Girls suffering from attention deficit hyperactivity disorder (ADHD) are often not getting correctly diagnosed - and it may because the condition manifests differently from in boys, NHS experts say.

Up to 5% of school-age children are thought to suffer from ADHD, a condition characterised by a group of behavioural symptoms including hyperactivity, difficulty concentrating and impulsiveness.

But boys are far more likely to get a diagnosis and support for the condition than girls.

New draft guidance from the National Institute for Health and Care Excellence (Nice), the NHS clinical authority, suggests that girls with the condition are being overlooked.

"Among the possibilities are that boys present with more obviously disruptive behaviour," she said.

Some doctors believe that boys are more likely to display what are thought of as the "classical" signs of ADHD including hyperactivity and aggression.

They suggest that girls are less likely to be extremely obviously physically hyperactive, but suffer more with inattention and keeping focus on tasks.

It's not clear why there may be differences in the genders, and whether it might be partly down to socialisation.

Nice's new guidelines say that more efforts need to be made to reach groups with ADHD who are currently being missed.

It says doctors should be informed about groups who are more at risk of the condition, including children born prematurely, those in care, and children with a family member who has also been diagnosed with ADHD.

People with epilepsy are also more at risk, as are those who have other conditions, such as autism.

Professor Mark Baker, director of the centre for guidelines at Nice, said the changes could make a real difference to children's lives.

The latest guideline also says children and young people should be prescribed drug treatments including Ritalin if ADHD is having a persistent impact on their daily life.

In previous guidance, Nice said these should not be routinely prescribed to youngsters.

It also advises against putting children with the condition onto restricted diets or cut out artificial additives and sweeteners, which some people believe help to manage the condition.

It said parents who think there is a link between poor behaviour and diet should be advised to keep a diary, while a dietitian and mental health specialist should be involved before any restrictive diets are introduced.