When it comes to sexual crimes, men are nearly always the predator. But there have been rare cases of female sexual deviants.

John (not his real name) was 15 when he was molested by his mother. He and his younger sister were living with their mother, who was divorced from their father.

It was the girl, then four, who raised the red flag and told their father that 'mum was touching kor kor (elder brother)'.

She added that their mother also showered John and would touch him in the process.

When confronted, the mother declared this to be untrue.

The father eventually took custody of both children, and the case never went to court.

The incident, recounted by Dr Carol Balhetchet, director of youth services at the Singapore Children's Society, happened in 2007. She learnt of the incident during counselling when the mother applied for a 'beyond parental control order' on her son.

A study done by the Institute of Mental Health (IMH) on child sexual abuse in Singapore showed that of the 38 cases the clinic saw in 2001, all perpetrators were male except two. They were female domestic maids.

Social workers and counsellors said female perpetrators are very rare, especially in a family situation.

'Perpetrators want dominance and control over their victims and this happens more in males,' said Dr Balhetchet.

'When females become mothers, their instinct is to protect,' she added.

It was reported in The Straits Times last week that a woman in Ireland was jailed for seven years after forcing her teenage son to have sex with her, and for abusing and starving her other five children in a rat-infested bungalow.

The boy, now 19, was forced to have sex with his mother, now aged 40, on four occasions over a six-year period.

This article was first published in The Sunday Times on Feb 1, 2009.