Three into two won’t go

The very idea that one might conceive a child using the DNA from three parents is one that makes us shudder. But let’s check our immediate instincts and think the problem through. The announcement today about the transfer of DNA from one egg to another in order to avoid the damage caused by faulty mitochondria will be the source of much discussion. Those of you who want to look behind the headlines might first try the good lay account at Nature News.

In order to review the Church’s principles you may want to look at Donum Vitae, a CDF document.

You will notice that, although the eggs used are fertilised, the fusing of the maternal and paternal DNA, and therefore conception, has not taken place. But there are plenty of other issues to consider: artificial fertilisation, the ethical and social questions arising from three sources of DNA, and our rights to tamper with the natural process of conception.  And this is all to be weighed against the potential benefits for which the procedure was developed. It is not an issue on which I would care to give a snap answer. But you may well have some thoughts to share with us.

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About Quentin

Science Editor, Catholic Herald. Portrait © Jacqueline Alma
This entry was posted in Bio-ethics, Moral judgment. Bookmark the permalink.

8 Responses to Three into two won’t go

  1. Ion Zone says:

    I dunno, it’s not like killing an embryo for cancerous stem cells. It would be very strange for the child, and unnatural, but they might enjoy a far greater life as a result.

  2. Vincent says:

    The difficult issue here, as I understand it, is that the creation of a new life – that is a human being called by God to live with him for ever in heaven comes about through a biological act. Not surprisingly Donum Vitae, to which Quentin directs us, emphasises the sacredness of the whole process. It must be a fully human act which is the expression of love between a married couple, and it can by no means be treated as a normal biological event – with which we are entitled to interfere even for good motive.
    If the scientists are successful in helping a child to be conceived without the malformation of faulty mitchondria, our immediate instinct is to cheer. But the benefit may be a short term one, and open the way to an acceptance that we are free to do anything we wish with the process of procreation. Imagine the possibility of producing new human beings from, say, skin cells, which have been reprogrammed. Or perhaps producing a hybrid from mating human DNA with animal DNA. Such procedures may look both grotesque and unlikely today. But they are no more grotesque and unlikely than this current procedure would have looked a few years back.
    It is quite clear that civil authority, although it may delay some procedures, cannot be relied upon to control the situation.And people who are refused a procedure in one country can always find another country which would be willing.
    I think this is a very important test case. Our natural instincts cannot be decisive here.

  3. Horace says:

    We have visited this question before; see:- “Two mothers but one baby” in STOP PRESS May 2008.
    I have looked very carefully at Donum Vitae and I think that, provided the maternal and adjuvant eggs had NOT been fertilised, then if the exchange of mitochondria was carried out and the repaired egg returned to the original mother’s womb so that fertilisation could occur in the natural way then the whole procedure might be considered licit.
    Thus:-
    “A strictly therapeutic intervention whose explicit objective is the healing of various maladies such as those stemming from chromosomal defects will, in principle, be considered desirable, provided it is directed to the true promotion of the personal well-being of the individual without doing harm to his integrity or worsening his conditions of life. Such an intervention would indeed fall within the logic of the Christian moral tradition”

  4. Horace, you may be able to provide further clarification. As I understand it, the egg is fertilised but the fusing of the parental DNA has not taken place – thus a human being with its unique DNA blueprint is not present. Or is this a distinction without a difference?
    It may be worth mentioning that mitochondria does carry its own DNA (mtDNA). Although the amount by comparison is small, its effects can be large. I believe that the new techniques were used as a way of minimising this, but are not always completely successful.

  5. Horace says:

    I am not by any means an expert but this is how I think it works:-
    1) The egg is enclosed in a membrane and as a sperm makes its way through this membrane a reaction occurs which changes the enclosing membrane in a way which stops any other sperm getting through (OK there may be a tie but this doesn’t happen very often)
    2) Both the nucleus of the egg and the nucleus of the sperm then undergo changes which result in the formation of ‘pronuclei’ each containing only half the normal complement of chromosomes. At this stage the male mitochondria degenerate and are lost but the female mitochondria persist outside the pronucleus.
    3) The pronuclei are subsequently drawn together and fuse so that the resulting nucleus has the full number of chromosomes (half from the female the other half from the male).

    This last stage is what I think is properly referred to as ‘fertilisation’.
    However it is also possible to refer to the whole procedure as ‘fertilisation’.

