ENHANCEMENT: GENE THERAPY AND SCIENCE FICTION

Scientists are looking to gene therapy as a way to treat medical conditions that have genetic origins. But what if the same gene delivery techniques, once established, could be used to change human traits?

Some people say that gene therapy will open the door to genetic enhancement and the creation of so-called "designer babies." In theory, scientists could someday alter any physical or behavioral trait that is controlled by genes.

In reality, genetic enhancement is not very likely, however. Here's why:

• Finding the right genes to alter: Scientists still know very little about the specific genes that contribute to any given trait. And in fact, most human traits are controlled by multiple genes.
• "Nature versus nurture": No human trait is determined solely by genes. Although genes can contribute to varying degrees, environmental factors - the "who, what, when, where and hows" in life - play a large role in determining how a person develops certain traits. So even if you knew which genes to alter, you could not reliably predict how they would affect the individual.

Most traits are so complex that the concept of enhancement will likely remain in the science fiction realm for the foreseeable future. But if you were dreaming up a plot for your next sci-fi novel, your list might include:

Physical traits, including:

• Appearance, such as hair or eye color
• Height
• Physical build, such as weight or muscle mass
• Strength
• Speed

Behavioral traits, including:

• Intelligence
• Temperament, such as "mellow" or "quick-tempered"
• Personality, such as "shy" or "friendly"

But if you could change human traits, how would you do it?

The details of germline and embryonic gene delivery

Success in gene therapy depends on the efficient delivery of the correct gene to the correct cells in the correct tissue. Once that's accomplished, you still need to make sure the gene gets to work and continues working for the life of the cell. This is not an easy task.

The same can be said for genetic enhancement. If you could use gene delivery techniques to alter a person's traits, you would have to know where and how to deliver the appropriate genes.

Delivering a gene to just one group of cells or one tissue in the body would not change most physical and behavioral traits. To ensure an effect, you would need to deliver the gene to every single cell in the body.

This would be impossible in adults, each of whom is comprised of about 100 trillion cells. (That's 100,000,000,000,000 cells!) The only possible way to alter a gene in every human cell would be to make the change at the earliest stages of development, through germline or embryonic gene delivery:

• Germline gene delivery refers to the permanent transfer of a gene into sperm or egg cells.
• Embryonic gene delivery refers to the permanent transfer of a gene into the cells of an early embryo, just after the sperm and egg unite.

In both cases, the delivered gene would become a permanent part of cells in the resulting adult.

Can you see how germline or embryonic gene delivery might be useful in gene therapy? We've discussed these techniques as methods for genetic enhancement, but scientists are studying them as an approach to treating genetic disorders at the earliest stages of a child's development.

Supported by a Science Education Partnership Award (SEPA) [No. 1 R25 RR16291-01] from the National Center for Research Resources, a component of the National Institutes of Health, Department of Health and Human Services. The contents provided here are solely the responsibility of the authors and do not necessarily represent the official views of NCRR or NIH.