Metachromatic leukodystrophy (MLD) is a genetic disorder that affects nerves, muscles, other organs, and behavior. It slowly gets worse over time.
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.
Abnormal high muscle tone, abnormal muscle movements
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.
Genetic counseling is recommended if you have a family history of this disorder.
Chad Haldeman-Englert, MD, Wake Forest University School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.