Christopher Wolstencroft, aged seven, suffers from fragile X syndrome, a genetic disorder that makes him hyperactive and means he is unable to concentrate for long. Two years ago he was prescribed folic acid, a B vitamin more usually recommended to women in the early stages of pregnancy to prevent spina bifida in their babies.

Christopher's mother, Claire, says he has responded 'brilliantly' to the vitamin treatment. 'He's generally calmer, more willing and amenable, and more in control of himself,' she says. 'He can maintain his attention for longer, which is important for a seven-year-old boy who's struggling to learn to read.

'It's not a miracle cure - it doesn't make him normal - but life would be very difficult if he wasn't taking it.'

Pioneering work on the use of folic acid as a treatment for children with fragile X syndrome is being carried out by Dr Jeremy Turk, a child psychiatrist at St George's Hospital Medical School in London. He estimates that about two-thirds of children with this condition can be helped by taking the vitamin. He also believes it might benefit the one in 20 children who do not have a genetic disorder but are simply hyperactive. 'I plan to do research to answer that question, and I believe the answer could well be yes,' says Dr Turk.

Fragile X syndrome affects about one in 1,000 children. As well as hyperactivity and inattention, it causes delayed development, mental impairment - ranging from subtle learning problems to severe handicap - and autistic behaviour, such as avoiding eye contact and flapping or biting the hands. Boys are affected more often, and usually more severely, than girls. An accurate DNA test to detect fragile X has been available since 1991, but many cases in adults and children are still unidentified by doctors.

Last year the Department of Health advised women to increase their intake of folic acid before pregnancy and in the first 12 weeks after conception to prevent spina bifida and other serious neural tube defects in unborn babies.

Although fragile X is caused by a chromosome defect and has nothing to do with a deficiency of folic acid, research from the United States has suggested that large doses of the vitamin - much larger than those contained in supplements from health food shops - seem to relieve some of the symptoms. A major double-blind trial at the Children's Hospital, Denver, details of which were published in the American Journal of Medical Genetics in 1986, found that there were significant improvements in fragile X children who had taken the vitamin rather than a placebo.

Dr Turk prescribes a dose of five milligrams twice a day. 'I was excited by the positive results in the US because hyperactivity is such a problem and there are so few treatments,' he says.

'Folic acid doesn't do anything for the children's intellectual level, or for their speech and language problems, but it helps their poor concentration, restlessness and distractibility, and enables some to perform better in IQ tests,' Dr Turk says.

In the US, hyperactive children, including those with fragile X, are often given stimulant drugs such as methylphenidate (Ritalin), an amphetamine. It is estimated that as many as a million American children take Ritalin to control hyperactivity and 'attention deficit disorder'. But in Britain, using drugs for behavioural problems in childhood is frowned upon and medication is rarely used.

Folic acid has been found to have a similar effect to Ritalin, and in Britain would be more acceptable as a form of treatment for hyperactivity. It is readily available, cheap and already present in a healthy diet. Dr Turk says he knows of no adverse effects although in large doses it is not suitable for children with epilepsy.

A stimulant may seem an odd thing to give a hyperactive child but, as Dr Turk explains, it acts by improving their concentration, rather as others might have a cup of strong coffee to help them focus on a particular task. It is thought that the vitamin enhances the activity of neurotransmitters in parts of the brain which control concentration and which, in hyperactive children, are under-functioning.

One of the features of fragile X children is that they suffer from 'information overload': they cannot block out auditory and visual distractions. Treating this can make an important difference to the behaviour of these children and their families.

Hannah Bayly, aged eight, also has fragile X and has been taking folic acid for 18 months. 'She hated shopping and crowds. She used to throw herself on the floor and scream,' says her mother, Jo. 'But when she started taking the folic acid there was an instant difference, a dramatic change in her personality. She is much calmer, more able to concentrate, and she takes in what you are saying. Before, she was in her own little world and often wouldn't respond. It's helped her at school as well - she is in tune with what's going on around her.

'If I forget to give her the folic acid she gets excitable and starts racing around, back to the way she used to be.'

Dr Turk has carried out a double-blind placebo-controlled study on 15 children and is currently analysing the results. He is planning to carry out further research into whether other hyperactive children can benefit from taking the vitamin.

'Some parents are convinced it has made a real difference to their children's behaviour. As well as being much calmer, in some cases the children are also happier. A child doesn't actually enjoy being out of control and racing around,' he comments. 'It's also helped some children who sit at the back of the classroom daydreaming the hours away.'

About one in 200 children is thought to be severely hyperactive, while as many as one in 20 is 'borderline'. Sally Bunday, of the Hyperactive Children's Support Group, is critical of the use of amphetamines for such children and warns of serious side-effects, but feels vitamin treatment would be more acceptable. 'Do we really want children on powerful drugs?' she asks. 'There are more positive ways of helping children that are not going to do them any harm, and we would feel much happier about folic acid.'

Dr Turk stresses that folic acid needs to be prescribed and monitored by a professional, and should form part of a package of care, including special education, psychological techniques such as behaviour modification and, possibly, family therapy. 'Folic acid is a further means of tackling an important problem, and it could well be very significant,' he says.

For more information contact The Fragile X Society, 53 Winchelsea Lane, Hastings, East Sussex, TN35 4LG, enclosing an SAE, or telephone 0424 813147.

(Photograph omitted)