Historically, mood disorders have been blamed upon evil spirits, possession and witchcraft. More modern investigations have looked at environmental causes and childhood experiences. However, more and more evidence shows that genetics play an important role in these disorders, including bipolar disorder.
A large study involving multiple universities across the country, including Hopkins, has uncovered a significant association between a gene for brain-derived neurotrophic factor (BDNF) and bipolar disorder.
American Caucasian families with members affected by bipolar disorder were recruited at 10 research centers throughout the country, including the Hopkins School of Medicine.
A total of 1,749 people from 250 families participated in the study. Affected individuals and their healthy family members were studied.
In the affected group, researchers found 10 single nucleotide polymorphisms (SNPs), or differences of just one of the letters that make up the genetic code, in the BDNF gene. The data suggested that several of the SNPs were associated with bipolar disorder in the subject.
"Certain variants in these polymorphisms were passed on from parents to offspring with bipolar disorder more than we would expect by chance alone," Associate Professor at the Bloomberg School of Public Health Peter Zandi said.
"Such an association is evidence that?variation in?BDNF may be responsible for increasing the risk of bipolar disorder, but it does not prove it."?
Two of the alleles, or variants, that the study focused on were located in a region of the human BDNF gene that is highly conserved among other vertebrates, which suggests that section of the BDNF protein has a significant functional role.
BDNF protein is important in the growth and survival of peripheral and central neurons in adults. It is fairly well-studied and evidence already exists implicating the protein in mood-related disorders, including bipolar disorder. Researchers have studied the impact of BDNF - both the protein and the gene that codes for it - on memory, schizophrenia, obesity, aging and bulimia.
Previous studies showed that people with bipolar disorder had lower levels of BDNF expression. An injection of BDNF worked like an antidepressant on rats and it is thought that the gene protects our neurons against stress-related damage.
"Several previous studies have suggested that variation in the gene BDNF may be associated with?susceptibility for developing bipolar disorder," Zandi said. "However, the findings are not entirely consistent."
Bipolar disorder was formerly referred to as manic-depressive disorder. It is classically characterized by cycling between major depressive episodes and manic episodes where the person experiences increased energy.
However, there are many variations in the length and severity of the episodes, from person to person and in a single person over time. The first major mood episode usually occurs around 20 years of age but can happen even into the 30s.
Although this study suggests a relationship between the BDNF gene and bipolar disorder, the data does not show conclusively that genetic variation causes the illness. It may be one of many risk factors.
"It is premature to suggest that testing of?the BDNF gene in families is important to determine one's risk of developing bipolar disorder," Zandi said.
"Further study is required to?demonstrate a causal relationship between the variation in this gene and risk of?bipolar disorder."
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