences, New Delhi