The Disease in the Future

There has been some debate on whether or not the incidence of TSD is increasing. R. F. Shaw and A. P. Smith (1969) argue that it is, basing their conclusion on a calculation that assumes a heterozygote advantage of approximately 5.3 percent, a value slightly higher than that calculated by Myrianthopoulos and Aronson (1966). On the other hand, Myrianthopoulos, A. F. Taylor, and Aronson (1970) doubt that the TSD gene is increasing because the conditions (high prevalences of tuberculosis) that may have offered the heterozygote an advantage in the past are no longer present. Chase and McKusick (1972) suggest that the present high incidence of TSD is "a transient phenomenon due to the chance encounter of recessive genes whose frequency has reached a high level partly as a consequence of diminished inbreeding." It must also be kept in mind, though, that present-day high levels of TSD may be an artifact of better diagnosis and case reporting.

Aside from the continuing study and debate about the different aspects of TSD touched on here, there are some more immediate concerns. At the present time, there is no cure for TSD. However, because heterozygote carriers of a TSD gene can be identified by a clinical test, as can an affected fetus through amniocentesis, individuals have available to them some important options. M. M. Kaback and R. S. Zeiger (1972) conducted the first major effort to identify TSD heterozygote carriers. Kolodny (1979) gives three reasons for the success of this screening program:

1. The testing program was targeted toward a defined subgroup of the population, namely, Ashke-nazi Jews in their childbearing years.

2. A relatively simple, accurate, and inexpensive method was available for determining heterozygote status in an individual.

3. An in utero test for Tay-Sachs disease existed.

Kolodny (1979) went on to note that as a result of this and other screening programs more than 100 TSD births had been averted. Kaback and colleagues (see his 1979, 1981) present detailed information and updates on various aspects of TSD

screening programs. D. A. Greenberg and Kaback (1982) report that at the time of their writing, over 200,000 adults in the United States had been screened for TSD carrier status. Estimates of TSD carrier frequencies vary somewhat from one study to another. O'Brien (1983) predicts a U.S. Ashkenazi Jewish population carrier frequency of 2.6 percent, whereas Kolodny (1979) estimates the frequency to be 3.7 percent.

Bradford Towne

I would like to thank Dr. Jean W. MacCluer for her comments and suggestions on this article.

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