    The description in Nature News suggests that the extraction of a nucleus and its replacement with a different nucleus actually refers to pronuclei and requires both eggs to be in stage (2). If this is so then I would think it very difficult, but perhaps not impossible, to carry out the procedure in such a way as to fulfill the conditions for a licit procedure as described in Donum Vitae – since fertilisation proper only occurs in stage (3).

    If, on the other hand, the exchange of nuclei – separate from mitochondria – could be effected before the egg encountered a sperm then (as there is no question of interfering with an existing living being) the morality of the procedure should not be significantly different from that of e.g. a kidney transplant.

  6. That’s all clear now. Thanks. But there’s just a point at your stage 3. If the cells being used for the process are still at the pronucleus stage then the process of combining the male and female DNA has not yet taken place. If that is so, then the unique pattern which actually lies behind each human being is not yet formed.

    This is Wiki’s definition of pronucleus:
    “A pronucleus (plural: pronuclei) is the nucleus of a sperm or an egg cell during the process of fertilization, after the sperm enters the ovum, but before they fuse. Sperm and egg cells are haploid, meaning they carry half the number of chromosomes. When the pronucleus of a sperm fuses with the pronucleus of an egg, their chromosomes combine and become part of a single diploid nucleus in the resulting embryo, containing a full set of chromosomes. The appearance of two pronuclei is the first sign of successful fertilization as observed during in vitro fertilisation, and is usually observed 18 hours after insemination or ICSI.“

    All this would suggest that the new (still very experimental) procedure is not an interference with an embryo, but a pre-embryo. I don’t suggest that there aren’t other moral problems in this issue but they do not seem to me to appear at this point.

    Am I on the right lines?

  7. Horace says:

    Quentin: Yes. I agree.
    As you say the exchange of nuclei is not an interference with an embryo, but a pre-embryo.
    The moral difficulty arises because in the procedure as described a sperm is already involved. Question is; how did it get there? It is difficult to see how it could get there except during the procedure of artificial insemination and we are told ” By acting in this way the researcher usurps the place of God . . “.
    I do not know if it might be possible to use “unfertilised” eggs and swap nuclei leaving mitochondria in situ (although I can’t see any obvious reason why it shouldn’t). As I said, if this were possible then many of the moral worries might disappear.

  8. RMBlaber says:

    What the Newcastle University team have done is taken an ovum donated by Woman A, and stripped it of its nucleus, so that it no longer has any of its own nuclear DNA, but _does_ still have its mitochondria (and thus mitochondrial DNA).

    Next, they have taken the nucleus from an ovum donated by Woman B and placed it in Woman A’s denucleated ovum; and finally, they have fertilised the resulting egg with sperm from Woman B’s husband.

    The intention has, as has been stated, to avert the severe (and ultimately fatal) disabilities caused to the child by the inheritance of its mother’s defective mitochondria. (Incidentally, defective mitochondria are to blame for some cases of moderate to severe autism – not fatal, in this instance, but nevertheless, very disabling.)

    If there is no destruction of a fertilised ovum or ova involved, there can be no objection on that ground, and nor can there be any objection on the grounds that the resultant hybrid is a chimaera, which would be the case if non-human nuclear or mitochondrial DNA were employed.

    However, I do foresee some difficulty arising, given that the procedure entails nuclear DNA from one person substituting for that removed from a cell taken from another. The nucleus may be regarded as the Captain of the cellular ship. The nuclear DNA ‘communicates’ with the ribosomes – the cell’s protein factories – by means of messenger RNA, which locks on to the ribosomal RNA and ‘tells’ it what type of protein the nucleus wants made. The ribosomal RNA then assembles the amino acids (the building blocks of proteins) at its disposal and starts to construct the specified protein.

    Neither the messenger RNA nor the ribosomal RNA are universal in character: they are specific to the individual, and correspond to that individual’s nuclear DNA.

    Taking the nucleus from one cell and putting it in charge of another is thus like relieving a Captain of his command part-way through a voyage, and imposing a new and entirely unfamiliar Captain on the crew. This may well be a recipe for mutiny. A newly fertilised ovum is a cell that, quite naturally, is already having to get used to half its nuclear DNA coming from an unfamiliar source. Make all of it unfamilar and the crew may well revolt – with potentially disastrous consequences. It is no surprise that most attempts to achieve fertilisation of these ova failed, and the cells died.

    There are good intentions and then, I am afraid, there are unintended consequences. What if the result of this procedure is a baby born with even more terrible disabilities than those the doctors are trying to prevent?

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