A "happiness gene" which has a strong influence on how satisfied people are with their lives, has been discovered.

Those with two sets of the gene - one from each parent - are almost twice as likely to say they are satisfied with life, compared to those who lack a copy.

The gene, called 5-HTT, is responsible for how well nerve cells manage to distribute serotonin, a chemical produced by the pineal gland in the brain which helps control mood.

People with low levels of serotonin - itself nicknamed the 'happiness drug' - are known to be more prone to depression.

Now behavioural economists at the London School of Economic and Political Science have found evidence that people with the "functional" variant of the 5-HTT gene tend to lead happier lives.

Jan-Emmanuel De Neve and colleagues asked more than 2,500 people in the US about how satisfied they were with life, and also analysed their DNA for presence of the gene.

The 5-HTT gene provides the "operating code" for transporting serotonin in neuron cell walls.

The 'long' version of the gene leads to more serotonin transporters in these walls, the 'short' version less of them.

As we inherit a set of genes from both parents, the possible combinations of this are 'long-long', 'long-short' or 'short-short'.

The researchers found that 69 per cent of people who had two copies of the gene said they were either satisfied (34) or very satisfied (35) with their life as a whole.

But among those who had no copy of the gene, the proportion who gave either of these answers was only 38 per cent (19 per cent 'very satisfied' and 19 per cent 'satisfied').

The study is published today (FRI) in the Journal of Human Genetics.

Mr De Neve, a former Fulbright scholar at Harvard who has published papers on subjects as varied as EU integration and prize-linked savings like Premium Bonds, said: "It has long been suspected that this gene plays a role in mental health but this is the first study to show that it is instrumental in shaping our individual happiness levels.

"The results of our study suggest a strong link between happiness and this functional variation in the 5-HTT gene.

"Of course, our well-being isn't determined by this one gene - other genes and especially experience throughout the course of life will continue to explain the majority of variation in individual happiness.

"But this finding helps to explain why we each have a unique baseline level of happiness and why some people tend to be naturally happier than others, and that's in no small part due to our individual genetic make-up."