Population-based genetic screening for reproductive counseling: the Tay-Sachs disease model
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Since 1970, more than 1.4 million individuals worldwide have been screened voluntarily to determine if they are carriers of the mutant gene for Tay-Sachs Disease (TSD). Employing both enzymatic and molecular methods (for optimal sensitivity and specificity) more than 1400 couples have been identified to be at-risk for TSD in their offspring, i.e., both parents heterozygotes. Through prenatal testing of more than 3200 pregnancies, births of over 600 infants with this uniformly fatal neurodegenerative disease have been prevented. In the United States and Canada, the incidence of TSD in the Jewish population has been reduced by more than 90%. More that 100 mutations in the hexosaminidase A gene (the TSD locus) have been identified to date. Some are associated with later onset or more chronic forms of neuronal storage disease. Two mutations cause a carrier-like “pseudo-deficiency” when enzymatic testing is used (false positives). A number of practical, social, and ethical complexities have been identified in this prototypic population-based effort. Educational and counseling components must be provided both before and after screening. Issues of privacy and confidentiality of test results must be addressed. In certain cultures insurability and employment may be involved. The public perception of the biomedical community as advocates for wide-scale testing and screening may be interpreted, in some systems, as conflicts of interest on the part of entrepreneurial scientists, clinicians, and institutions.
Conclusion Many new opportunities for population-based screening will be evident in this era of genome-related discovery. Accordingly, some of the experiences with Tay-Sachs disease prevention may be instructive.