A university researcher has claimed victory for his theory that criminal behaviour is due to a genetic disorder after an Australian appeal court quashed a custodial sentence on a 15-year-old girl.

Melvyn Wall, PhD supervisor in the department of postgraduate education at the University of West Australia, argues that the majority of recidivist crime has its origins in a genetically based and preventable disorder.

He claims his research is backed by North American medical studies which show that children diagnosed as having attention deficit hyperactivity disorder are more likely to have a genetic defect than normal children.

Dr Wall is to take his theories to Chicago and the United Kingdom later this year.

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The judiciary and the courts in Australia are, says Dr Wall, ahead of world leaders in recognising the disorder as a mental illness for which offenders need treatment, which if given earlier might have prevented their crimes. He believes it is only academic criminologists who disagree with the theory.

Dr Wall's controversial view has been given a huge boost by the Australian court of appeal's acceptance of his diagnosis in quashing a custodial sentence.

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The appeal court judges said that had the 15-year-old convicted criminal been referred for diagnosis earlier she would "most likely" not have been involved (in crime), says Dr Wall.

In the next issue of the Journal of Crime Prevention of Australia, Dr Wall will differentiate between two types of delinquency.

The first type, "Life-course-persistent delinquents" are those with severe and early onset attention deficit hyperactivity disorder recorded from age three years or even younger, who if not treated may persist in a lifelong career in crime.

The second type are "adolescence-limited delinquents", who do not have the disorder, whose delinquency peaks at about 18 years, followed by a marked decline.

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Dr Wall began appearing early last year as an expert witness in criminal cases involving juveniles affected by the disorder. Following the first of his cases, after a judge had initially sentenced a juvenile to nine months custody on serious theft and assault charges, the court of appeal allowed his diagnosis to be a mitigating factor in quashing the sentence.

Dr Wall said he believed his trial evidence and the judgment set a precedent in Australia, and in half a dozen cases following this one his expert argument has not been challenged.

Dr Wall plans to visit the UK in November to talk to British academics and doctors after delivering a paper at a conference in Chicago.