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change, what is normal or desirable. Allowing people to do what they want for their progeny will not undermine our humanity.

THERAPEUTIC GENETIC ENGINEERING

Moving beyond prenatal genetic testing and embryo selection, physicians may some day engage in prenatal genetic therapy enabling them to cure genetic disorders by inserting normal or modified genes in sperm or eggs or while a zygote or an embryo is in vitro or a fetus is in the womb. Therapeutic genetic engineering will be used where the far safer and less complicated genetic embryo screening cannot be employed to deal with a range of diseases from the nearly inconsequential to those affecting a person’s quality of life, to the life­threatening— to replace the missing enzyme causing Tay-Sachs or repairing the defective gene otherwise resulting in hemophilia or Huntington’s disease(a degenerative nerve disorder that usually appears between the ages of thirty-five and fifty). We will engage in preventive measures, curing a potential illness or disability in gametes, a fertilized egg, an embryo, or a fetus.

Beyond inherited, clearly defined genetic diseases such as Tay­Sachs, in our genes we carry susceptibility to various other diseases, potentially causing debilitating or deforming illnesses or conditions. Thus, our genes make us at greater risk to certain physical diseases, such as cancer, cardiovascular problems, and arthritis as well as mental disorders, such as depression and schizophrenia. Various kinds of behavior, such as alcohol and drug abuse, may be genetic in origin. With respect to these diseases and behaviors, multiple genes interact in complex, not currently understood, ways. For many illnesses and traits the interaction between genetic and environmental influences is complicated.

In discussing therapeutic genetic engineering, it is helpful to distinguish between somatic and germline intervention. Somatic therapy modifies the nonreproductive cells of a fertilized egg, an