Metachromatic Leukodystrophy (MLD): Arylsulfatase A Enzyme Analysis

Clinical Information

Metachromatic leukodystrophy is an autosomal recessive condition caused by a deficiency of arylsulfatase A, an enzyme crucial to the breakdown of sulfatides in the body. The accumulation of sulfatides causes demyelination of nerves. Progressive signs of leukodystrophy include a decline in intellectual abilities and motor skills to the extent that affected individuals lose the ability to walk, speak, see, and hear. This condition can present as late-infantile, juvenile or adult forms, and it is more common in people of Israeli or Navajo descent.

Technical Information

• Arylsulfatase A enzyme activity in leukocytes and fibroblasts are measured using a p-Nitrocatechol sulfate substrate (spectrophotometry).
• Arylsulfatase A enzyme activity in DBS is measured by LC-MS/MS.

Specimen Requirements

• Accepted sample types for this test are dried blood spots, fibroblasts, and leukocytes.
• DBS: Approximately 75 uL of blood should be applied to each of the five circles on filter paper dried blood spot card. Allow blood to dry for at least 4 hours before shipping. If DBS card cannot be shipped immediately, it should be stored at 4 degrees or -20°C prior to shipping to prevent enzyme degradation.
• Fibroblasts: Tissue sample should be stored in sterile culture media; cultured fibroblasts should be sent in two T25 flasks. Do NOT place tissue in formalin or formaldehyde. Do not freeze tissue.
• Leukocytes: A minimum of 5 mL whole blood (7-10 mL preferred) collected in a sodium heparin tube.

Transport Instructions

• DBS: Ship DBS cards at ambient temperature.
• Fibroblasts: Ship tissue sample or cultured fibroblasts at ambient temperature
• Leukocytes: Whole blood should be shipped at ambient temperature. If leukocytes are being isolated at another laboratory, the pellet should be frozen after specimen processing and shipped frozen on dry ice.