Test Id : ARSAB

For information see Lysosomal Disorders Diagnostic Algorithm, Part 2.

This test primarily serves as a second-tier assay to be used by newborn screening programs to screen for metachromatic leukodystrophy when first tier sulfatide analysis is abnormal. The test can also be used to screen patients at risk for metachromatic leukodystrophy.

Supplies: Card-Blood Spot Collection (Filter Paper) (T493)

Container/Tube:

Preferred: Card-Blood Spot Collection (Filter Paper)

Acceptable: PerkinElmer 226 filter paper, Munktell filter paper, Whatman protein Saver 903 paper, local newborn screening card, or blood collected in tubes containing EDTA (preferred) or heparin and dried on filter paper

Specimen Volume: 2 Blood spots

Collection Instructions:

1. Completely fill at least 2 circles on the filter paper card (approximately 100 microliters blood per circle).

2. Let blood dry on filter paper at ambient temperature in a horizontal position for a minimum of 3 hours.

3. Do not expose specimen to heat or direct sunlight.

4. Do not stack wet specimens.

5. Keep specimen dry and freeze (with desiccant if necessary).

Additional Information:

1. For collection instructions, see Blood Spot Collection Instructions

2. For collection instructions in Spanish, see Blood Spot Collection Card-Spanish Instructions (T777)

3. For collection instructions in Chinese, see Blood Spot Collection Card-Chinese Instructions (T800)

• Biochemical Genetics Patient Information
• Blood Spot Collection Card-Spanish Instructions
• Blood Spot Collection Card-Chinese Instructions
• Blood Spot Collection Instructions

Biochemical Genetics Patient Information (T602)

1 Blood spot

Enzymatic test for detection of arylsulfatase A deficiency

This test is not suitable for carrier detection.

Metachromatic leukodystrophy is caused by deficient activity of arylsulfatase A (ARSA) enzyme and is characterized by progressive neurologic changes and leukodystrophy with variable age of onset.

Pseudodeficiency of ARSA enzyme has been recognized among patients with other unrelated neurologic conditions as well as among the general population.

Additional studies, such as molecular genetic testing of ARSA (CGPH / Custom Gene Panel, Hereditary, Next-Generation Sequencing, Varies; specify ARSA Gene List ID: IEMCP-WHFH2K), urinary excretion of sulfatides (CTSU / Ceramide Trihexosides and Sulfatides, Random, Urine), and, if necessary, histological analysis for metachromatic lipid deposits in nervous system tissue are recommended to confirm a diagnosis.

For information see Lysosomal Disorders Diagnostic Algorithm, Part 2.

Metachromatic leukodystrophy (MLD) is a lysosomal disorder caused by a deficiency of the enzyme arylsulfatase A (ARSA), which leads to the accumulation of sulfatides (both galactosyl and lactosyl sulfatide) in the white matter of the central nervous system, the peripheral nervous system, and, to a lesser extent, in visceral organs including the kidney and gallbladder. Cells that produce myelin are especially affected causing the characteristic leukodystrophy seen in MLD. Patients with MLD excrete excessive amounts of sulfatides in their urine.

The 3 clinical forms of MLD are late-infantile, juvenile, and adult, depending on age of onset. All forms result in progressive neurologic changes and leukodystrophy demonstrated on magnetic resonance imaging. To date, late-infantile MLD is most commonly diagnosed (50%-60% of cases) and usually presents before 30 months of age with hypotonia, clumsiness, diminished reflexes, and dysarthric speech. Progressive neurodegeneration occurs and, unless successfully treated, most patients do not survive past childhood. Juvenile MLD (20%-30% of cases) is characterized by onset between 30 months to 16 years old. Presenting features are behavior problems, declining school performance, clumsiness, and slurred speech. Neurodegeneration occurs at a somewhat slower and more variable rate than the late-infantile form. Adult MLD (15%-20% of cases) has an onset after puberty and can be as late as the fourth or fifth decade. Presenting features are often behavior and personality changes, including psychiatric symptoms. Clumsiness, neurologic symptoms, and seizures are also common. The disease course has variable progression and may occur over 2 to 3 decades.

Metachromatic leukodystrophy is an autosomal recessive disorder caused by disease-causing variants in the ARSA gene. This disorder is distinct from conditions caused by deficiencies of arylsulfatase B (Maroteaux-Lamy disease) and arylsulfatase C (steroid sulfatase deficiency). Saposin B deficiency is a rare autosomal recessive disorder with symptoms that mimic MLD; however, ARSA activity is not deficient. Like MLD, patients with saposin B deficiency can excrete excessive amounts of sulfatides in their urine. Individuals with multiple sulfatase deficiency, which is clinically distinct from MLD, will also have deficiency of ARSA, however, other sulfatase enzymes will also be deficient.

