Interpretation of Test Results

A pseudodeficiency allele, R247W, is present in approximately 2% of Ashkenazi Jewish individuals who are carriers by the enzymatic assay. The R247W variant decreases the activity of HEX A for the artificial substrate used in the laboratory but does not cause TSD since it does not affect HEX A activity for its natural substrate, GM2 ganglioside.

About 36% of non-Jewish individuals who are carriers by enzyme analysis have a pseudodeficiency allele (32% R247W and 4% R249W). In addition, screening for the three common Ashkenazi Jewish mutations and an additional mutation (IVS9+1G^ A) will identify approximately 95% of Ashkenazi Jewish carriers, but only 40% to 50% of disease-causing alleles in non-Jews. Other populations who are at high risk, such as the French Canadians, Cajuns, and Pennsylvania Dutch, have their own common alleles. Therefore, the mutations included for population screening must target the specific mutations of the ethnic background of the individual being tested.

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