Human gene therapy: scientific and ethical considerations.

The term "gene therapy" encompasses at least four types of application of genetic engineering for the insertion of genes into humans. The scientific requirements and the ethical issues associated with each type are discussed. Somatic cell gene therapy is technically the simplest and ethically the least controversial. The first clinical trials will probably be undertaken within the next year. Germ line gene therapy will require major advances in our present knowledge and it raises ethical issues that are now being debated. In order to provide guidelines for determining when germ line gene therapy would be ethical, the author presents three criteria which should be satisfied prior to the time that a clinical protocol is attempted in humans. Enhancement genetic engineering presents significant, and troubling, ethical concerns. Except where this type of therapy can be justified on the grounds of preventive medicine, enhancement engineering should not be performed. The fourth type, eugenic genetic engineering, is impossible at present and will probably remain so for the foreseeable future, despite the widespread media attention it has received. There are four potential levels of the application of genetic engineering for the insertion of gene into a human being. Somatic cell therapy: this would result in correcting a genetic defect in the somatic (i.e.,body) cells of a patient. Germ line gene therapy: this would require the insertion of the gene into the reproductive tissue of the patient in such a way that the disorder in his or her offspring would also be corrected. Enhancement genetic engineering: this would involve the insertion of a gene to try to "enhance" a known characteristic; for example, the placing of an additional growth hormone gene into a normal child. Eugenic genetic engineering: this is defined as the attempt to alter or "improve" complex human traits each of which is coded by a large number of genes; for example, personality, intelligence, character, formation of body organs, and so on.