Genetics
of Bipolar Disorder: A Hereditary Mental Illness?
Is Manic Depression an
Inherited Psychological Disorder that Runs in Families?
Early research on the genetics of bipolar
disorder
relied on twin studies and examination of inheritance patterns among
family members. Now that the human genome has been decoded, science is
getting closer to identifying all of the specific genes
involved in the development of this mood disorder.
Inheritance Patterns of Bipolar Disorder
Family
studies of inheritance patterns, as well as twin and adoption studies
of those with bipolar disorder, have revealed that first-degree
relatives of affected individuals have a higher risk of developing
bipolar symptoms. Still, a child of a bipolar and a nonbipolar parent
have less than a 15% chance of developing the disorder, although those
odds may increase if there are others in the family who have a mood
disorder.
Studies of identical twins
have shown that if one twin is bipolar, the other has at least an 85%
chance of developing the disorder. Twins certainly share many of the
same environmental factors as well, both in utero and throughout
childhood, but shared experience does not account for the extremely
high likelihood that genetically predisposed twins will share the
disorder.
So it is established that bipolar
disorder
tends to run in families. But now, with the human genome mapped,
scientists are starting to pinpoint the actual genes that are linked to
the disorder.
The Complex Genetics of Bipolar
Disorder
Within
the last few years, researchers have identified several genes that
appear to be associated with the disorder. Because a number of genes
are involved in development of bipolar illness, the inheritance
patterns are not straightforward, as indicated by the fact that
children of a bipolar parent have a relatively small risk of developing
the disorder. All those who may have a genetic predisposition don't
necessarily ever end up developing bipolar symptoms.
The
involvement of several genes, suggests that a range of biochemical
problems can occur in people who possess a genetic predisposition for
bipolar disorder, and that perhaps, the specific type, and number, of
genetic abnormalities contribute to how the disorder manifests in an
individual.
Is Manic Depression an
Inherited Psychological Disorder that Runs in Families?
The Human Genome Project
Our
understanding of genetic disorders has exploded since the completion of
Human Genome Project (HGP) in 2003. This 13-year project was launched
cooperatively by the U.S. Department of Energy and the National
Institutes of Health, and participated in by researchers from all over
the world.
The Human
Genome Project had several Herculean objectives. It identified all of
the genes in the of human DNA, determined the sequences of the 3
billion chemical base pairs that make up the "genetic code", stored the
information in databases, and developed data analysis tools and
technologies so that the information could be used to learn more about
genetic disorders.
Completion of the Human Genome Project now
enables scientists to learn more about genetic disorders by comparing
the genome (all the DNA) of individuals that have a certain disease
with the human genetic code deciphered by the Genome Project. If there
are, for example, consistent abnormalities certain segments of DNA of
those with bipolar disorder, it would suggest that those are areas of
DNA that may be involved with development of the disorder.
Genes Involved in the Development of Bipolar Disorder
Research
that has taken place since the human genome was decoded, has already
revealed much about the specific genes that contribute to bipolar
disorder. Two different variations of a gene called Ankyrin 3 (ANK3),
on chromosome 10, have each been found to pose independent genetic risk
factors for bipolar disorder. In addition, variation in a gene,
CACNA1C, on chromosome 12, also appears to be involved. Molecular
genetic studies have also found information on chromosomes 12, 14, and
15 that relates to the age of onset for bipolar disorder.
Abnormalities in the GABA-A receptor genes, scattered over several
chromosomes, seem to be present both in those with bipolar disorder
and also in people with schizophrenia. GABA receptors are a type of
neurological receptor that responds to the neurotransmitter
gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter of
the central nervous system.
Is Manic Depression an
Inherited Psychological Disorder that Runs in Families?
With
the huge expansion of knowledge in the area of molecular genetics, we
may soon be able to understand exactly what causes bipolar disorder,
how the disorder differs between individuals, and why there are
variations in the age of onset. And this is not just an academic
pursuit. Knowing exactly what is
contributing to a persons' bipolar experience may allow for very
specific use of pharmaceuticals and other treatments that could
effectively treat those with bipolar disorder on an individual basis.
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