Individuals with "pseudodeficiency" of ARSA have very low levels of ARSA activity but are otherwise healthy. Pseudodeficiency has been found among patients with other unrelated neurologic conditions as well as among the general population, therefore a diagnosis of MLD cannot be based upon reduced ARSA activity alone. To confirm a diagnosis, additional studies, such as molecular genetic testing of ARSA (CGPH / Custom Gene Panel, Hereditary, Next-Generation Sequencing, Varies; specify Gene List ID: IEMCP-WHFH2K), urinary excretion of sulfatides (CTSU / Ceramide Trihexosides and Sulfatides, Random, Urine), and/or histological analysis for metachromatic lipid deposits in nervous system tissue are recommended. While sulfatides appear to be elevated in newborn dried blood spots and is used as a primary newborn screening test, the utility of sulfatide analysis in dried blood spots outside of newborn screening has not been determined.

Current treatment options for MLD depend on the clinical stage and presence of neurologic symptoms. Early diagnosis is extremely important to improve clinical outcomes. Allogenic hematopoietic stem cell transplant can treat symptoms related to the central nervous system in pre- and very early-symptomatic juvenile- or adult-onset MLD. Recently, autologous hematopoietic stem cell-based gene therapy has been approved in the U.S. and elsewhere for individuals with presymptomatic late-infantile MLD, presymptomatic juvenile MLD, or early-symptomatic juvenile MLD with maintained ability to walk and before the onset of cognitive decline.

Normal: > or =0.100 mmol/mL/hr

Reduced levels of arylsulfatase A (ARSA) are seen in patients with metachromatic leukodystrophy (MLD), however some patients with MLD may have normal results by this method.

Individuals with pseudodeficiency of ARSA can have results in the affected range but are otherwise unaffected with MLD.

Reduced levels of ARSA are also possible when samples have been left at room temperature after drying.

Abnormal results and/or clinical suspicion should be confirmed using CTSU / Ceramide Trihexosides and Sulfatides, Random, Urine and molecular genetic testing of ARSA (CGPH / Custom Gene Panel, Hereditary, Next-Generation Sequencing, Varies; specify Gene List ID: IEMCP-WHFH2K).

This test is not reliable in identifying carriers.

Arylsulfatase A (ARSA) is also deficient in individuals with multiple sulfatase deficiency and possibly in saposin B deficiency.

Specimens not immediately refrigerated or frozen after drying may yield falsely low ARSA activity results.

This disorder is distinct from conditions caused by deficiencies of arylsulfatase B (Maroteaux-Lamy disease) and arylsulfatase C (steroid sulfatase deficiency).

1. Gomez-Ospina N. Arylsulfatase A deficiency. In: Adam MP, Feldman J, Mirzaa GM, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 1993-2025. Updated April 25, 2024. Accessed June 4, 2025. Available from: www.ncbi.nlm.nih.gov/books/NBK1130/

2. Fumagalli F, Calbi V, Natali Sora MG, et al. Lentiviral haematopoietic stem-cell gene therapy for early-onset metachromatic leukodystrophy: long-term results from a non-randomised, open-label, phase 1/2 trial and expanded access. Lancet. 2022;399(10322):372-383. doi:10.1016/S0140-6736(21)02017-1

3. Fumagalli F, Zambon AA, Rancoita PMV, et al. Metachromatic leukodystrophy: A single-center longitudinal study of 45 patients. J Inherit Metab Dis. 2021;44(5):1151-1164. doi:10.1002/jimd.12388

4. Laugwitz L, Mechtler TP, Janzen N, et al. Newborn screening and presymptomatic treatment of metachromatic leukodystrophy. N Engl J Med. 2024;391(13):1256-1258. doi:10.1056/NEJMc2407165

A 3 mm sample is excised from a dried blood spot (DBS) specimen. Arylsulfatase A is isolated from the DBS aliquot by mixing with extraction reagent on a rotating incubator. The enzyme is then purified from the matrix using size exclusion chromatography. The sample is then incubated in the presence of internal standard, substrate, and assay buffer. Next, salts are removed using liquid/liquid extraction. A final purification step using solid phase extraction is performed before the dried down and reconstituted specimen is analyzed by flow injection tandem mass spectrometry.(Unpublished Mayo method)

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This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

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