Ever since genetics became sexy, I've been terribly attracted to the idea of gene therapy. It has a sort of gentle, masseur feel to it. I picture all my soft and blobby genes swishing around in an aromatic bath of blue water, getting clean and therapised. My husband, on the other hand, is upset at the way some supermarkets are offering perfect, genetically engineered fruit and vegetables. He bemoans the lack of seasonality and connects it with the arrival of the perfect, tasteless bunch of baby grapes. I love it all - the perfection of the baby grape, its size and the fact that it's so expensive. All this appeals to my inner need for new and exciting forms of retail therapy. I just like therapy - anything to make it all better.

Of course, you can't buy gene therapy in the supermarket yet. Contrary to my view of the world as a giant supermarket, it doesn't come in bottles. And it's all very well being seduced by the appliance of science over tasty morsels, but the idea of the perfect grape sours when you think of the possibility of the perfect person.

The question of the perfect person raised its ugly head at the Scottish Regional Fragile X conference recently. Although it's one of the most common inherited forms of mental handicap, little has been known about Fragile X until now. One of the guest speakers addressed the issue of prenatal screening and gene therapy for Fragile X foetuses. I think it means that if, let's say, in 20 years' time, someone like me who has one Fragile X child already, becomes pregnant, gets screened and discovers the next baby is mentally handicapped as well, a brave new world of opportunity and choice opens up: have the baby as is, have an abortion, or offer up the foetus to allow that all-important gene on the X chromosome to be "turned on" again. We can imagine the consequences of the first two choices. And the third? Hello perfect, "normal" person - a blonde, I imagine.

When I compare Henry, my son who has Fragile X and suffers from "global development delay with behavioural difficulties", to a genetically engineered grape, I'm glad this gene therapy is not around yet. But when I think of him in a supermarket, homicide comes to mind. Last weekend, for example, both my boys insisted on coming shopping with me - Henry, who's four, because he thinks I'll buy him sweets, and Lewis, eight, because he thinks I'll buy him anything he wants with the right amount of pressure. I'm already a bit sweaty, but it's my angst not theirs, I keep telling myself. For God's sake, it's only the supermarket. I spend the journey telling them what's going to happen if they don't behave themselves. Lewis looks sullen and Henry, who suffers from a serious speech repetition disorder, repeats "behave selves" maybe 50 times.

We get through fruit and veg without a hitch. The trouble starts when Henry decides we can't have any of the things I've put in the trolley. He starts shoving them back on to the wrong shelves in a fierce temper, shouting "No, Mummy" at the top of his voice. Nobody's looking, apart from everybody. They think it's funny until they see it's not. "Shall I buy you some sweeties, darling," I say softly, tightening my grip on his wrists. "No, Mummy," he shouts.

Lewis is dying with embarrassment and heads off to another aisle. I let Henry sit on the floor and open the packet of biscuits he's tried to jam between the tins of beans. While his distress has reached a pitch likely to make him sick, I am assaulted by another, familiar cry of pain. Yes, it's Lewis, coming round the pasta sauces holding his head, which has been butted in a collision with a small boy's toy rifle. The boy was looking for someone to kill. Lewis was looking for bran flakes. Ah, well. We head for the check-out, leaving aisle No 42 littered with broken eggs, biscuit crumbs and the odd piece of salami. Oh, and two supermarket staff who clearly would call the social services if they knew the number, but who clear up the mess instead.

By the time we reach the till, Henry's no longer sure that he can allow the trolley to be emptied. I try kissing games on the left side of his neck, while using my right hand to unload. Henry fights back and our "packer" starts poking him, as adults do to small children who are in a state. "What's the matter with you, then?" she says, "Got out of bed the wrong side, did we?" If she carries on like this he'll be sick on her. Meanwhile, I'm fumbling for my Reward Card (ironic, isn't it?) and Lewis's head looks all peculiar. "Where'd you get that funny mark on your head?" I ask in a normal voice. "It's where I got hit with the gun, Mum, remember?" Ah, yes.

Because Fragile X is incurable, I have to find ways of changing Henry's behaviour by monitoring what we do to him and what situations we put him in. And while we must expect weird stuff from him, it doesn't mean we have to accept it. Nor should we accept other people's anger and intolerance towards him and, by association, towards us, the parents or carers. So, in the circumstances, I think it would be best if the whole family stopped going to the supermarket and simply waited for the perfect, all-round, once-a-day nutritional pill to be developed. Or should I say engineered?