Tuesday, June 3, 2008

Unnatural Selection: Chapter 1

This chapter has the provocative title "Generation of the Upright." For those familiar with Tay-Sachs disease, American Ashkenazim, and recessive genetic diseases in general, this may ring a bell. The Jewish translation, Dor Yeshorim, signifies a genetic testing program implemented by a Rabbi Josef Ekstein; it has wiped out the incidence of Tay-Sachs disease in the communities in which it is followed. Since I have dealt somewhat with various ethical issues written about in the chapter, I will only describe the nature of genetic diseases and the program itself.

Each human has two copies of each gene or a form (allele) thereof, one from each parent. One form (allele) of a given gene may be dominant and, if it is, the other form may be recessive - i.e. it can "hide" or not express itself if a dominant allele of the same gene is present. When a disease is termed "genetic recessive," it only manifests itself if an individual has two copies of the recessive, disease-causing allele. If an individual has one copy of the recessive allele and one copy of the dominant allele, s/he is termed a "carrier" - the disease itself does not show up, but if his or her spouse also has one copy of the recessive allele, their children have a 25% chance of receiving two recessive copies, developing the disease. Tay-Sachs is genetic recessive and kills by age six.

Sometimes it is beneficial to be a carrier of a normally-disease-causing allele because it confers resistance to some other, normally fatal disease. Two examples are Tay-Sachs (of which one copy of the recessive allele protects against tuberculosis epidemics) and sickle-cell anemia (of which a carrier status decreases the individual's susceptibility to malaria).

And what is the program? Since Orthodox Judaism is one of several religions to prohibit abortion, it could not include prenatal testing. Instead, at the age of twelve, all participating Jewish youths are tested via a blood sample to see if they are carriers of the disease. To protect confidentiality, each person is identified at the storage center for blood samples by a six-digit number and the month/day of their birth. When, years later, a young man and woman are considering getting married, they submit their ID numbers and dates to the center; if both are carriers, they are counseled against marriage. If neither or only one is a carrier, they are approved.

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