why do humans behave so differently from one another? Behavioural scientists say that a study of this variation is a rather controversial one even while it is exciting. They say that if you look hard enough, genetic influence on behaviour can be easily identified. For example, variation in personality traits and even diseases like schizophrenia and alcoholism have been linked to genes inherited from parents. In addition to the other groups of people with deviant behaviour, neurotics will have one more worry on their minds - the genes they have inherited.
A report by Peter Lesch and his colleagues of the department of psychiatry, University of Wurzberg, Germany, working with scientists of the National Institutes of Health (nih) , Bethesda, us , report that people who have inherited one form of a gene on chromosome 17 are more likely to become anxious.
This is the first study of its kind linking genetic variation with anxiety and should be a cause of concern for those who keep worrying about things. According to Dennis Murphy of the nih who led one of the teams, as many as 15 genes are suspected to influence people's tendency to worry. Upbringing and circumstances, however, compound the problem of genetic influence on behaviour.
But what the researchers were able to prove now is that the amount of neuroticism, a personality trait that can be quantified by testing, is influenced by two alleles of a gene encoding a transporter for the neurotransmitter, serotonin - the chemical messenger whose balance in the brain is vital for the control of moods. One allele results in more protein and therefore, more neuroticism and the other less neuroticism. The research teams examined dna samples from hundreds of volun- teers. To their utter frustration, they did not find any variation in the sequence of the transporter gene itself.
But what they found interesting was a stretch of neighbouring dna responsible for spurring the gene into action. This 'gene promoter' is inherited in two forms - l and s . The gene influencing the production of a protein that transports serotonin is called l for long allele containing 44 amino acids. As a result, l allele is transcribed more efficiently than the short ( s ) allele and more proteins are made, leading to as much as twice the serotonin uptake. Between them, the two alleles control the levels of serotonin.
The scientists found that people with 'sluggish' version of the gene promoter scored higher in personality tests for neurotic behaviours such as worrying, fear and pessimism than people with the more active version. In fact, psychiatrists prescribe drugs for extreme anxiety, drugs that will act on the transportation of serotonin, thus controlling its level. If the action of the drugs can alter the mood of the people, the researchers reasoned, there might a natural variation in the protein between individuals who react to similar situations with varied levels of anxiety. So they examined the gene encoding the protein to see whether particular dna signatures are linked with neurosis in people.
Commenting on this study, David Goldman from the National Institute of Alcohol Abuse and Alcoholism, nih, us , said, "The number of potential candidate genes - genes that can in any way alter brain function - is formidable." Even while cautioning about the pitfalls of any study linking genetics to behaviour, Goldman concedes that this work is a significant milestone towards the understanding of the complex issue of deviant behaviour. "Identification of candidate alleles is one important approach for elucidating the origin of the mechanism of measured heritabilities of behaviour traits and psychiatric diseases," he said.