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This means that nearly one in five Americans will meet the criteria for MDD during their lifetime.

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The month prevalence—the proportion of people who meet criteria for a disorder during a month period—for PDD is approximately 0. Although the onset of MDD can occur at any time throughout the lifespan, the average age of onset is mids, with the age of onset decreasing with people born more recently APA, The duration of MDEs varies widely. An earlier age of onset predicts a worse course. The lifetime prevalence rate of bipolar spectrum disorders in the general U. Prevalence estimates, however, are highly dependent on the diagnostic procedures used e.

BD often co-occurs with other psychiatric disorders. The co-occurrence of BD with other psychiatric disorders is associated with poorer illness course, including higher rates of suicidality Leverich et al.

Mood Disorders | Noba

A recent cross-national study sample of more than 60, adults from 11 countries, estimated the worldwide prevalence of BD at 2. In this study, the prevalence of BD varied somewhat by country.

Whereas the United States had the highest lifetime prevalence 4. Variation in prevalence rates was not necessarily related to SES, as in the case of Japan, a high-income country with a very low prevalence rate of BD 0. With regard to ethnicity, data from studies not confounded by SES or inaccuracies in diagnosis are limited, but available reports suggest rates of BD among European Americans are similar to those found among African Americans Blazer et al.

Another large community-based study found that although prevalence rates of mood disorders were similar across ethnic groups, Hispanic Americans and African Americans with a mood disorder were more likely to remain persistently ill than European Americans Breslau et al. Misdiagnosis of BD can result in the underutilization of treatment or the utilization of inappropriate treatment, and thus profoundly impact the course of illness.

As with MDD, adolescence is known to be a significant risk period for BD; mood symptoms start by adolescence in roughly half of BD cases Leverich et al. Longitudinal studies show that those diagnosed with BD prior to adulthood experience a more pernicious course of illness relative to those with adult onset, including more episode recurrence, higher rates of suicidality, and profound social, occupational, and economic repercussions e. Mood disorders are complex disorders resulting from multiple factors. Causal explanations can be attempted at various levels, including biological and psychosocial levels.

Below are several of the key factors that contribute to onset and course of mood disorders are highlighted. Research across family and twin studies has provided support that genetic factors are implicated in the development of MDD. Twin studies suggest that familial influence on MDD is mostly due to genetic effects and that individual-specific environmental effects e.

The mode of inheritance is not fully understood although no single genetic variation has been found to increase the risk of MDD significantly. Instead, several genetic variants and environmental factors most likely contribute to the risk for MDD Lohoff, One environmental stressor that has received much support in relation to MDD is stressful life events.


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In particular, severe stressful life events—those that have long-term consequences and involve loss of a significant relationship e. Depression research has not been limited to examining reactivity to stressful life events.


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Much research, particularly brain imagining research using functional magnetic resonance imaging fMRI , has centered on examining neural circuitry—the interconnections that allow multiple brain regions to perceive, generate, and encode information in concert. A meta-analysis of neuroimaging studies showed that when viewing negative stimuli e. Other environmental factors related to increased risk for MDD include experiencing early adversity e.

For example, marital dissatisfaction predicts increases in depressive symptoms in both men and women. Research has found that people with MDD generate some of their interpersonal stress Hammen, People with a pessimistic attributional style tend to make internal versus external , global versus specific , and stable versus unstable attributions to negative events, serving as a vulnerability to developing MDD.

For example, someone who when he fails an exam thinks that it was his fault internal , that he is stupid global , and that he will always do poorly stable has a pessimistic attribution style. Although there have been important advances in research on the etiology, course, and treatment of BD, there remains a need to understand the mechanisms that contribute to episode onset and relapse. It may be argued that a high rate of heritability demonstrates that BD is fundamentally a biological phenomenon.

However, there is much variability in the course of BD both within a person across time and across people Johnson, The triggers that determine how and when this genetic vulnerability is expressed are not yet understood; however, there is evidence to suggest that psychosocial triggers may play an important role in BD risk e.

