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schizophrenia
AetiologyAsschizophrenia is a complex brain disorder, it likely
results from the interplay of genetic,behavioural, developmental
and other factors. The exact cause of this group of illnesses is
not
known but stress, trauma and viral infection at an early age are
factors thought to be involved.
Schizophrenia can run in families and it is likely that the
disease has a genetic component ifone twin of an identical pair has
schizophrenia, there is a 46% chance that the other twin willalso
suffer from a schizophrenic disorder. It is not known how many
genes are involved or howthe genetic predisposition is transmitted.
In addition, recent evidence suggests that schizophrenia
may result when neurons in the brain form inappropriate
connections during foetaldevelopment. It may be that an
intrauterine starvation or infection causes such
inappropriateconnections to form and these may lie dormant until
puberty when substantial neuronreorganisation occurs in the brain.
Identification of specific genes involved in the development
ofschizophrenia will provide important clues as to what goes wrong
in the brains of people with the
disease and this will guide the development of improved
treatments.Stress imposed by life events or family circumstances
appears to be an important external eventassociated with
schizophrenia. The onset of illness is often associated with a
distressful period inlife and it may be that stress can trigger the
onset of illness in those people with a geneticpredisposition to
the disease.
An imbalance in the concentrations of dopaminergic and
glutamatergicsystems in the brain isalso thought to play a role in
the development of schizophrenia. The dopamine hypothesis
statesthat the behavioural patterns typical of schizophrenia are a
result of overactivity of dopamine incertain regions of the brain.
Serotonin is also important in schizophrenia and it may be that
theserotonin system interacts with the dopamine system to modify
the way in which it operates. Theserotonin receptors which are
important in the treatment of schizophrenia are 5-HT1, 5-HT2
and
5-HT3.What Happens in the Brain?
The areas of the brain implicated in schizophrenia are
theforebrain ,hindbrain and limbic
system .
It is thought that schizophrenia may be caused by a disruption
in some of the functional circuitsin the brain, rather than a
single abnormality in one part of the brain. Although the brain
areasinvolved in this circuit have not been defined, thefrontal
lobe,temporal lobe, limbic system,
(specifically the cingulate gyrus , the amygdala and the
hippocampus ) and the thalamus
are thought to be involved. The cerebellum , which forms part of
the hindbrain, also appears tobe affected in people with
schizophrenia.
neurotransmitters are implicated in the development of
schizophrenia. The dopaminehypothesis of schizophrenia postulates
that schizophrenia is caused by an overactive dopaminesystem in the
brain; excessive dopamine and reduced striatal activity can disrupt
all aspects ofmotor, cognitiveand emotional functioning and can
result in an acute schizophrenicpsychosis.An excessive dopamine
concentration in the brain of people with a schizophrenic disorder
wasoriginally thought to be associated with increased activity of
the D2 class of dopamine receptors
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in theprefrontal cortex . Recent studies indicate that reduced
numbers of the D1 class ofdopamine receptors may contribute to the
rise in dopamine concentration. Otherneurotransmitters, including
serotonin, glutamate, gamma aminobutyric acid and acetylcholinemay
also be involved in the pathogenesis of schizophrenia. It may be
that due to the carefulorchestration
betweenneurotransmittersystems, an imbalance in one
neurotransmitter affects
others which are not causally involved in the pathogenesis of
disease.Several structural changes are found in the brains of
people with schizophrenia, most of which
occur in the forebrain. Reductions in the volume ofgrey matter
in the frontal lobe, anddecreased brain volume and activity, have
been repeatedly noted among people with a
schizophrenic disorder. Theventricles are commonly found to be
larger than normal, as are the
basal nuclei , while the hippocampus and amygdala are often
smaller. The disease is alsoassociated with alterations in blood
flow to certain areas of the brain.
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