Metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease which is commonly listed in the family of leukodystrophies as well as among the sphingolipidoses as it affects the metabolism of sphingolipids. Leukodystrophies affect the growth and/or development of myelin, the fatty covering which acts as an insulator around nerve fibers throughout the central and peripheral nervous systems. MLD involves cerebroside sulfate accumulation. Metachromatic leukodystrophy, like most enzyme deficiencies, has an autosomal recessive inheritance pattern. Like many other genetic disorders that affect lipid metabolism, there are several forms of MLD, which are late infantile, juvenile, and adult. In the late infantile form, which is the most common form of MLD (50–60%), affected children begin having difficulty walking after the first year of life, usually at 15–24 months. Symptoms include muscle wasting and weakness, muscle rigidity, developmental delays, progressive loss of vision leading to blindness, convulsions, impaired swallowing, paralysis, and dementia. Children may become comatose. Untreated, most children with this form of MLD die by age 5, often much sooner. Children with the juvenile form of MLD (onset between 3 and 10 years of age) usually begin with impaired school performance, mental deterioration, and dementia, then develop symptoms similar to the late infantile form but with slower progression. Age of death is variable, but normally within 10 to 15 years of symptom onset. Some patients can live for several decades after onset. A recent trend is to try to distinguish early-juvenile (ages 3–7) and late-juvenile forms of the disease. Generally early-juveniles have motor skill declines as their first symptoms while late-juveniles show cognitive declines first. The adult form commonly begins after age 16 often with an onset in the 4th or 5th decade of life and presents as a psychiatric disorder or progressive dementia. Adult-onset MLD usually progresses more slowly than the late infantile and juvenile forms, with a protracted course of a decade or more.