Experts who found a link between depressed parents and children who develop mental health problems have been given a £1m grant.
The grant will fund research into children aged 10-17
The funding, from a medical charity, will help the team from Cardiff University study the reasons behind the link.
It will also fund a study of children aged 10-17.
It is hoped the five-year project will lead to improved diagnosis and earlier treatment of "at-risk" teenagers.
Project leader Professor Anita Thaper said that by 2020, depression would become the second largest cause of medical disability in the world.
She said most adult sufferers started to show symptoms during adolescence, but the problem was rarely identified at that stage.
"Our pilot study showed that there are alarming numbers of children with depression, who are not being picked up by the services," she said.
"The 2m UK children exposed to depression suffered by their own parents are at especially high risk.
"We want to find out how we can identify those as greatest risk so that preventative strategies can be targeted on them."
The £993,392 award from the Sir Jules Thorn Trust will also fund a software package to help GPs target teenagers at the earliest possible stage.
Researchers will try to establish the age at which adolescent depression starts, what affects its course over time, why it is becoming more common and its effect on parents.
The project will also look into the social and genetic factors linking parental depression to teenage mental health problems, as well as the symptoms.
Prof Thapar said the award was a "fantastic boost" for research in the field because mental health problems in children were often overlooked.
Feelings of helplessness and hopelessness
Feeling useless, inadequate, bad
Feeling vulnerable and being over-sensitive to criticism
Sense of guilt and the loss of energy
"We know there is a link between the illness in parents and children - we just don't know why," she said.
"Depression is now a real problem. A chronic episode is extremely disruptive to the sufferer's life, but it is often not recognised and is extremely difficult to treat.
"This project will not only be scientifically valuable, it will produce direct benefits for the treatment of adolescents and adults with depression."
The Sir Jules Thorn Trust was established in 1964 to support medical and humanitarian projects.
Cardiff was one of several universities invited to bid for the grant.