Next Topic Types and Symptoms of Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is generally divided into three types based on when symptoms first appear: late infantile, juvenile, and adult. Each type features differences in enzyme activity, age of symptom onset, and types of symptoms.

Late infantile MLD is the most severe and rapidly progressing type of MLD which usually begins anywhere between 6 months and 3 years of age. Patients generally have no arylsulfatase A (ASA) enzyme activity and a rapid progression of the disorder. This form of MLD usually presents with loss or absence of motor skills and is commonly diagnosed after a developmental milestone has been missed, such as walking, or reverting back to crawling after walking. Initial symptoms may include trouble walking, lack of muscle control, and pain in the limbs. Later on, these children lose the ability to walk, eat, see, hear, and communicate. During the disease course, these children frequently develop seizures, have staring or unresponsive spells, and digestive problems. These patients usually lose their battle with MLD within a few years after symptoms appear. Infantile MLD represents about 40-60% of all MLD cases.

Patients with juvenile MLD develop symptoms any time between 4 and 16 years of age. ASA enzyme activity is low or nonexistent; however, the disease progression is not as rapid as in the late infantile type. Cognitive and behavioral symptoms, such as abnormal behavior, poor school performance, and speech problems, may occur before changes in motor function, such as tremors and difficulty walking, become apparent; however, it is not uncommon for motor function to decline first. Juvenile MLD progresses more gradually than late infantile MLD, and patients can live more than 10 years after symptom onset. Juvenile MLD represents about 25-40% of all MLD cases.

Adult MLD can occur any time after puberty. Most patients have about 2% to 5% of normal ASA enzyme function, which results in a much slower progression of the disorder. The first symptoms to appear are a decline in intellectual abilities, memory loss, disorganized thinking, and psychotic episodes. In many cases, adult MLD is initially mistaken for schizophrenia. Physical symptoms, such as clumsy movements and incontinence, may occur later than the cognitive and behavioral features of the disease. Near the end of the illness, patients develop blindness and lose the ability to move independently. They subsequently experience further neurological and physical impairments before death. Patients with adult MLD can live a long life, sometimes several decades after symptom onset. Adult MLD accounts for about 15-25% of all MLD cases.

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