Arylsulfatase A deficiency

Alternative names 
MLD; Metachromatic leukodystrophy

Definition

Metachromatic leukodystrophy is an inherited disease characterized by the absence of the enzyme arylsulfatase A, which causes a material called cerebroside sulfate to accumulate in cells. This is toxic to the cell, especially neurons (the cells of the nervous system) and causes the problems of the disease.

MLD is a member of a class of diseases called lysosomal storage disorders. In these diseases, patients lack a protein needed to metabolize the food we eat.

Causes, incidence, and risk factors

Metachromatic leukodystrophy (MLD) is transmitted as an autosomal recessive trait, which means that a person must inherit the defective gene from both parents to be affected.

MLD has a wide range of symptoms. As with many other storage diseases, there are forms of early and delayed onset (late infant, juvenile, and adult types).

The most common and most severe form is the late infant onset form, which has symptoms such as irritability, decreased muscle tone, muscle wasting, and the loss of the ability to walk in babies who have started walking. The disease progresses to Blindness, seizures, and partial paralysis. Death occurs usually before age 10.

Both the juvenile and adult forms have similar symptoms. In the adult and juvenile forms, psychosis and emotional disturbances are often part of the illness. Patients can be misdiagnosed with a psychiatric disorder before the diagnosis of MLD is made. The juvenile form is fatal within a few years of diagnosis. The adult form may be drawn out over many years.

Symptoms

     
  • irritability  
  • decreased muscle tone  
  • abnormal high muscle tone, spasticity, abnormal muscle movements  
  • falls frequently  
  • decreased intellectual functioning  
  • speech difficulties, slurring  
  • feeding difficulties  
  • swallowing difficulty  
  • nerve function abnormality

Signs and tests
Signs include:

     
  • decreased or absent deep tendon reflexes  
  • abnormal eye movements  
  • poor visual fixation  
  • optic nerve atrophy  
  • decorticate posturing  
  • coma

Tests include:

     
  • nerve velocity conduction studies  
  • MRI  
  • CT scan  
  • lumbar puncture and examination of the cerebrospinal fluid, showing increased CSF total protein  
  • nerve biopsy (usually performed on the sural nerve) showing metachromatic deposits  
  • urine chemistry showing markedly increased sulfatide levels  
  • urinalysis showing metachromatic granules in the urine sediment  
  • culture of skin fibroblasts or white blood cells for decreased arylsulfatase A activity

Treatment
At present, there is no treatment for metachromatic leukodystrophy itself. Symptomatic treatments may provide mild relief. Bone marrow tranplants have been performed in a small number of patients.

Support Groups

The United Leukodystrophy Association can be reached at http://www.ulf.org or call 800-728-5483.

Expectations (prognosis)
Metachromatic leukodystrophy is a severely debilitating progressive disease whose outcome is fatal.

Complications

     
  • bronchopneumonia  
  • seizures

Calling your health care provider
Call your health care provider if you have a family history of this disease or if you notice symptoms suggestive of this disorder.

Prevention
Genetic counseling is recommended for parents with a family history of metachromatic leukodystrophy who are planning a pregnancy.

Johns Hopkins patient information

Last revised: December 6, 2012
by Simon D. Mitin, M.D.

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