Depression

Causes

The causes of depression are not fully known. Most likely a combination of genetic, biologic, and environmental factors are at work.

Genetic Factors

Because depression runs in families, and has a strong genetic component, compelling evidence suggests that depression is a biologic phenomenon. Data from family, twin, adoption, and genetic studies have confirmed this. Studies have found that close relatives of patients with depression are two to six times more likely to develop the problem than individuals without a family history.

Biologic Factors

Evidence supports the theory that depression has a biologic basis. The basic biologic causes of depression are strongly linked to abnormalities in the delivery of certain key neurotransmitters (chemical messengers in the brain). These neurotransmitters regulate mood and associated behaviors. Scientists hope that by identifying the gene mutations that code the regulation of these neurotransmitters, they may eventually be able to predict which patients are most likely to respond to specific antidepressant drugs.

• Serotonin. Perhaps the most important neurotransmitter in depression is serotonin. Among other functions, it is important for feelings of well-being. Imbalances in the brain’s serotonin levels can trigger depression and other mood disorders.
• Other Neurotransmitters. Other neurotransmitters possibly involved in depression include acetylcholine and catecholamines, a group of neurotransmitters that consists of dopamine, norepinephrine, and epinephrine (also called adrenaline). Corticotropin-releasing factor (CRF), which is believed to be a stress hormone and a neurotransmitter, is thought to be involved in depression and anxiety. Increased CRF concentrations appear to interact with serotonin and have been detected in patients with either depression or anxiety.

The degree to which these chemical messengers are disturbed is determined by other factors, such as light, structural abnormalities in the brain, sleep disorders, or genetic susceptibility. For example, researchers have identified a defect in the gene known as SERT, which regulates serotonin and has been linked to depression.

Reproductive Hormones. In women, the female hormones estrogen and progesterone most likely play a role in depression.

Highlights
Introduction
Causes
Risk Factors
Complications
Diagnosis
Treatment
Drug Treatment Guidelines
Medications
Psychotherapy
Other Treatments
Lifestyle Changes
Resources
References

Review Date: 1/22/2009
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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