Clinical Utility

Metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive inherited disorder in which the desulfation of 3-0-sulfogalactosyl-containing glycolipids by arylsulfatase A (ASA) is defective. The clinical onset and severity of MLD is variable. The late infantile form typically presents in the second year of life, the juvenile form presents between age 4 and puberty, and the adult form may present at any age after puberty. Gait disturbance and mental regression are the earliest signs. Depending on the variant, other symptoms include blindness, seizures, and behavioral disturbances. Diagnosis of MLD is complicated by the fact that significant reduction of ASA activity may not prove MLD and that its presence does not exclude it. Significant reduction of ASA activity is observed in individuals homozygous for the pseudodeficiency allele. Normal ASA activity is observed in MLD patients with a deficiency of saposin B. Residual activity  can be detected in patients with late infantile MLD. Arylsulfatase B should always be measured if ASA is deficient.

Multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is a rare autosomal recessive disorder characterized by the deficiencies of all 12 known sulfatases and leading to a clinical presentation that generally resembles late infantile MLD. Biochemical confirmation is made by reduced activity of both arylsulfatase A and B.