Big news from the Institute of Mental Health and the West London Mental Health Trust suggesting not only that grandmas don't know how to suck eggs but that there’s much less of it – mental health – around than we imagined. Perhaps imagined isn’t the right word. One thing people with Personality Disorder don’t have is delusion. It’s practically the sole defining characteristic – at least the only symptom not mentioned. At least 4 per cent, or possibly 13 per cent of us suffer from it. In fact, the definition is so broad that it may be we all suffer from it, all of us who don’t actually see things that aren’t there when we’re awake and not drunk or drugged.

A personality disorder is defined as a pattern of behaviour that deviates markedly from the individual's culture... Those with personality disorders repeatedly behave in a way that is not acceptable to the community that they live in and cause distress to themselves, or others.

The rest of the world, I'm told by a sceptical friend in the psyching business, can be assumed to be schizophrenic, bipolar or schizoaffective.

Personality disorder was the diagnosis that troublesome girls and women received in the 1950s and 60s – anyway, I did. Mine was borderline, but you can also have it in paranoid, anti-social and narcissistic flavours. I’ve never been quite sure whether it was my personality that was borderline, or if the disorder itself was only mild and therefore borderline.

Why, when it's such old hat, does the BBC find this to be news: as in new, real or to be seriously considered by people who want to know what is going on in the world? Because new categories have been elaborated: you can now divide the types into Odd/Eccentric, Dramatic and Anxious. Symptoms include ‘having an unusual appearance’, fearing ‘negative evaluation’, having ‘unstable moods’ and feeling ‘inadequate in social situations’. Anyone without the symptoms, you might suppose, has no personality at all, but there doesn’t seem to be a No Personality Disorder, a condition I’ve spent very much more time worrying about, both in myself and quite often in some of those I come across in print.