Editorials

Nuclear transfer to prevent maternal transmission of mitochondrial DNA disease

BMJ 2012; 345 doi: http://dx.doi.org/10.1136/bmj.e6651 (Published 03 October 2012) Cite this as: BMJ 2012;345:e6651
  1. Joanna Poulton, professor of mitochondrial genetics1,
  2. Pippa Oakeshott, reader in general practice2
  1. 1University of Oxford, Nuffield Department of Obstetrics and Gynaecology, Women’s Centre, Oxford OX3 9DU, UK
  2. 2Community Health Sciences, St George’s, University of London, London, UK
  1. joanna.poulton{at}obs-gyn.ox.ac.uk

Would be a major advance, but safe alternatives exist for most affected families

Two new techniques to prevent diseases of maternally transmitted mitochondrial DNA—maternal spindle transfer and pronuclear transfer—have prompted a public consultation by the Human Fertilisation and Embryology Authority (HFEA) in the United Kingdom.1 2 3 After the announcement of the consultation, much of the comment in the press focused on “three parent embryos” as if they were a novelty.4 They are not, and such red herrings serve only to cloud the debate.

About one in 400 people have a maternally inherited pathogenic mutation of mitochondrial DNA. Mutations may cause no symptoms or may present at any age with problems such as developmental regression, deafness, blindness, neuropathy, diabetes, or cardiomyopathy. Mitochondrial DNA is maternally inherited because mitochondria are located in the cytoplasm, and the sperm contributes almost no cytoplasm to the fertilised egg. Many of these diseases are heteroplasmic—that is, mitochondria with mutant and normal DNA coexist in the same patient; low doses of mutant DNA cause mild symptoms and high doses cause severe symptoms. If heteroplasmic women transmit high doses of mutant mitochondrial DNA to their children,5 these children are severely affected. Homoplasmic women, whose mitochondria all have identical DNA, transmit 100% mutant …

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