AT HOME, Corrine behaves like a normal seven-year-old. She is chatty with her parents and her sister and loves telling stories to her grandfather.

At school, though, she is known as 'the girl who doesn't talk'. She freezes when a stranger speaks to her and stares blankly when asked for her name or age.

She kept silent through two years in kindergarten and now, four months into Primary 1, she has still not uttered a word to her teacher or classmates.

At first, her parents thought she was just shy. Her mother said: 'I didn't think it was a big problem. I just thought she was a little reserved when out in public.'

But once she entered kindergarten, they realised it was much more than that.

Her teachers said she was not speaking up in class. When she needed to go to the bathroom, she would rather hold it in or wet herself than ask for permission.

Also, she did not seem to know her ABCs - and yet she read avidly.

Corrine's parents took her to a child psychologist, who diagnosed her problem as selective mutism, a little-known anxiety disorder.

A child with this can understand what is being said and speak normally at home but becomes unable to talk in specific situations, such as in school or in public.

The Child Guidance Clinic (CGC) at the Institute of Mental Health (IMH) and psychologists in private practice have seen more such cases in recent years.

The CGC alone has diagnosed 115 cases in the last five years. Three years ago, it diagnosed 18 children; last year, the number nearly doubled to 34.

The Education Ministry said 65 students in mainstream schools were diagnosed with the disorder in 2007; last year, the figure was 80.

Dr Daniel Fung, who heads IMH's Department of Child & Adolescent Psychiatry and the Child Guidance Clinic, said the condition often goes undetected because awareness of it is still low and because parents and teachers think the child is just shy or anxious about school.

But there is a difference between ordinary shyness and selective mutism.

Dr Fung said: 'A shy child, given a familiar environment and some encouragement, will eventually open up. But a child with selective mutism will remain mute.'

A 2002 study in the Journal of the American Academy of Child and Adolescent Psychiatry said the condition affects about seven in every 1,000 children, and strikes girls more than boys; it becomes obvious when the child starts pre-school.

The severity varies. Some children are completely non-communicative, others may use gestures and nods.

At one time, psychiatrists thought the condition was a child's way of showing defiance, but they now believe it has its roots in social anxiety.

Treatment involves lowering the patient's anxiety through medication such as Prozac and helping the child become more communicative in stages.

Dr Fung said it is important that parents of such children do not keep harping on speaking up because that would only reinforce the anxiety.

Occupational therapist Yael Sasson of Dynamics Therapy Centre, a private clinic for children, said the biggest challenge is to move the child from non-verbal to verbal communication.

She suggests getting the child to read at home, recording the session and playing it back in school so the child gets used to hearing his voice and overcomes the anxiety.

'It is a big step when the child starts whispering the answer to a friend in school or even to the teacher,' she said.

Most children get better in a year, said Dr Fung, but some do not overcome it.

One of his patients came to him at age 11, and despite medication and behavioural modification, the boy got no further than whispering to him, and was selectively mute even in university, where he studied computer science.

Corrine, meanwhile, has made slow progress with treatment.

Two weeks ago, she began using a book with symbols in it which she showed her teacher to indicate what she needed.

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