If you have depression, you feel sad most of the day, for weeks at a time. Your sadness affects your performance at work, relationships with your friends and family, and even the things you used to love.

Depression overlaps with ADHD in two distinct ways: as a separate, unique condition occurring on its own, and as a secondary condition triggered by the frustrations of living with ADHD.

International scientists have identified 44 genetic variants that can increase the risk of developing major depression and found that all humans carry at least some of them

In the largest study, scientists found that the genetic basis for depression is shared with other psychiatric disorders such as schizophrenia and that a number of the variants are linked to the targets of antidepressant drugs.

Major depression affects around 14 percent of people worldwide and is the biggest contributor to long-term disability in the general population. Yet only about half of patients respond well to existing treatments.

The new genetic variants discovered have the potential to revitalize depression treatment by opening up avenues for the discovery of new and improved therapies,” said Gerome Breen of King’s College London, who worked on the research team.

The study – published on Thursday in the journal Nature Genetics – was a global effort, with data covering more than 135,000 patients with major depression and around 344,000 controls as comparisons.

“This study has shed a bright light on the genetic basis of depression, but it is only the first step,” said Cathryn Lewis, another King’s College London expert who worked on the team.

“We need further research to uncover more of the genetic underpinnings, and to understand how genetics and environmental stressors work together to increase risk of depression.”

With this study, depression genetics has advanced to the forefront of genetic discovery,’ says Dr Breen from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London.

‘The new genetic variants discovered have the potential to revitalise depression treatment by opening up avenues for the discovery of new and improved therapies.”

Major depression affects approximately 14% of the global population and is the biggest contributor to long term disability in the general population worldwide. Yet only about half of patients respond well to existing treatments.

Depression is an incredibly common disorder that affects millions of people in the UK,’ says Professor Lewis of the IoPPN, who is leading efforts to conduct even larger international studies.

In the UK, the work was partly-funded by the National Institute for Health Research (NIHR) Biomedical Research Centre at South London and Maudsley NHS Foundation Trust and King’s College London, and the Medical Research Council.

The study also found that all humans carry at least some of the 44 genetic risk factors linked to major depression

Previous studies had also identified some genetic links to depression, but researchers say this is the most comprehensive analysis so far, and could help in the development of more targeted medications to treat depression.

The latest study is being described as “an unprecedented global effort,” involving more than 200 scientists and data from more than 135,000 people with major depression. The study also used data from 344,000 mentally healthy individuals as control subjects. According to the Mood Disorders Society of Canada, about one in 10 Canadians will experience an episode of major depressive disorder during their lifetime.

9 Most Common Causes of Depression

Common Causes of Depression

Common Causes of Depression

Genetics and Biology

Twin, adoption, and family studies have linked depression to genetics. While studies suggest that there is a strong genetic component, researchers are not yet certain about all the genetic risk factors for depression

Brain Chemistry Imbalance

Depression is believed to be caused by an imbalance in the neurotransmitters which are involved in mood regulation.2

Neurotransmitters are chemical substances which help different areas of the brain communicate with each other. When certain neurotransmitters are in short supply, this may lead to the symptoms we recognise as clinical depression.

Female Sex Hormones

It has been widely documented that women suffer from major depression about twice as often as men. Because of the incidence of depressive disorders peaks during women’s reproductive years, it is believed that hormonal risk factors may be to blame.

Brain Chemistry Imbalance

Depression is believed to be caused by an imbalance in the neurotransmitters which are involved in mood regulation.2

Neurotransmitters are chemical substances which help different areas of the brain communicate with each other. When certain neurotransmitters are in short supply, this may lead to the symptoms we recognise as clinical depression.

Female Sex Hormones

It has been widely documented that women suffer from major depressionabout twice as often as men. Because of the incidence of depressive disorders peaks during women’s reproductive years, it is believed that hormonal risk factors may be to blame.

Circadian Rhythm Disturbance

One type of depression, called seasonal affective disorder (officially known as major depressive disorder with seasonal pattern) is believed to be caused by a disturbance in the normal circadian rhythm of the body. Light entering the eye influences this rhythm, and, during the shorter days of winter, when people may spend limited time outdoors, this rhythm may become disrupted.

Poor Nutrition

A poor diet can contribute to depression in several ways. A variety of vitamin and mineral deficiencies are known to cause symptoms of depression

Physical Health Problems

The mind and the body are clearly linked. If you are experiencing a physical health problem you may discover changes in your mental health as well.  Illness is related to depression in two ways. The stress of having a chronic illness may trigger an episode of major depression. In addition, certain illnesses, such as thyroid disorders, Addison’s disease, and liver disease, can cause depression symptoms.

Drugs

Drugs and alcohol can contribute to depressive disorders.7 But, even some prescription drugs have been linked to depression. Some drugs that have been found to be associated with depression include anticonvulsants, statins, stimulants, benzodiazepines, corticosteroids, and beta-blockers.

Stressful Life Events

Stressful life events, which overwhelm a person’s ability to cope, may be a cause of depression. Researchers suspect high levels of the hormone cortisol, which are secreted during periods of stress, may affect the neurotransmitter serotonin and contribute to depression.

Grief and Loss

Following the loss of a loved one, grieving individuals experience many of the same symptoms of depression. Trouble sleeping, poor appetite, and a loss of pleasure or interest in activities are a normal response to loss.