530 GENE FREQUENCIES FOR TAY-SACHS (TSD) AND SANDHOFF'S DIS-530 EASE (SD) IN JEWISH AND NONJEWISH POPULATIONS

Abstract

Since 1974, 40,012 individuals have volunteered for TSD heterozygote screening in Ca.. Of these, 6,795 are “nonJewish”. With an automated serum hexosaminidase (HEX) assay, a tri-variable analysis is possible: Total HEX activity (TA) ; % HEX A (56°); and nanomoles HEX A (nM): TA × %A. Genotype assignment is based on:

Suspect SD carriers (serum TA < 450; %A > 75) and TSD heterozygotes (%A < 50; nM A <420) are confirmed by WBC testing and family studies. The SD gene has been identified in 20 families in this way (4 Jewish). In Jews the gene frequency for TSD is 0.0167 (1:30 carriers) and for SD is 6.0 × 10⁻⁵ (1:8304 carriers). In “nonJews” the TSD gene frequency is 0.0035 (1:141 carriers) and for SD, 0.0012 (1:425 carriers).

These data provide the first direct approximations of the gene frequencies for TSD and SD in the Jewish and nonJewish populations. Because of possible nonrandomness in the sample and ancestral uncertainties, these figures should be viewed as reasonable estimates only. Similar analyses with sera from obligate heterozygotes for I-Cell Disease and Mucolipidosis III may allow carrier frequency estimates for these recessive alleles in these populations as well.

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