The evidence in this study consistently shows that the influence of genetic factors is around 30- 40% therefore the predisposition to develop depression can be inherited. The remaining 60-70% are individual- specific environmental effects. These effects are usually related to adverse events in childhood or recent stress due to interpersonal adversities. Depression usually occurs as a result of life stressors interacting with heritable genetic and personality vulnerabilities. These produce both psychological and physiological dysfunction. The continued exposure to stress produces characteristic "alterations in the major chemical messenger systems responsible for neuronal transmission namely serotonin, norepinephrine and dopamine"" (Friedman and Anderson, 2010). Zenker (Neurotransmitters and Depression, n.d.) explained that "serotonin is known to be the calming and inhibiting neurotransmitter while dopamine usually regulates the sense of pleasure, satisfaction and reward. However, norepinephrine affects one's motivation, ability to focus and energy." As a result of this, the monoamine- deficiency hypothesis was formulated which states that, "the underlying pathophysiological basis of depression is a depletion of the neurotransmitters: serotonin, dopamine or norepinephrine in the central nervous system"" (World Psychiatry, 2010). It is imperative that one remembers that there is no single cause for depression; rather, it is a combination of stress and a person's vulnerability to developing depression. .
Signs and Symptoms of Depression.
Depression can change or distort the way you see yourself, your life and those around you. With depression you often see everything in a negative way. However, people with depressive illnesses do not all experience the same symptoms. The severity, frequency and duration of symptoms vary depending on the individual and their particular illness. "Depression is characterized by symptoms that usually fall into two categories: psychosocial and somatic"" (Friedman, 2010).