In addition to the genetic contribution, biological explanations of BD have also focused on brain function. Many of the studies using fMRI techniques to characterize BD have focused on the processing of emotional stimuli based on the idea that BD is fundamentally a disorder of emotion APA, Findings show that regions of the brain thought to be involved in emotional processing and regulation are activated differently in people with BD relative to healthy controls e. However, there is little consensus as to whether a particular brain region becomes more or less active in response to an emotional stimulus among people with BD compared with healthy controls.

Mixed findings are in part due to samples consisting of participants who are at various phases of illness at the time of testing manic, depressed, inter-episode. Sample sizes tend to be relatively small, making comparisons between subgroups difficult. Additionally, the use of a standardized stimulus e. Within the psychosocial level, research has focused on the environmental contributors to BD. A series of studies show that environmental stressors, particularly severe stressors e. Interestingly, positive life events can also adversely impact the course of BD.

People with BD suffer more manic symptoms after life events involving attainment of a desired goal Johnson et al. Such findings suggest that people with BD may have a hypersensitivity to rewards. Evidence from the life stress literature has also suggested that people with mood disorders may have a circadian vulnerability that renders them sensitive to stressors that disrupt their sleep or rhythms.

Consistent with this theory, studies have shown that life events that involve a disruption in sleep and daily routines, such as overnight travel, can increase bipolar symptoms in people with BD Malkoff-Schwartz et al. There are many treatment options available for people with MDD. First, a number of antidepressant medications are available, all of which target one or more of the neurotransmitters implicated in depression. The earliest antidepressant medications were monoamine oxidase inhibitors MAOIs.

Mood Disorders Across the Lifespan

MAOIs inhibit monoamine oxidase, an enzyme involved in deactivating dopamine, norepinephrine, and serotonin. Although effective in treating depression, MAOIs can have serious side effects. Patients taking MAOIs may develop dangerously high blood pressure if they take certain drugs e. Tricyclics, the second-oldest class of antidepressant medications, block the reabsorption of norepinephrine, serotonin, or dopamine at synapses, resulting in their increased availability.

Tricyclics are most effective for treating vegetative and somatic symptoms of depression. Like MAOIs, they have serious side effects, the most concerning of which is being cardiotoxic. Selective serotonin reuptake inhibitors SSRIs; e. SSRIs, the most commonly prescribed antidepressant medication, block the reabsorption of serotonin, whereas SNRIs block the reabsorption of serotonin and norepinephrine.

In particular, they are less cardiotoxic, less lethal in overdose, and produce fewer cognitive impairments. They are not, however, without their own side effects, which include but are not limited to difficulty having orgasms, gastrointestinal issues, and insomnia.

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Other biological treatments for people with depression include electroconvulsive therapy ECT , transcranial magnetic stimulation TMS , and deep brain stimulation. ECT involves inducing a seizure after a patient takes muscle relaxants and is under general anesthesia. ECT is viable treatment for patients with severe depression or who show resistance to antidepressants although the mechanisms through which it works remain unknown. Repetitive TMS is a noninvasive technique administered while a patient is awake. Brief pulsating magnetic fields are delivered to the cortex, inducing electrical activity.

Although the onset of MDD can occur at any time throughout the lifespan, the average age of onset is mids, with the age of onset decreasing with people born more recently APA, The duration of MDEs varies widely.

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Causes of Bipolar Disorder

An earlier age of onset predicts a worse course. The lifetime prevalence rate of bipolar spectrum disorders in the general U. Prevalence estimates, however, are highly dependent on the diagnostic procedures used e. BD often co-occurs with other psychiatric disorders. The co-occurrence of BD with other psychiatric disorders is associated with poorer illness course, including higher rates of suicidality Leverich et al. A recent cross-national study sample of more than 60, adults from 11 countries, estimated the worldwide prevalence of BD at 2.

In this study, the prevalence of BD varied somewhat by country.