DNA-BASED DIAGNOSIS OF ARYLSULFATASE A DEFICIENCIES AS A SUPPLEMENT TO ENZYME ASSAY - A CASE IN POINT

Objective: To identify the molecular basis of arylsulfatase A deficien cy in a family at risk for metachromatic leukodystrophy (MLD) and dete rmine the genetic risk in the offspring. Methods: Mutations in the ary lsulfatase A gene were identified by PCR amplification and restriction enzyme digestion. Individuals had previously been tested for arylsulf atase A activity. Results: Assays of arylsulfatase A activity had resu lted in ambiguous results for MLD carrier identification. DNA analysis clearly identified two MLD mutations in the family, and an unsuspecte d arylsulfatase A pseudodeficiency. The DNA information immediately cl arified the MLD risk for the family and confirmed that a newborn with low arylsulfatase A activity was unaffected. Conclusions: The overlap between activities for various combinations of MLD and pseudodeficienc y alleles and the variability inherent in the assay of arylsulfatase A complicate the interpretation of activity levels in families at risk for MLD. Use of simple molecular biological tests for pseudodeficiency and the common MLD mutations in combination with the enzyme data can facilitate carrier identification and prenatal diagnosis.