Depression is a chronic medical illness that impacts a person's thoughts, moods and behavior. It goes beyond occasional feelings of sadness and does not imply a weakness in personality. A person cannot simply "snap out of it." Mental health professionals concur that a number of factors influence the development of depression. Hereditary factors contribute to the incidence of depression.
Variation to the 5-HTT Gene
The scientific community acknowledges the genetic link to depression as a explanation to why some forms of depression run in families. Findings of the first study connecting the genetic link to emotional stress and depression were published in the July 2003 issue of the journal "Science." A team of researchers led by Avshalom Caspi questioned why stressful situations evoke depression in some people and not in others. They found functional variations in the serotonin transporting gene, 5-HTT. Serotonin, a neurotransmitter produced in the brain, regulates mood. 5-HTT plays a critical role in controlling the function of serotonin.The researchers discovered that individuals who carry the short form of 5-HTT are more susceptible to suffer from depression after a stressful life event than individuals who carry the long form of this gene. Individuals who carry the short form of the 5-HTT gene have lower levels of serotonin.
Mutation of the Gene Coded for TPH2
According to the National Institute of Mental Health website, a mutant gene coded for the brain enzyme, TPH2, was discovered in patients who suffer from depression. TPH2 produces serotonin. Research conducted at Duke University by Dr. Marc Caron and colleagues found the mutant gene was carried by nine of the 87 patients suffering from depression, by three of the 219 control subjects and by none of the 60 patients diagnosed with bipolar disorder. Patients who carried the mutated gene responded unsuccessfully to treatment with antidepressant drugs designed to work with serotonin.
Familial Factors
Research on the correlation between heredity and depression points to familial factors. Members of a family share genetic composition, live together and imitate behavior. Individuals with immediate family members who suffer from depression have a 15 percent risk of developing depression. Individuals with no family history of depression have a 2 to 3 percent risk of developing depression. The probability of depression manifesting in one identical twin increases to 70 percent if the other twin suffers from depression. Supporting the impact of hereditary factors on depression, children whose birth parents have histories of depression but are adopted by people without histories of depression still have a 15 percent chance of suffering from depression. According to All About Depression, when one fraternal twin suffers from depression, the other twin has a 19 percent chance of developing depression. Identical twins who are raised apart have a 67 percent chance of both having depression.
