Psychiatry is not an exact science. Other than a very rough idea of the chemicals in the brain (neurotransmitters) which may be associated with mental illness, we have no objective understanding of the factors which lead to mental illness. For example, we know that the neurotransmitters serotonin, norepinephrine, and dopamine seem to have an effect on mood, and that abnormalities in the levels of these chemicals in certain areas of the brain may lead to mood disorders. Beyond that, we know very little.
Why is it that different people experience different symptoms when they are depressed? Why do some people sleep too much while others sleep too little? Why do some folks have increased appetite while others have reduced appetite. Why do some people have a lot of anxiety when they are depressed while others don't.
Why might a person respond to one medication in a specific antidepressant class and not respond to another in the same class. As a psychiatrist, I see people who respond very well to sertraline, but if the medication is changed for some reason, they don't respond as well or even at all to paroxetine. Sertraline (Zoloft) and paroxetine (Paxil, Pexeva) are both selective serotonin reuptake inhibitors (SSRIs). These medications seem to work by increasing the amount of serotonin surrounding specific nerve cells (neurons) in the brain. Serotonin may help improve mood by interacting with proteins (receptors) on the outside of the neuron.They do this by preventing the uptake of the serotonin back into the neuron so that there is more available to be used by the outside of the cell. Since sertraline and paroxetine are both block the reuptake of serotonin, why wouldn't a person respond similarly to either medication?
Recently advances in genetic research are revealing how very complex the causes of mental illness may be.
From Goldberg, 10/14/08, Boston Globe
"Dr. Thomas Insel, director of the National Institute of Mental
Health, compares psychiatric genetics to a 1,000-piece jigsaw puzzle,
in which researchers have just started to fit together a few edge
pieces.
But "this is unprecedented progress," he said. "This is a
time of real excitement in a field that up until now hasn't given us
much to cheer about."
The findings, including major work
published by Boston-area scientists, suggest that although mental
illness is known to run in families, it may sometimes stem not from
inherited defects but from spontaneous mutations that occur during
earliest development in the womb.
Researchers are also finding
some apparent genetic links between dramatically different disorders.
For example, a genetic glitch previously shown to raise the risk of
schizophrenia is also linked to autism and mental retardation, a study
in the New England Journal of Medicine reported last month (NEJM Sept).
Dr.
Edward Scolnick, director of the Broad Institute's Stanley Center for
Psychiatric Resarch in Cambridge, has found himself telling people of
late that the field of psychiatric genetics has "crossed the
Mississippi."
"To explore the West, it will take a lot of work,
and a lot of money," he said, arguing that the field needs an
additional $200 million or more to quickly unravel the basic "genetic
architecture" of severe mental illness. "There is a lot left to do. But
we know how to go about it now."
This is an exciting time to be a psychiatrist. I believe that after centuries of blindly searching for answers to the causes of mental illness, we have finally started unraveling the mystery.