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...