jueves, 12 de diciembre de 2019

Genes and Depression

Download PDF Copy

By Angela Betsaida B. Laguipo, BSNReviewed by Dr. Liji Thomas, MD

Depression is a common mental health condition. The World Health Organization (WHO) says depression affects about 300 million people worldwide. It’s the most common illness and the leading cause of disability across the globe. Depression affects how a person feels, think, and act. Patients with depression may have a hard time eating, sleeping, and working. Studies have linked depression to genetic predisposition.

Many people mistake depression for the mere feeling of sadness or mood fluctuations. Depression is characterized by having low mood, loss of interest, and feeling of sadness, lasting 6 to 8 months on average.

Long-lasting depression can lead to suicide. Each year, about 800,000 people with depression commit suicide, making it the second leading cause of death in people ages 15 to 29 years old.

Image Credit: TZIDO SUN / Shutterstock

What causes depression?

There are many cited possible causes of depression, though the exact cause is not fully understood. Also, the condition isn’t caused by a single source. It is due to a combination of various factors such as biological changes in the level of neurotransmitters, environmental, genetics, and psychological and social factors.

Some factors may increase the risk of developing depression. These include life events, personality, and childhood trauma. Other factors include personality, genetic factors, drug abuse, a past head injury, and chronic pain syndromes.

Role of genes in depression

A University of Edinburgh study has shown that genes play a major role in depression. The scientists have identified at least 80 genes linked to depression. In an update, the scientists identified 102 gene variants and 269 genes associated with depression.

The scientists collected and studied data from two million people in 20 countries. Genetic variations affected the nerve connections in the parts of the brain that controls personality and decision-making. The more variations there are, the higher the risk of developing depression.

Some possible genetic contributions include the role of polymorphisms in genes associated with serotonin, noradrenalin, and dopamine neurotransmission, such as variants of the.serotonin transporter genes which inhibit serotonin reuptake, leading to insufficiency of monoamines in the brain and thus predisposing to depression.

Another explanation is variation in genes that regulate the functioning of the hypothalamopituitary adrenal (HPA) axis that is activated with stress, for instance. Excessive HPA activation may contribute to depression in some people.

Another possibility is polymorphism in genes that regulate the development of the nervous system leading to fewer neurons in the adult brain.

Inflammatory conditions in the body cause the release of certain anti-inflammatory cytokines to compensate, which can act on the brain to cause depression. Genes regulating these cytokines may be involved in the onset of this condition.

Genes that regulate the circadian rhythm are another potential cause of genetic predisposition to depression by interfering with normal sleep and other body functions that depend on the circadian pacemaker. Other genes are also being studied, and some think that depression occurs across a wide spectrum of severity, various forms being only different subtypes of the same disease. This variation may depend upon the different genetic polymorphisms and their interaction with each other and with the environment.

Yet depression does not have a clear pattern of inheritance in families. Some people who have first-degree relatives with depression may have two to three times higher risk of developing the illness. But in some cases, people with family members who have depression never develop the disorder, while those who do not have a family history may develop the condition.

The serotonin link

Serotonin appears to play a pivotal role in mood balance. Serotonin is a neurotransmitter in the body that helps regular social behavior, mood, digestion, appetite, memory, sleep, and sexual function. Low serotonin levels are linked to depression.

Researchers have linked serotonin to depression. This “feel good” chemical aids in the communication between neurons in the brain. An imbalance can lead to mood disorders. Though there are many theories on the link between the two, scientists continue to wonder if serotonin may be the basis of the genetic link.

The serotonin transporter gene has received the most attention in relation to the causes of depression. Aside from the gene-related possible increase in the risk of developing depression, it may help predict antidepressant response.

Furthermore, the short version of the gene, called the 'S allele', has been linked to a heightened risk of depression, especially if the person has been through adverse childhood events. S allele has also been associated with greater mood disturbance, manifested by suicide attempts in patients.

What are the signs and symptoms of depression?

Depression is a serious illness. The signs and symptoms of depression include feelings of worthlessness, helplessness, and guilt, pessimism, fatigue, difficulty concentrating, making decisions, and remembering details, irritability, and appetite loss or overeating.

Other symptoms include restlessness, insomnia or sleeping too much, various pains (headache and cramps) that won’t go away, persistent feeling of sadness, feeling “empty”, anxiety, digestive problems, and suicidal thoughts or attempts.

Sources

World Health Organization (2018). Depression. https://www.who.int/news-room/fact-sheets/detail/depression
National Institute of Mental Health (2018).Depression. https://www.nimh.nih.gov/health/topics/depression/index.shtml
Genetics Home Reference(2019).Depression. https://ghr.nlm.nih.gov/condition/depression#inheritance
McIntosh A.M., et al., (2019). Genome-wide meta-analysis of depression identifies 102 independent variants and highlights the importance of the prefrontal brain regions. Nature Neuroscience. doi.org/10.1038/s41593-018-0326-7
Caspi A., et al., (2003). Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Science. https://doi.org/10.1126/science.1083968
Shadrina M. et al., (2018). Genetics Factors in Major Depression Disease. Frontiers in Psychiatry. https://dx.doi.org/10.3389%2Ffpsyt.2018.00334