Biological (genetic) causes of depression

Depression and genetic predisposition

Depression is not only a medical but also a social problem. This is the most expensive disease that bears a heavy burden on the patient, relatives, and society as a whole. Depression is one of the most common diseases in the world. Patients with depression often go to general practitioners rather than psychiatrists and psychologists, resulting in ineffective treatment, complications and disability.

One of the causes of depression is a genetic predisposition, which is manifested not only by signs of depression among relatives, but also by psychosomatic diseases:

  • hypertension;
  • thyroid disease (hyperthyroidism);
  • peptic ulcer;
  • bronchial asthma.

Genetic predisposition to depression is an established fact that can lead to the development of new methods of diagnosis and treatment, up to intervention in the genome of the human embryo.

Depression gene and bipolar disorder gene

In 1980, a gene located on chromosome 11 was identified that is associated not only with the development of depression, but also with bipolar disorder (or manic-depressive psychosis).

Later, geneticists found that genes on chromosome 4 and on the X chromosome cause depression. With deletions and duplications of these genes, an increase in sensitivity to stress occurs, which leads to the development of depression.

Practitioners have found that if one of the family members has suffered at least one depressive episode, then the risk of depression in other relatives doubles. And relatives of people with bipolar disorder have a sixfold increase in the risk of depression. The genetic predisposition is confirmed by the fact that in the presence of bipolar disorder in both parents, depression in children is observed in 75% of cases.

Tryptophan hydroxylase gene and depression

Decreased production of serotonin in the brain leads to depression. Tryptophan hydroxylase is an enzyme involved in the synthesis of serotonin in various structures of the cerebral cortex.

It is encoded by the TPH2 gene located on chromosome 12 on the q arm. Polymorphism in this gene, caused by the mutation, leads to a decrease in serotonin production by 80%. Besides depression, changes in this gene can lead to suicidal tendencies.

Brain trophic factor gene and depression

The level of brain neurotrophic factor (BDNF) is reduced in chronic stress, which has been proven in animal studies. This factor is involved in neurogenesis and the development of major depressive disorder.

Various variations in the brain trophic factor gene affect a person’s vulnerability to depression. Indirect evidence of this effect is that taking antidepressants increases the level of BDNF in the hippocampus and increases resistance to stress.

Serotonin transporter gene and depression.

The genetic predisposition to depression may be related to defects in serotonin-transporting proteins. Proteins associated with serotonin have recently been intensively studied, as they are targets of antidepressant drugs.

Some of them can serve as a biomarker of the patient’s expected response to treatment with a particular antidepressant drug. A total of 12 candidate genes have been identified that can predict the effectiveness of treatment for depression.

The discovery of genes responsible for the development of depression does not diminish the importance of environmental factors in the development of the disease. Biological background – a combination of genes, the level of neurotransmitters , hormones, and other biologically active substances is responsible for a person’s response to traumatic factors leading to depression. Moreover, there are mechanisms by which environmental factors can influence the genes responsible for the development of depression. This holds great promise in the treatment of depression.

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