Terminology used in article on cloning was incorrectBMJ 2001; 323 doi: https://doi.org/10.1136/bmj.323.7316.804a (Published 06 October 2001) Cite this as: BMJ 2001;323:804
- Peter Millard, emeritus professor of geriatrics, St George's Hospital Medical School ()
EDITOR—The myth that stem cells developed by cloning will be genetically similar to the adult needs to be exposed. Scientifically, the statements in the box in Mayor's news article are wrong.1 The Donaldson report (page 23, para 2.28) states “animals born from cell nuclear replacement are not exactly identical to the animal cell whose cell nucleus was used in the process. They inherit mitochondrial DNA (contained in the outer layer of the egg) from the (enucleated) egg used in the nuclear replacement process. The implications of this for the compatibility of tissues derived from embryos created by cell nuclear replacement (cloning) is not known.”2
For this reason, stem cells created by therapeutic cloning cannot be genetically identical because the embryonic stem cells will contain the mitochondrial genes in the cytoplasm of the enucleated female egg. Cloning causes serious biochemical and structural problems in animals.3 Mitochondrial damage would explain the biochemical problems. Four essential biochemical pathways—the citric acid cycle, respiratory chain, oxidative phosphorylation, and fatty acid oxidation—occur in the mitochondrial organelles. Damage to any of these pathways would cause serious biochemical problems.
The age at which mitochondrial illnesses present is affected by intrinsic as well as extrinsic factors.4 Inherited mitochondrial disease can cause blindness, defective muscles (including cardiac muscle), maturity onset diabetes, and deafness. Furthermore, mitochondrial and cell surface receptors mediate the two main pathways of apoptosis.5 And apoptosis has a role in neurodegeneration as well as in cancer.
As far as mitochondrial diseases are concerned, a healthy newborn child does not imply a healthy adult. Many years will have to pass before we can be absolutely certain that techniques currently being used by reproductive scientists for in vitro fertilisation are not causing mitochondrial damage. What is certain, however, is that cloning causes serious biochemical abnormalities in newborn cows.2