A primary type of depression is Major Depressive Disorder (MDD). Major Depressive Disorder is genetic – there is a possibility that other family members of someone suffering from MDD may have MDD too.

The role of genes and serotonin in MDD
Brain cells, known as neurons, communicate between themselves through chemical substances that are known as neurotransmitters. These neurotransmitters travel between brain cells. Serotonin, which is a type of neurotransmitter, is attributed to the manifestations of Major Depressive Disorder. Low levels of serotonin, clubbed with a genetic predisposition of MDD may cause Major

Depressive Disorder.
Genes decrease or increase the levels of serotonin. Genes can also affect the velocity of the neuron signals that travel between neurons. Normal neuronal speeds help us deal with and properly respond to environmental stressors. If these neuronal speeds are not in the required range, then Major Depressive Disorder may be manifested when there is exposure to some kind of environmental stress.

The role of norepinephrine in MDD
Norepinephrine is another type of neurotransmitter that may be associated with causing MDD. A certain set of symptoms of Major Depressive Disorder are known as the positive effect. The clinical symptoms that are categorized in this particular set are:

• A loss of interest
• A loss of energy
• A loss of pleasure
• Fatigue
• These symptoms improve when the brain’s level of norepinephrine is normal and these symptoms manifest when the brain’s level of norepinephrine is low.
• The role of dopamine in MDD
• The third type of neurotransmitter that may be associated with causing MDD is dopamine. Research shows that decreased dopaminergic neurotransmission may cause Major Depressive
• Disorder. The following are some of the dopamine-related symptoms of MDD:
• Impaired motivation
• Weakened concentration
• Diminished pleasure

Dopamine plays a significant role in mood modulation. In some cases, dopamine-related symptoms and disturbances may be relieved by antidepressants.
Other factors for MDD:

• The other factors that may trigger or cause Major Depressive Disorder are:
• Hormonal Imbalance
• Medical conditions (like hypothyroidism and cancer)
• Medications (like steroids)