Could genes help unlock the reasons why we suffer from depression and anxiety?

• Video report by ITV News Science Editor Tom Clarke

The largest ever study of depression and anxiety is being conducted, in the hope of identifying new genes that may help explain the disorders which affect 10 million people in the UK.

One in three people will experience the symptoms of anxiety or depression in their lifetime, but the genetics causing them are poorly understood.

The two main treatments — talking therapy or anti-depressant drugs — only work for about half of sufferers.

Researchers at Kings College London (KCL) hope their work will help to solve "the big unanswered questions, and address how genes and the environment act together, and also help develop new treatment options," geneticist Dr Gerome Breen who is co-leading the study said.

In a bid to crack these questions, the Genetic Links to Anxiety and Depression (GLAD) study wants to recruit 40,000 volunteers in England who have experienced anxiety or depression.

Participants complete an online questionnaire and supply a saliva sample, from which their DNA can be extracted.

Research suggests that 30% to 40% of the risk for both depression and anxiety is genetic, the rest due to “environmental” factors, such as traumatic life experiences, family or relationship problems or poor physical health.

However, the genes which are involved in causing depression and anxiety, and how they interact with our life experiences, is unclear.

• 'It's a really exciting time in depression research':

The latest research suggests there are around 66 genetic links to depression and anxiety, and around 20 correspond to known targets for antidepressant drugs, suggesting there are many other potential genes of interest.

Researchers also say for every 1500 people studied, they find at least one new genetic variant for depression or anxiety.

By analysing both in the GLAD study, researchers hope to better tailor existing treatments for anxiety and depression, as well as identify possible new targets for drugs.

Participants will be asked to become part of the UK Mental Health Bioresource, a bank of volunteers willing to participate in future research into mental health.

• 'GLAD will revolutionise what we know about anxiety genetics':

The initiative, funded by the NHS National Institute of Health Research, is part of a wider programme to create a national resource of research participants of people, either healthy volunteers or those with a range or common or rare disorders, to investigate new links between genetics, lifestyle and disease.

“We want to hear from all different backgrounds, cultures, ethnic groups and genders, and we're especially keen to hear from young adults,” said Professor Thalia Eley, research psychologist at KCL and co-leader of the GLAD study.

“By including everyone from all parts of the population what we learn is relevant for everyone.

"This is a unique opportunity to participate in pioneering medical science."