Researchers have pinpointed a section of DNA which they believe is responsible for depression.
This particular region – known as chromosome 3p25-26 – contains up to 40 genes, and one or more probably causes the condition.
Over the next year the scientists hope to carry out more detailed work to try and pinpoint exactly which gene is responsible.
Up to one in five people will suffer from depression at some point during their lives.
Although depression is often triggered by traumatic events, such as death/grief, or divorce, researchers have long known that certain people are more susceptible to depression.
Depression Gene Study
Researchers studied the DNA of more than 800 British families with two or more siblings with depression.
At the same time another team of scientists from the Washington University Medical School in St Louis, the US, looked at 91 families in Australia and 25 families in Finland.
Depression Gene Hasd a Genetic Link
New DNA findings may suggest that depression runs in families, with people inheriting the genes from their parents
The findings show that the depressed siblings had the same genetic variations in the same section of their DNA.
This would suggest that depression runs in families, with people inheriting the genes for depression from their parents.
Lead author Gerome Breen, from the Institute of Psychiatry, Kings College London, said: 'In a large number of families where two or more members have depression we found robust evidence that a region called chromosome 3p25-26 is strongly linked to the disorder.
'These findings are truly exciting as possibly for the first time we have found a genetic locus for depression.
'Though these findings will not result in a test for depression they will help us track down specific genes that are altered in people with depression.
'This breakthrough in understanding the risk for depression may get us closer to developing more effective therapies for depression though patients should not expect to see these available for 10-15 years.
'Any one of 40 genes in chromosome 3p25-26 could be responsible so we are currently conducting detailed sequencing examinations in 40 of the families involved, to identify specific genes and variations that are causing the linkage. Results of these studies should be available next year.'
Marjorie Wallace, chief executive of the mental health charity Sane, said: 'It is very exciting that there seems to be progress finding the gene involved in some people developing depression.
'However, we are still some distance from identifying the "culprit" rogue gene.'