Therapeutic and Reproductive Cloning

David & Catherine,

There are two types of cloning, therapeutic and reproductive.

The idea behind therapeutic cloning is to generate new cells that perform a function that is missing in the patient, such as cells that produce dopamine in those who suffer from Parkinson's disease or those that produce insulin for those with diabetes.

Cells in the early embryo have nearly all their genes left turned on (unmethylated) which allows them to go on to produce all the structures and functions of the body. As the fetus develops, cells differentiate into cell types with specific functions as the genes for unrelated cell functions are systematically turned off.

Embryotic stem cell research attempts to take these poli-potential cells and coax then into producing specific cell types. Heart muscle cells have been produced in this way. The hope is to mass produce cells that produce dopamine or insulin then introduce them into the patients body where they would migrate to the brain or pancreas, settle in and start producing these missing products.

We know from organ transplants that material from someone else is treated as foreign to the recipient's immune system and may be destroyed if care isn't taken to find compatible donors and the use of immune system suppressants.

This potential rejection can be eliminated in these embryotic stem cell efforts if the stem cells used are created with the patients own dna. A cell from the patient, say a skin cell, can be demethylated through chemical means to return it to its poli-potential state, then introduced onto an egg provided by a donor whose own dna has been removed. The cell is then induced to begin dividing like it would after normal fertilization. The stem cells that result are used to grow the cells that produce the products that are missing in the patient. Since these are clones of the patient's cells, they will not be rejected.

I have no problem with this type of embryotic stem cell research and therapeutic cloning since it is designed to produce only specific cell types in an effort to find relief for specific diseases.

Reproductive cloning is not yet feasible. Gametes which come together during normal fertilization have nearly all their sets of genes turned on. This provides the embryo the potential to produce all the body's structures and functions. The exception to this is that one pattern of genes is turned off (methylated) in the egg and a different pattern of genes is methylated in those in the sperm. When these two gametes with complimentary patterns combine, the likelihood of having a healthy full term baby is increased.

When a skin cell, for example, has to be demethylated to return it to a poly-potential state for potential cloning, this indiscriminate process would remove the male and female methylation patterns as well, resulting in all kinds of potential difficulties in the developing fetus which cannot be ethically tolerated.

The same would apply to same sex procreation. No matter how one tried to produce two gametes, at least one would not have the male or female methylation pattern required for success.

In either case, producing an embryo with the same methylation patterns as occur in the natural fertilization process is way beyond our current understanding or abilities. I would be in favor of a ten year moratorium on human cloning and SS procreation which could be extended after review. If results can be produced that are equivalent in safety and efficacy as IVF, then I see no reason for it to be banned from that point on.

Love, Dad