Background: Maternal spindle transfer (MST)

How would maternal spindle transfer be done? 

  • First, assisted reproduction techniques are used to allow the extraction of the intending mother’s egg from her ovaries. The cytoplasm of her egg contains mutated (unhealthy) mitochondria.

  • Chromosomes (nuclear DNA material) in the mother’s egg are found in a group which looks ‘spindle shaped’. This is removed for transfer to the donor egg. The mother’s chromosome-free egg containing the unhealthy mitochondria is then discarded.

  • At the same time, a donated egg is taken from an unrelated woman who has healthy mitochondria.

  • The chromosomes of the donor’s egg are removed and discarded, leaving behind her healthy mitochondria in the cytoplasm.

  • The ‘spindle’ of chromosomes taken from the mother’s egg is now placed into the enucleated donor egg.

  • The resulting reconstructed egg contains nuclear DNA from the mother, and healthy mitochondria from the donor.

  • This egg can then be fertilised with sperm from the intending father, and the resulting embryo transferred back to the intending mother. This will enable her to carry a pregnancy that will be unaffected by inherited mitochondrial disorders.

About maternal spindle transfer

Scientific developments

Maternal spindle transfer is a similar technique to pronuclear transfer, the main difference being that it uses unfertilised eggs instead of early embryos.

In 2009, researchers in Oregon announced they had successfully used maternal spindle transfer in rhesus macaques.1  They found the primate eggs capable of supporting normal fertilisation, and went on to have normal embryo development. Three healthy offspring were produced. No mutated mitochondria from the affected egg were detected in the three monkeys born. Their growth is monitored monthly and, thus far, at the current age of over two years, no difference has been noted between the experimental macaques born following maternal spindle transfer and controls.

In collaboration with the researchers from Oregon, researchers at Newcastle University are currently testing the maternal spindle transfer technique on human eggs, the results of which have yet to be published.

Legal and policy developments

The same legal and regulatory constraints currently apply to the maternal spindle transfer technique in the HFE Act 2008, as to the pronuclear transfer technique. Similarly, maternal spindle transfer would be permitted for use in treatment only if Parliament agrees that the meaning of ‘permitted eggs’ for treatment should be extended to include ‘eggs...that have been treated in such a way as specified in regulations to prevent the transmission of serious mitochondrial disease’.

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1 Tachibana M, Sparman M, Sritanaudomchai H et al. (2009) Mitochondrial gene replacement in primate offspring and embryonic stem cells Nature 461: 367-72.