Major Depressive Disorder Etiology

Etiology-what are the causes of MDD? Establishing the etiology of a psychological disorder is difficult. Diagnostic manuals like DSM IV-TR provide information on symptoms characteristic of a disorder, but do not outline the causes of disorders. The IB Diploma focuses on biological, cognitive and socio-cultural factors that may contribute to the onset of the disorder.

There is no simple answer Before we look at the evidence from each perspective, it is important to bear in mind that it is widely accepted that a combination of factors cause the disorder. There are important individual differences in vulnerability. It is basically not yet possible to find THE cause of depression in an individual. What do you think causes depression?

Possible causes Genetic vulnerability Neurotransmitter malfunctioning Changing hormones Life events: death, divorce, accidents/trauma. Stress: money problems, threat of violence, difficulties at work, exams Individual differences: childhood experiences, coping skills, cognitive style, level of social support Lifestyle: being obese, misuse of alcohol and drugs

The biological level of analysis These include: Genetic factors Biochemical factors-neurotransmitters and hormones.

Genetic factors: twin studies Twin Studies-these studies are used to establish a genetic cause. Monozygotic twins-one egg or identical Dizygotic twins-two eggs or fraternal Average number of genes shared by blood relatives MZ twins share 100% of their genetic information DZ twins share 50% of their genetic information (as do parents and siblings)

Genetic factors: twin studies Twin studies measure the degree of similarity or concordance of characteristics (such as being diagnosed with Major depressive disorder) between twins. It is expressed as a %. The assumption is that if there is a higher concordance rate between MZ twins, than between DZ twins, then the cause is likely to be genetic. Comparing concordance rates of MZ and DZ twins is valuable because the twins are born at the same time and share the same environment.

Genetic factors: Family studies If Major depressive disorder runs in families it suggests a genetic component. The closer the relationship the more likely people are to share a diagnosis. 100%-MZ twin 50%-DZ twin 50%-parent, sibling 25%-aunt, uncle, niece, nephew

Genetic factors: Adoption studies Adoption studies help to control for similar environments that related individuals are likely to share. If there are high concordance rates for MZ twins who are raised in different families then the genetic evidence is strong.

Identifying a gene Linkage studies Attempt to identify sequences of genes that appear to be inherited along with a predisposition to develop depression.

Biochemical factors: Neurotransmitters Neurons or nerve cells transmit information within the brain and around the body. One neuron can be connected to thousands of other neurons. Between each neuron (dendrite and terminal end bulb) there are gaps. Chemicals called neurotransmitters cross the gaps (between the pre and post synaptic membranes) and pass on the information.

Biochemical factors: Neurotransmitters There are receptor sites on the post synaptic membrane. The neurotransmitters either excite or inhibit the next neuron. Neurotransmitters are then broken down and re- absorbed by the end bulb-this is a process called re-uptake.

Biochemical factors: Hormones Endocrine glands secrete hormones into the blood stream to affect behaviour. Cortisol, which is a stress hormone has been linked with depression. It is released by the adrenal glands but controlled by the pituitary gland.