Human cloning - can it work?

Dolly the sheep was the first succeccfully cloned mammal. Gradual improvements in cloning technology have enabled researchers to clone mice, cattle, goats, pigs, deer, rabbits, cats, mules, and horses.  Recent successes by South Korean researchers in generating stem cells from cloned human embryos have heightened concerns that human cloning is not impossible.

Even with recent technological advances, animal cloning is still extremely inefficient. For every 100 experiments, only 1, 2, or if lucky, maybe 3 appear to produce a viable offspring in surrogate mothers. While scientific explanations for these failures remain to be defined, many researchers think they represent nothing but technical hurdles that will one day be solved. Even then, its survival beyond the perinatal period is unlikely. These is no reason to believe that any different outcomes will occur if and when human cloning begins.

Scientists believe that the resultant cloning abnormalities are not traceable to the donor nuclei, but it more likely involves failures in genomic reprogramming. Genomic reprogramming in the natural way prior to embryogenesis, involves a stage of development of the egg and the sperm known as gametogenesis, which can take months to years to develop into a mature gamete. This process is sped up during cloning, and it takes only minutes to hours. The process of configuring the exact state of the inner workings of the cell including such complex processes as methylation of the DNA may not be correct for the development of the embryo. Methylation of DNA and other complex functions are now known to be essential to the correct functioning of each human cell, as they ultimately control gene expression. And thus successful cloning may be dependent upon the donated DNA being correctly altered to the state of an early embryo. It is thought by some cloning experts that failure of the nuclear clones to produce viable offspring is due to inappropriate reprogramming of cells, which leads to unregulated gene expression.

It is reasonable to conclude that future human cloning experiments will have the same high failure rates as animal clones. The possibility of performing prenatal genetic screening exists as a way to control quality. If these groups plan on using current routine prenatal diagnosis for the detection of chromosomal and/or other genetic abnormalities, they will not detect the types of epigenetic disturbances that may occur with cloning as there are no extra tools in the developmental pipeline to help improve detection. Research is ongoing to develop reprogramming of certain cells to turn into specific tissues types, which could regenerate nerves, muscles, and other cell types, alleviating Parkinson's, Alzheimer's, and heart disease among other chronic illnesses. There are many potential benefits of therapeutic cell cloning, and this research should not be jeopardized with human cloning activities.

Acknowledgement
http://www.ama-assn.org/ama/pub/physician-resources/medical-science/genetics-molecular-medicine/related-policy-topics/stem-cell-research/human-cloning.page