Human Growth Hormones

In general, genetic enhancement refers to the exchange of genetic material intended to

modify nonpathological human traits. The term is commonly used to describe efforts optimize

attributes or capabilities by moving an individual from standard to their peak levels of

performance. With enhancement the goal is to modify genes for the desired task needed to be

accomplished. Gene insertion may be intended to affect a single individual through somatic cell

modification, or it may target the gametes, in which case the resulting effect could be passed on

to succeeding generations.

In a sense, the concept of genetic enhancement is not particularly recent if one considers

genetically engineered drug products used to alter physical traits as genetic enhancements. For

example the Human Growth Hormone (HGH), which before 1985 could be obtained only in

limited quantities from cadaveric pituitary glands, now can be produced using recombinant DNA

technology. When its supply was more limited, HGH was prescribed for children with short

stature caused by classical growth hormone deficiency. However, with the advent of recombinant

DNA manufacturing, some physicians have begun recommending use of HGH for hormone

deficient children who are below normal height.

Animal experiments to date have attempted to improve such traits as growth rate or

muscle mass. Although this research is focused on developing approaches to treating human

diseases and conditions, it is possible that discoveries resulting from this research could be

cosmetically applied to enhance traits rather than correct deficiencies.

Similar discoveries could help delay the aging process. For example, a gene called

MGF (Mechano-growth factor) regulates a naturally occurring hormone produced after exercise

that stimulates muscle production. Levels of MGF fall as we age, which the is reason why

muscle mass is lost as we grow older. A treatment to build up muscles would allow us to remain

able-bodied and independent much longer. IGF-1, another muscle-building hormone, has

produced increased muscle mass in laboratory mice. Theoretically, gene insertion of IGF-1 could

produce an equally impressive effect in humans.

Efforts to genetically improve the growth of swine have involved the insertion of

transgenes encoding growth hormone. Nevertheless, despite the fact that growth hormone

transgenes are expressed well in swine, increased growth does not occur. Another effort aimed to

enhance muscle mass in cattle. When gene transfer was accomplished, the transgenic calf

initially exhibited muscle hypertrophy, but muscle degeneration and wasting soon followed and

the animal had to be destroyed.

Gene transfer at the embryonic stage through a technique called pronuclear

microinjection is another approach being tested in animals. However, current knowledge from

animal experiments suggests that embryo gene transfer is unsafe, as its use results in random

integration of donor DNA, a lack of control of the number of gene copies inserted, significant

rearrangements of host genetic material, and a 5 to 10 percent frequency of insertional

mutagenesis. In addition, this technique would necessarily be followed by nuclear transfer into

enucleated oocytes, a process that in at least two animal models is associated with a low birth

rate and a very high rate of late pregnancy loss or newborn death. This is why many believe that

the use of gene transfer at the embryonic stage for enhancement would reach far beyond the

limits of acceptable medical intervention.

Greater success has been achieved in genetic enhancement of plants, which are more

easily manipulated genetically and reproductively. However, the state of knowledge in humans

and other complex organisms does not allow for the controlled genetic modification of even

simple phenotypes.

For example, in humans, for whom more complex traits such as intelligence or behavior

are concerned, the limitations are more pronounced. The genome provides only a blueprint for

formation of the brain. The complex and subtle details of assembly and intellectual development

involve more than direct genetic control and are subject to inestimable environmental influences.

Despite the technical limitations, it is possible that eventually enhancements using techniques

initially intended to restore deficiencies could be redirected to improve memory and problem-

solving, reduce the need for sleep, increase musical capacity, attain desirable personality traits,

protect against cardiovascular disease or cancer, or increase longevity.

Ethical issues

Genetic enhancement raises a host of ethical, legal and social questions. What is meant

by normal? When is a genetic intervention "enhancing" or "therapeutic?" How should the benefit

from a genetic enhancement be calculated