Gene may help doctors identify patients at risk of schizophrenia

Scientists have made a breakthrough in understanding the biological basis of schizophrenia, the most common severe mental illness in Britain. The findings could result in earlier diagnosis in children and young people, and lead to the development of new drugs and better treatment.

A study has found that a genetic defect in some people can trigger a dangerous increase in levels of a natural brain chemical called dopamine, which may lead to schizophrenia.

Although the discovery applies to only a small proportion of people who develop the illness, scientists who conducted the study believe it could result in a fundamental shift in the understanding of the condition.

"The hope is we will one day be able to identify the highest-risk groups and intervene early to prevent a lifetime of problems and suffering," Allan Reiss, of Stanford University in California, said. "As we gain a better understanding of these disorders, we can design treatments that are more specific and effective."

About one in 100 people will suffer from schizophrenia at some time in their lives and the annual cost to the nation in health care is estimated at more than £2.6bn.It is characterised by changes in thoughts, perception and behaviour, and typically strikes people in their 20s or early 30s. One in five sufferers make a full recovery but an equal number need expensive, long-term treatment. The rest recover in part but may suffer relapses.

Scientists do not know what causes schizophrenia but there is strong evidence for a biological or genetic basis.

The general population has a 1 per cent chance of developing the illness. The risk increases to 10 per cent for the close relatives of a patient, and for identical twins rises to 47 per cent if one is already diagnosed.

The study, published in the journal Nature Neuroscience, investigated 24 children who suffered from a genetic mutation known as a deletion on one chromosome. It is known that about one-third of children with this deletion to part of chromosome 22 will develop schizophrenia. The deletion occurs in one in 4,000 births.

"We have strong evidence that this deletion is a major risk factor for the development of schizophrenia or related psychotic conditions," Dr Reiss said.

The study found one of the genes on the part of the chromosome that is missing is responsible for a protein that degrades dopamine, a critical chemical messenger, or "neurotransmitter", in the brain. Children with the deletion suffer higher-than-normal levels of dopamine, interfering with what scientists call the "Goldilocks effect", when it is important not to have too much or too little, but just enough dopamine.

The scientists followed the children for five years. As expected, about one-third developed schizophrenia in that time. "Although this deletion probably causes less than 5 per cent of schizophrenia cases, it's the only well-defined genetic risk factor we have right now," Dr Reiss said.