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Gene therapy in humans has so far been attempted only in somatic cells, where genetic changes introduced in an individual die with that person. By contrast, germline gene therapy (see above) — which would be carried out on newly fertilized human zygotes — would introduce changes not only in every cell of the infant born of such manipulations but also in the genes passed to that baby's progeny. (Some of the scientists at the symposium said, however, that simple methods could keep changes in the recipient from becoming permanent.)

The potential for eliminating disease with such methods is tantalizing. For example, single-base changes in the DNA sequence cause devastating ailments such as Tay-Sachs disease. Such relatively simple targets would be prime candidates for early attempts at germ-line therapy. Complex diseases involving many genes would require much more research and are likely to be targeted farther into the future.

But critics are concerned about the potential for abuse of the technology to ‘enhance’ healthy individuals, by, for instance, manipulating intelligence, emotional stability, longevity or physical appearance. They present the spectre of a booming market in ‘designer’ babies, made to the specifications of parents hungry for success and superiority in their offspring.

Such concern, in part, informed a bioethics convention produced by the Council of Europe last year that has since gathered signatures from 22 European states. This convention says that genetic manipulation may be undertaken for purposes of prevention, diagnosis or therapy — but only if does not aim to introduce a permanent modification in the genome.