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Cause of bipolar disorder:
Biological and Hereditary Aspects
 It has also been
hypothesized that the cause of bipolar disorder may be related to
either ion activity or hereditary components.
Ion activity as a possible cause of bipolar disorder:
On both sides of
the cell membrane of neurons are positively charged sodium ions. It
is hypothesized that they may be a cause of bipolar disorder in that
they send incoming messages down and around to the nerve endings. It
is believed that when the neuron is at rest, most of the sodium ions
sit on the outside of the membrane. When an incoming message
stimulates the neuron at its receptors site, the sodium ions on the
outside of the membrane travel across to the inside. This may start a
wave of electrochemical activity that continues down the length of the
neuron resulting in a "firing". A flow of potassium ions from the
inside to the outside will then help it to return to its original
resting state.
Ions must travel
properly back-and-forth between the outside and inside of the neural
membrane in order for brain messages to be sent and received
properly. Some theorists believe that the improper transportation
of the ions may cause neurons to fire much too easily (resulting in
mania) or to resist firing too much (resulting depression). These
problems of transportation of the ions will produce shifting
misalignments along neural membranes and consequent fluctuations of
mood from one extreme to the other. In support of this theory of ions
as a potential cause of bipolar disorder, investigators have found
membrane defects in the neurons of persons with bipolar disorders and
have observed abnormal functioning in the proteins that help with this
transportation system across the membranes of the neuron.
Genetic factors as the cause of bipolar disorder:
There are many
experts that believe the cause of bipolar disorder is related to
biological predisposition. Findings from family pedigree studies
have provided some support for this idea. It has been found that
identical twins of persons with bipolar disorder have a 40% likelihood
of also developing this disorder and fraternal twins, siblings and
other close relatives of such persons have a 5% to 10% likelihood,
compared with the usual 1% prevalence rate in the general population.
Researchers into
the cause of bipolar disorder have also conducted genetic linkage
studies in order to identify possible patterns related to the
inheritance of this disorder. These studies usually select large
families that have high rates of disorder over several generations and
observe the distribution patterns of disorder among family members,
and try to figure out whether it closely follows the distribution
pattern of a known genetically transmitted family trait (called a
genetic marker ) such as red hair, color blindness or a particular
medical condition.
Researchers into
the cause of bipolar disorder have studied the records of Belgium,
Israeli and Italian families that have high rates of bipolar disorder
across several generations. One team of researchers have seemed to
link bipolar disorder to genes on the X-chromosome. Other research
teams however, later using techniques from molecular biology to
examine genetic patterns of large families, stated that they link
bipolar disorder to genes on chromosome's 4, 6, 11, 12, 13, 15, 18 and
22. Such diversity of results may mean that the logic behind the
various gene studies is flawed. Alternatively, other researchers have
concluded that the cause of bipolar disorders may be related to
genetic abnormalities that combine to bring about this condition.
Information from Abnormal Psychology Fourth Edition by Ronald
Comer
Additional information and
webpage by
Paul Susic MA Licensed Psychologist Ph.D Candidate (Health
Psychology
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