Monday, October 16, 2006

Prevention better than the cure? #1

In the comments following my post about T4, Mary recounted a conversation with an acquaintance about the prospect of Mary having children at some point. This exchange concluded;
Clearly, this person had a number of 'issues'. As Mary had already pointed out to them, she doesn't even have a heriditary condition. But I wanted to write a few things about the prevention of disability, and genetics is a good place to start.

First off, to recap, let’s return to the primordial goop. Cells are beginning to form. Very many different cells, with a great variety of qualities would have come into being and gone again. The very first one to make any difference to anything was the one that divided into two cells, where those two cells divided again into four. But others did exist.

And this represents the only ‘order’ in the otherwise random process of evolution; the code we know about is the code that just so happens to have got this far.

Frankly, the fact that you are sitting there, reading this, is a miracle. Your genes just happen to have been reproduced over squillions of generations, through all sorts of mutations and incarnations; they survived when many godzillians of others came to a full stop. You are an evolutionary success story – even if you are severely disabled, happen to be facing premature death or find yourself unable or disinclined to have children. You are really a rather amazing creature just for existing on Earth in 2006AD, four billion years since that first cell division. Don’t waste it!

So what if you do have dodgy genes? There are five possible explanations for why you possess any given piece of genetic code;
1. It does something big or small which enabled your predecessors to survive and successfully reproduce in the particular set of circumstances they found themselves in.

2. It has never done any harm and has survived purely by chance.

3. It mutated into what it is at the point of your conception.

4. It does some harm but not enough to seriously impair survival and successful reproduction.

5. You were created in a laboratory by a mad scientist, which is why you have oak leaves instead of underarm hair.

A proportion of genetic conditions fall into category (3). Mutations are happening all the time and sometimes a small change can make a massive difference – like a typo in an HTML document. Which makes it sound like a mistake. Mutation is not a mistake. It is just a random but essential event without which we would still be single-celled organisms.

This means that, for example, there will be a proportion of people with Downs Syndrome in every generation that is conceived; this mutation is just something that happens. There are risk factors such as the age of the mother, but still most Downs babies are conceived to women under thirty-five simply because most conceptions take place in women of under thirty-five.

Anyway, far more genetic conditions come into the (4.) category; the mutation did harm in the past, but not enough to seriously impair survival or reproduction. This can mean one or a combination of two things.
(a) The mutation frequently causes illness or impairment, but it is either so mild not to make a great deal of difference or it does not usually manifest until middle or old age.

(b) The mutation only causes illness or impairment some of the time. Most people who carry the affected bit of code will be completely unaffected.
Category (a) conditions which cause significant long-term impairment are fairly unusual. Huntington’s Disease would be an example of this; the affected gene almost guarantees illness, and having a parent with HD gives you a 50-50 chance of getting sick yourself, only the average age of onset is about forty, by which time most people will have established families.

The vast majority of conditions with any genetic cause come under category (b). Even with something like haemophilia, the basic pattern of which we all know about from the history of our Kings and Queens, only one out of every four children a carrier might give birth to is likely get sick (i.e. one in every two boys will be affected, one in every two girls will be carriers).

Most conditions are far less prevalent within affected families, partly because most conditions require a combination of genetic and environmental factors in order to manifest.

We know, for example, that our genes are somehow tied up with the development of Multiple Sclerosis. We know this because where you have a close relative with MS, your chances of getting sick yourself increase from about one in 750 to as much as one in forty. Which is still only one in forty.

Perhaps most notably, if you are a monozygotic twin - if you have exactly the same DNA as a person with MS - then your chances are increased to one in three. Which shows that this condition is not purely about genetics, or else it would be one in one. Why one twin might get sick where the other does not could be due to all number of subtleties we are yet to understand.

This pattern is similar with schizophrenia, lupus, certain cancers and a great many other conditions. Most disabled people have no reason to expect to have disabled children.


Agent Fang said...

There's a 50-50 chance my condition would be passed on to my children. Except I prefer to have dogs, so I'm not going to have any children. When people ask me THAT question in relation to the situation, I point out number 4 It does some harm but not enough to seriously impair survival and successful reproduction. And also that the world is a richer place for diversity, whether it be religious, racial, sexual or genetic... :0)

James Medhurst said...

There are other possibilities. For example, some combinations of genes, that aid survival and reproduction, can lead to less favourable outcomes when they combine in different ways. An example is the genetic link between schizophrenia and artistic creativity. This means that it is impossible to eliminate the supposedly negative traits without getting rid of the positive aspects as well.

Many Nobel Laureates, including the geneticist James Watson, have had disabled children and yet people are still willing to pay a fortune for their sperm!

Anonymous said...

You should do a little research and look up Brie Walker, and Jim Lamply(sp on both?). Brie was a news anchor for a major s california tv station that had a disability that mader her hands and feet look like crab claws. Her husband Jim is a famous sports anouncer. They married many years ago and decided to have kids knowing that a strong chance existed the disability would be passed along. It created a storm of controversity in s cal press and talk radio about the disabled having kids. It ended up being a valuable discussion.

The Goldfish said...

Fang - the world is indeed, a richer place.

James - this is true. I attempted to explain all this, but then decided they still counted as category (1). We have very many genes which help us in one regard and hinder us in another, but if they have helped more than hindered (in the particular circumstances that organism finds themselves in), they survive. Frankly, a human being is not the optimum design for standing on its hind legs; the fact we do that condemns a certain proportion of us to back pain and injury. There are also things which helped at one point, but didn't go away when they were no longer useful. Perhaps I should write a bit about this too, but genetics is a bit of a pet subject and I could contribute toward impairment by boring everyone stiff. ;-)

Al - I'll have a rummage, see if I can find that story thank you.

BloggingMone said...

I agree to Agent Fang, diversity is very much needed as it also creates different views of the world, which can only be a good thing. As you pointed out most of the disabilities are not hereditary to 100%. And sometimes it is ablessing that a disabled child also has disabled parents. When I sit in class at a deaf school, it only takes me 10 to 15 minutes to spot out those children, who have got deaf parents. They usually are the brighter ones, because they have a well functioning family communication and a lot more self-esteem.
I think to a large part it is a problem of society in general and of doctors in particular. Mothers are recommended to have checked at a very early stage of their pregnancy, wether the child is likely to have a disability or not. If so abortion is recommended quite openly. If mothers decide agains being tested, then there is a great danger of being accused to have given birth to a disabled child, even though having a child like this is no longer necessary.
This is a problem we should be working on instead of spending billions on all kind of genetic research and so-called medical progress.

Charlesdawson said...

Goldfish, I would like to add to your list of mutations, those which have a survival value in some circumstances (which is why they continued to be bred) but a negative survival value in others.

Such as sickle-cell trait and the minor thalassaemias, both of which protect against some forms of malaria and are therefore of value in contries where malaria is endemic.

Unfortunately, inbreeding means that instead you get a double dose of the genes, which results in sickle-cell anaemia and thalassaemia major both of which are serious, disabling conditions and in extreme cases fatal.

There may well be other conditions which also have this built-in, we don't know yet, but say if it were possible to eliminate the gene for Huntingdon's and it was found that all along it had conferred protection against, say, some untreatable forms of cancer?

Timmargh said...

*raises hand ... with difficuly*

I'm a mutation but I'm not a monster ... honest!

Like Fang there's a 50/50 chance of my condition going to my children but, also like Fang, I prefer dogs! Kids are great when they're someone else's because you can hand them back when they start crying and I'm far too selfish with my time to take on the responsibility of a tiny life to look after.