As reported in a recent
commentary in Nature the UK has
decided to allow human trials of mitochondrial replacement. This would involve
a small group of women who have genetic defects in their mitochondria that
could be transmitted to their offspring. The procedure would involve transfer
of only the nucleus of the egg of the affected woman to a healthy enucleated
egg from a donor with subsequent in vitro
fertilization by the male partner. Simply put, it would result in a ‘three
parent baby’ with male and female nuclei provided by the parents and
mitochondrial DNA provided by the donor. The positive aspect is that it would
allow women with mitochondrial defects to have normal children that share most
of their genome. The mitochondrial genes account for only a tiny fraction of
the total genome and thus the children born in this manner would be genetically
very similar to those conceived normally. The aspect of concern is that this
really is re-engineering the human germ line since the mitochondrial DNA could
be passed on indefinitely through female offspring. On an ethical basis there
has been great reluctance to engage in modification of the human germ line, but
this would be a first step.
While the proposed trials
are directed toward preventing offspring with genetic defects one could easily
visualize a ‘slippery slope’ effect here. There is increasing momentum for
using various pharmacological and genetic techniques to enhance human
capabilities (I will be posting much more about this soon). Since mitochondria
can contribute to endurance and athletic performance (1), it will be tempting
to use this relatively simple technology to ‘improve’ one’s offspring with, for
example, mitochondria from an outstanding female athlete. Clearly stringent monitoring will be needed.
1. http://physiolgenomics.physiology.org/content/43/13/789.full
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