What is Metachromatic Leukodystrophy?
Metachromatic leukodystrophy (MLD) is an inherited genetic disease which damages the nervous system. People with MLD will progressively lose intellectual and motor functions. Symptoms may include spasticity, seizures, personality changes, and progressive dementia. As the disease progresses, the person loses the ability to walk, talk, see, and hear. Eventually he or she become paralyzed and unresponsive.
MLD is the most common in a group of diseases known as leukodystrophies. These diseases affect the myelin sheath, a fatty covering that insulates and protects nerve cells.
MLD results from a deficiency in an enzyme called arylsulfatase A. The lack of arylsulfatase A causes a fatty substance called sulfatide to build up to toxic levels in the body. This gradually destroys the myelin sheath, without which brain cells die and nerves in the body cannot function properly.
Metachromatic leukodystrophy can be divided into early-onset and late-onset forms. The early-onset form is also called the infantile form, and the late-onset form can be further divided into juvenile or adult forms. The course of the disease is similar, but the age at which symptoms appear varies, as does the rate at which symptoms progress. The age at which symptoms begin is usually similar among family members.
This is the most common form of MLD, accounting for 50-60% of all cases. Symptoms appear between the first and second years of life. Initially, affected children lose any language abilities they have developed and have trouble walking. Gradually their muscles waste away and become rigid. They will lose mental function and often experience seizures and loss of sensation in their limbs. By the final stages of the disease, children with infantile MLD become blind and deaf and require a feeding tube. They are unresponsive to their surroundings and become paralyzed. Infantile MLD is usually fatal by the age of 10.
In the juvenile form of MLD, symptoms appear after the age of 3 but before adolescence (12 to 14). Between 20-30% of people with MLD have the juvenile form. Initial signs of the disease are often difficulties in school and behavioral problems. Clumsiness, slurred speech, incontinence, and strange behavior often prompt parents to seek a diagnosis. As the disease continues, symptoms are similar to infantile MLD, but progress more slowly. The disease is usually fatal 10 or 20 years after symptoms appear.
In the adult form of MLD, symptoms appear after puberty and may not appear until a person’s 40s or 50s. Roughly 15 to 20% of people with MLD have the adult form. Early signs of the disease often include personality changes, problems at school or work, numbness in the extremities of one’s limbs, muscle weakness and loss of coordination, psychiatric problems such as delusions or hallucinations, or drug and alcohol abuse. It can be initially misdiagnosed as schizophrenia, depression, or multiple sclerosis.
Over time, an affected person’s behavior will grow inappropriate and he or she will have trouble making good decisions. Everyday skills become difficult and movement will grow spastic and awkward. Eventually a person affected by the adult form will lose the ability to carry on a conversation. In the final stages of the disease, symptoms are similar to the infantile form—blindness, deafness, unresponsiveness, and paralysis.
This form of the disease progresses more slowly than the other forms. Those affected may experience periods of stability or periods of particularly rapid decline. People with the adult form of MLD may live 20 or 30 years after their initial diagnosis.
How common is Metachromatic Leukodystrophy?
Worldwide, 1 in every 40,000 to 160,000 people have metachromatic leukodystrophy. In certain populations, the prevalence can be much higher. These populations include Habbanite Jews in Israel (1 in 75), Israeli Arabs (1 in 8,000), Christian Israeli Arabs (1 in 10,000), and those in western portions of the Navajo Nation (1 in 2,500).
How is Metachromatic Leukodystrophy treated?
There is no cure for MLD. Bone marrow transplantation may be an option for some people with MLD. It has shown the most promise in people who are not yet showing symptoms of MLD. At best it slows, but does not stop, the progression of the disease. This is a controversial treatment because of its substantial health risks.
Other treatments aim to manage symptoms of the disease as they arise. Seizures and muscle tightness may be treated with medication. Physical therapy may help preserve movement as long as possible. Also helpful may be walking aids, wheelchairs, and feeding tubes.
What is the prognosis for a person with Metachromatic Leukodystrophy?
All people with metachromatic leukodystrophy will experience mental and motor deterioration, eventually reaching a state of paralysis and unresponsiveness.
Most children with the infantile form die by the age of 10. Those with the juvenile form typically develop symptoms between the ages of 3 and 14 and can live 10 to 20 years after the onset of symptoms. The adult form of the disease is more variable, but affected adults may not develop symptoms until their 40s or 50s and can live 20 to 30 years after symptoms begin. Death most commonly occurs from pneumonia or other infections.