Children with MLD appear normal at birth. During the first months, or even years, of the child's life, growth and development take place as though the he/she were an average infant. Functional motor skills such as walking then begin to deteriorate as the disease takes hold. These children seem to progress rapidly over a period of several months -- alternating between stabilization and rapid decline. Independence is quickly lost, and the child becomes bedridden. Seizures are often seen, but they soon disappear. Full body contractions are very common, and appear quite painful to the child. Probably the most painful realization is that the child may still express emotion at this stage. S/he is still able to smile, cry, and respond to the devastated on-looking parents. Soon after this stage the infant loses its sight. A state of general unresponsiveness sets in as more and more body-functions are lost. A feeding tube is often used to maintain nutrition now that swallowing has grown impossible. Months, or perhaps days later infections such as pneumonia begin to run rampant through the victim's body. Death often follows an infection such as this. As more and more modern treatments become available, a child suffering from late infantile Metachromatic Leukodystrophy may survive for many years, but in general the prognosis is not a good one.

    Juvenile onset MLD is characterized by the appearance of symptoms between the ages of 4 and 12. Diagnosis occurs most often during the early years of schooling when there is a noticeable decline in intellectual performance. Juvenile patients have difficulty following directions, show behavioral abnormalities, have periods of incontinence, slur their words, and show difficulty controlling and coordinating their gate.  As the disease progresses, as seen in infantile MLD, seizures begin to occur and full body contractions cause significant pain to the child. The ability to walk is eventually lost, causing patients to become bedridden. The final stages of juvenile onset MLD are similar to those observed in late infantile form.

   The initial symptoms of MLD may be seen in adult onset patients after sexual maturation. Patients have been diagnosed with this form as early as 14 years old and as late as in their 60's. A change in personality or a decrease in job performance are the most common indications that these individuals have fallen victim to MLD.  It is common that those with adult-onset MLD get diagnosed with psychiatric disorders such as late-onset schizophrenia or depression. There is a high rate of comorbidity between MLD patients and alcohol or drug abuse. Adult MLD strips its hosts of cognitive and motor functions over a period of 1 - 3 decades. This slower acting form improves a patients prognosis significantly when compared to the other two subtypes.