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;

THEM: But you're ill, so there's obviously something wrong with your genes that let you get ill. If you got pregnant, your kid would just be another burden on taxpayers like me. You've got a social responsibility to put a stop to it.

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.