Out of America there is always something new. The latest example of its unparalleled contribution to medical progress is the announcement by the University of Washington that scientists have succeeded in removing the extra copy of chromosome 21 in cell cultures derived from a person with Down’s syndrome.   Since it is the possession of three, rather than two, copies of the 21st chromosome that defines Down’s syndrome, it is clear this breakthrough has startling potential for addressing a condition which is far and away the commonest form of congenital disability.

The senior gene therapy researcher on the project, Dr David Russell, was properly cautious: ‘We are certainly not proposing that the method would lead to a treatment for Down’s syndrome.

‘What we are looking at is the possibility that medical scientists could create cell therapies for some of the blood-forming disorders [such as leukaemia] that can accompany Down’s syndrome.’

Nonetheless, for parents of children with the condition (and I am one), this news inevitably raises the question: What does it mean to have a ‘cure’ for Down’s? And, perhaps more difficult, would we even want our children to be — for want of a better word — normalised?

There is, of course, an existing so-called treatment of the condition: elimination by abortion, following a ‘positive’ result in amniocentisis.

Yet this invasive method of inter-uterine testing carries a risk of miscarriage. This perhaps explained the headline two months ago over a report in the Daily Telegraph on a new non-invasive method: ‘Blood test for Down’s could save 300 babies’ lives a year.’ Clearly, the embryos with Down’s that were correctly identified and dispatched did not count as real babies.

This ‘eradication’ of Down’s syndrome (as another article on the new test cheerfully described it) is not actually a treatment at all. The condition would continue to recur with the same frequency as it always has done: all that would have changed is that the patients would never emerge.

Gene therapy, however, would be a genuine attempt at treatment and cure — but also colossally complex, at the outer fringes of the feasible.

Most genetic conditions being worked on by medical scientists tend to be those caused by a single gene — usually one mutation within one amino acid. But as Professor Roger Reeves of Johns Hopkins University Medical School told the New York Times last year: ‘With Down’s syndrome, you have an extra copy of all 500 or so genes on chromosome 21.’

Yet imagine if someone at Johns Hopkins or Washington really did discover a way of therapeutically removing all the extra genetic information within the 21st chromosome that causes the mental disability within the person with Down’s. Would this be an unmitigated blessing for either the child or its parents?

You might think so: but in a recent survey of Canadian parents with Down’s syndrome children, 27 per cent said that if there were a ‘cure’ for their offspring’s condition, they would not use it, while a further 32 per cent said they were unsure if they would take advantage of it.

This result was described as ‘surprising’ by the New York Times — but it is not really surprising at all. My 17-year-old daughter, who has the condition, is what she is; and that is the person her parents and elder sister know and love. If she were genetically re-engineered, would she be the same person?

She would certainly be very different — with the ability to count or read a clock; possibly even to penetrate the secrets of calculus. But those are not the sort of attributes which define what we love in those to whom we are closest.

This is one of the lessons that having Domenica as a child has taught me.

It is very easy, especially in high-achieving middle-class families, to confuse parental love with parental ambition. We slip into the conceit that what drives us to push our children towards academic or professional success is disinterested concern for their well-being; whereas, in fact, this is an extension of our own ambitions and even a form of self-love.

When you have a child with Down’s syndrome, all this social pride is stripped away — and what remains is the unconditional love which should be the birthright of all children.

This does not mean, of course, that children with Down’s are exceptionally fortunate. Domenica is sufficiently intelligent to know that she is different. I had hoped that she would not develop this level of self-awareness, but she has.

She experiences a sharp sense of social isolation, as hardly any of the friends she has made at school have ever included her in their extra-curricular lives, or invited her to their parties.

I understand that this is because Domenica’s interests and desires are more closely related to a ten-year-old’s than to those of her contemporaries, who would prefer to talk about sex rather than the latest Hannah Montana programme on the Disney Channel. So that is a sadness for her.

On the other hand, Domenica also exudes an uncomplicated love of just being alive, and she spends more time laughing uproariously about the absurdities of life than anyone I have ever met or am ever likely to meet.

I dislike it when others say ‘Oh, they’ — meaning all people with Down’s syndrome — ‘are such happy people’. Yet perhaps there is something in that condescending generalisation; and why would we want to regard it as something that needs ‘curing’?

In all this, it is important to bear in mind that Down’s syndrome is not a disease, infectious or otherwise. Neither, despite the lazy shorthand of some pseudo-medical commentary, do people ‘suffer’ from Down’s syndrome. It is true that people with disabilities, especially those that are visible to the naked eye, are often teased or bullied, and this certainly causes suffering to the victim.

But it is perverse to assert that the appropriate treatment for this form of suffering is that the stigmatised, rather than the stigmatisers, are the people who should be made to change their fundamental identity.

For the same reason, it is depressing that some parents of children with Down’s syndrome should feel it right to have plastic surgery performed on their son or daughter, so as to make them look more ‘normal’. This was the theme of a television documentary some years ago, called Changing Faces.

I recall watching it with horror. Partly, I suppose, this is because — like any parent — I see my own children as beautiful beyond compare (whatever anyone else might think). But also because, again, to force a child to have his or her features surgically rearranged in order to conform to some sort of social convention is to honour prejudice.

None of this is meant as a criticism of the attempts by American scientists to find a treatment for Down’s syndrome — especially as it presents itself as an alternative to the eradication policy more central to medical practice in this country.

Nonetheless, just as Americans tend to overuse anti-depressants in the vain belief that continual happiness is the natural state of mankind, they seem to have a national tendency to want to change anything that does not seem perfect.

That is a mighty force for progress: but it is not the secret of life.