Tay-Sachs disease (TSD) is an autosomal recessive
genetic disorder resulting from mutation of the HEXA gene encoding the alpha-subunit of the lysosomal
enzyme,
beta-N-acetylhexosaminidase A (
Hex A). We have discovered that a Tay-Sachs mutation, IVS-9 + 1 G-->A, first detected by Akli et al. (Genomics 11:124-134, 1991), is a common disease allele in non-Jewish Caucasians (10/58 alleles examined). A PCR-based diagnostic test, which detects an NlaIII site generated by the mutation, revealed a frequency among
enzyme-defined carriers of 9/64 (14%). Most of those carrying the allele trace their origins to the United Kingdom, Ireland, or Western Europe. It was not identified among 12 Black American TSD alleles or in any of 18 Ashkenazi Jewish,
enzyme-defined carriers who did not carry any of the mutations common to this population. No normally spliced
RNA was detected in PCR products generated from reverse transcription of
RNA carrying the IVS-9 mutation. Instead, the low levels of
mRNA from this allele were comprised of aberrant species resulting from the use of either of two cryptic donor sites, one truncating exon 9 and the other within IVS-9, spliced to exon 10. Numerous additional splice products were detected, most involving skipping of one or more surrounding exons. Together with a recently identified allele responsible for
Hex A pseudodeficiency (Triggs-Raine et al. Am J Hum Genet, 1992), these two alleles accounted for almost 50% (29/64) of TSD or carrier alleles ascertained by
enzyme screening tests in non-Jewish Caucasians.