Human Cloning the Debate Over Human Cloning

Human Cloning

The debate over human cloning generally assumes it's possible to safely clone a completely normal human being, and ignores the multitude of problems that routinely plague the process of cloning animals. The current definition of 'successful cloning' is the generation of a viable adult organism (Gurdon and Melton, 1811), a definition used rather loosely given the prevalence of defects that occur. As discussed below, this definition has been traditionally applied to the cloning of domesticated animals and is not adequate for defining success should human cloning ever be attempted.

Somatic Cell Nuclear Transfer

The number of mammals that have been successfully cloned from somatic cells has increased steadily since the first sheep, Dolly, was cloned in 1996 (reviewed by Campbell et al., 257). These include mouse, rat, cow, goat, pig, rabbit, cat, dog, mule, horse, and deer. The process of cloning involves the transfer of a unit of complete genetic material (somatic cell nucleus) from a cell taken from an adult animal, into an ovum or egg that has had its nucleus removed (Campbell et al., 256). The intended result is the creation of a genetically identical organism. The reason this is possible is because an ovum contains enzymes that rapidly and efficiently 'reprogram' the inserted genetic material to a more immature, stem cell-like state. The reprogramming is necessary before the ovum is capable of producing all the different types of cells required to make a viable adult mammal from a single cell. What most laypeople fail to realize, is that this process is immensely complex and prone to failure on a number of levels because the reprogramming tends to be non-specific and incomplete (Gurdon and Melton, 1812).

The average success rate of generating a single adult animal from somatic cell nuclear transfers is about 1-2% (Gurdon and Melton, 1811). In other words, an average of 50 to 100 eggs would have to be expended before a successful cloning event occurred. How many women would be willing to subject themselves to in vitro fertilization protocols to support a somatic cell nuclear transfer pregnancy, when the chance of success is between 1-2% (Gurdon and Melton, 1811)? The prevalence of first trimester miscarriages in cattle and sheep is between 50 and 70% (Palmieri et al., 865). Many of these failures result from the embryo failing to properly support placental development, and recent research has revealed that somatic cell nuclear transfer embryos and placenta have abnormal gene expression patterns (Campbell et al., 257). Many of the embryos that do reach term suffer from Large Offspring Syndrome, immature lungs, generalized weakness, immunodeficiencies, and high mortality rates. These defects are believed to result from disruptions in genomic imprinting, which is a biological mechanism that controls inherited patterns of gene expression essential for proper growth, development, and viability (Butler, 478).

Summary

The current state of cloning technology assures the success rate of any human cloning efforts would be dismal and fraught with countless miscarriages, birth abnormalities, and perinatal deaths. Unless we're willing to approach human reproduction in the same manner that we treat livestock reproduction, it seems unlikely that rational minds would be willing to consider human cloning as a viable medical procedure. This state of affairs provides a little breathing room so that the ethical and legal issues surrounding human cloning can be more fully addressed.