A simple chromogenic assay for arylsulfatase A

Area of Science:

• Biochemistry
• Enzymology
• Clinical Diagnostics

Background:

• Arylsulfatase A (ARSA) deficiency causes Metachromatic Leukodystrophy (MLD).
• Accurate measurement of residual ARSA activity is crucial for diagnosing MLD and pseudodeficiency.
• Existing assays may lack sensitivity for detecting low ARSA levels.

Purpose of the Study:

• To develop a simple and accurate assay for determining low residual arylsulfatase A activity.
• To differentiate between MLD patients and pseudodeficiency individuals using residual ARSA activity.
• To quantify ARSA activity in cultured skin fibroblasts from MLD patients and controls.

Main Methods:

• Utilized the differential activity of arylsulfatase A and B at 0°C and 37°C.
• Employed 4-nitrocatechol-sulfate as a chromogenic substrate.
• Assayed residual ARSA activity in cultured skin fibroblasts.

Main Results:

• Arylsulfatase A activity was 24% at 0°C compared to 37°C, while arylsulfatase B was nearly inactive at 0°C.
• Residual ARSA activities in late-infantile MLD patients were 0.0%, juvenile patients 1.0%, and adult patients 4.4-14%.
• Healthy pseudodeficient individuals showed residual ARSA activity between 18% and 32%.

Conclusions:

• The developed assay accurately quantifies low residual arylsulfatase A activity.
• This assay effectively distinguishes MLD patients from pseudodeficiency individuals.
• The findings support the use of this assay for diagnosing MLD subtypes.