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Metachromatic leukodystrophy occurs when the body lacks enzymes needed to break down a certain lipid.
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Symptoms vary depending on whether the child has the infantile form or the juvenile form but may include paralysis, dementia, and nerve problems.
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The diagnosis may be made by doing prenatal screening tests, nerve conduction studies, and blood and urine tests.
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This disease causes premature death.
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This disease cannot be treated or cured, but treatment options are being studied.
There are different types of inherited disorders. In metachromatic leukodystrophy, both parents of the affected child carry a copy of the abnormal gene. Because usually two copies of the abnormal gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders.)
Sphingolipidoses occur when people do not have the enzymes needed to break down (metabolize) sphingolipids, which are compounds that protect the cell surface and serve certain functions in the cells. There are many types of sphingolipidoses besides metachromatic leukodystrophy:
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Gaucher disease (most common)
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Niemann-Pick disease (types A and B)
In metachromatic leukodystrophy, an enzyme needed to break down a certain lipid, called arylsulfatase A, is not working correctly. This lipid builds up in the white matter of the brain and spinal cord, nerves, kidneys, spleen, and other organs. This buildup results in demyelination. Demyelination is the destruction of the tissue that wraps around nerves, called the myelin sheath. When the myelin sheath is damaged, nerves do not conduct electrical impulses normally. When impulses are not conducted normally, movements are jerky, uncoordinated, and awkward.
Types of metachromatic leukodystrophy
In the infantile form, a child has progressive paralysis and dementia, meaning that the paralysis and dementia get worse throughout the life of the child. Symptoms of this form usually begin before 4 years of age and result in death by about age 9.
In the juvenile form, children have problems walking, intellectual impairment, and weakness, numbness, and pain in the hands and feet. Symptoms of this form begin between 4 years and 16 years of age.
There is also a milder adult form.
Diagnosis
Before birth, metachromatic leukodystrophy may be diagnosed in the fetus by using the prenatal screening tests chorionic villus sampling or amniocentesis.
After birth, doctors do nerve conduction studies to measure the speed at which nerves conduct impulses. Blood and urine tests are also done. Doctors do the imaging tests computed tomography (CT) or magnetic resonance imaging (MRI) of the brain to look for signs of damage to the myelin sheaths.
Doctors also measure levels of arylsulfatase A in white blood cells or skin cells. Genetic testing, which is used to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder, is also available.
Treatment
This disease cannot be cured at the present time. However, bone marrow transplantation or stem cell transplantation may help people who have mild forms of the disease.
Enzyme replacement therapy and gene therapy are possible treatment options that are being studied.
