Category: Bipolar Disorder

One of the biggest challenges in psychiatric genetics has been to replicate findings across large studies.

Scientists at King's College London, Institute of Psychiatry have now performed one of the largest ever genetic replication studies of bipolar affective disorder, with 28,000 subjects recruited from 36 different research centers. Their findings provide compelling evidence that the chromosome 3p21.1 locus contains a common genetic risk for bipolar disorder, the PBRM1 gene.

The locus at 3p21.1 has also been previously associated with depression and schizophrenia. Using a separate dataset of over 34,000 subjects, they did not confirm association of this same variant with schizophrenia.

Thus, they replicated the association of the marker with bipolar disorder, but not with schizophrenia. This is an interesting finding, in that it distinguishes the heritable risk for bipolar disorder and schizophrenia. It contrasts with the majority of studies that have found that schizophrenia risk genes also contribute to the risk for bipolar disorder.

"This study adds to the recent rapid progress in identifying genes for mental illness. The last few years have seen the identification of about two dozen genetic loci for bipolar disorder and schizophrenia," commented first author Evangelos Vassos. "About half of these are shared between these two disorders, indicating they share some, but not all, genetic causes."

Due to the conflicting results, it is clear that more work is needed to determine the role this locus plays in psychosis, but the evidence seems solid that it is associated with bipolar disorder.

PBRM1, the gene implicated in this study, codes for a protein that is involved in chromatin remodeling or "epigenetics," meaning that it influences the ability of a variety of environmental exposures to influence the expression of a range of genes. It has also been previously implicated in the risk for a form of renal cancer.

"There is growing interest in epigenetic mechanisms that might contribute to the development of bipolar disorder. The implication of a gene involved in chromatin remodeling in bipolar disorder risk adds fuel to this fire," commented Dr. John Krystal, Editor of Biological Psychiatry.

Vassos concluded that "future studies may be able to use this information to develop new treatments for these disorders."

Scientists from the Florida campus of The Scripps Research Institute (TSRI) have identified small variations in a number of genes that are closely linked to an increased risk of bipolar disorder, a mental illness that affects nearly six million Americans, according to the National Institute of Mental Health.

"Using samples from some 3,400 individuals, we identified several new variants in genes closely associated with bipolar disorder," said Scripps Florida Professor Ron Davis, who led the new study, which was published recently by the journal Translational Psychiatry.

A strong tendency towards bipolar disorder runs in families; children with a parent or sibling who has bipolar disorder are four to six times more likely to develop the illness, according to the National Institute of Mental Health.

While the genetic basis for bipolar disorder is complex and involves multiple genes, it appears to be associated with a biochemical pathway known as cyclic adenosine monophosphate (cAMP) signaling system. The Davis laboratory and others have previously shown that the cAMP signaling plays a critical role in learning and memory processes. The new study focused on this signaling pathway.

"As far as I know, this has not been done before — to query a single signaling pathway," said Davis. "This is a new approach. The idea is if there are variants in one gene in the pathway that are associated with bipolar disorder, it makes sense there would be variants in other genes of the same signaling pathway also associated with the disorder."

The new study examined variations in 29 genes found in the two common types of bipolar disorder — bipolar disorder I (the most common form and the most severe) and bipolar disorder II. Genes from a total of 1,172 individuals with bipolar disorder I; 516 individuals with bipolar disorder II; and 1,728 controls were analyzed.

Several statistically significant associations were noted between bipolar disorder I and variants in the PDE10A gene. Associations were also found between bipolar disorder II and variants in the DISC1 and GNAS genes.

Davis noted that the location of PDE10A gene expression in the striatum, the part of the brain associated with learning and memory, decision making and motivation, makes it especially interesting as a therapeutic target.

 Lithium is a 'gold standard' drug for treating bipolar disorder, however not everyone responds in the same way. New research published in BioMed Central's open access journal Biology of Mood & Anxiety Disorders finds that this is true at the levels of gene activation, especially in the activation or repression of genes which alter the level the apoptosis (programmed cell death). Most notably BCL2, known to be important for the therapeutic effects of lithium, did not increase in non-responders. This can be tested in the blood of patients within four weeks of treatment.

A research team from Yale University School of Medicine measured the changing levels of gene activity in the blood of twenty depressed adult subjects with bipolar disorder before treatment, and then fortnightly once treatment with lithium carbonate had begun.

Over the eight weeks of treatment there were definite differences in the levels of gene expression between those who responded to lithium (measured using the Hamilton Depression Rating Scale) and those who failed to respond. Dr Robert Beech who led this study explained, "We found 127 genes that had different patterns of activity (turned up or down) and the most affected cellular signalling pathway was that controlled programmed cell death (apoptosis)."

For people who responded to lithium the genes which protect against apoptosis, including Bcl2 and IRS2, were up regulated, while those which promote apoptosis were down regulated, including BAD and BAK1.

The protein coded by BAK1 can open an anion channel in mitochondrial walls which leads to leakage of mitochondrial contents and activation of cell death pathways. Damage similar to this has been seen within the prefrontal cortex of the brain of patients with bipolar disorder. BAD protein is thought to promote BAK1 activity, while Bcl2 binds to BAK1 and prevents its ability to bind to the channel.

Dr Beech continued, "This positive swing in regulation of apoptosis for lithium responders was measurable as early as four weeks after the start of treatment, while in non-responders there was a measureable shift in the opposite direction. It seems then, that increased expression of BCL2 and related genes is necessary for the therapeutic effects of lithium. Understanding these differences in genes expression may lead towards personalized treatment for bipolar disorder in the future."

Flying high, or down in the dumps — individuals suffering from bipolar dis­order alternate between depressive and manic episodes. Re­searchers from the University of Bonn and the Central Institute of Mental Health in Mannheim have now discovered, based on patient data and animal models, how the NCAN gene results in the manic symptoms of bipolar disorder.

The results have been published in the current issue of The American Journal of Psychiatry.

Individuals with bipolar disorder are on an emotional roller coaster. During depressive phases, they suffer from depression, diminished drive and often, also from suicidal thoughts. The manic episodes, however, are characterized by restlessness, euphoria, and delusions of grandeur. The genesis of this disease probably has both hereditary components as well as psychosocial environmental factors.

The NCAN gene plays a major part in how manias manifest

"It has been known that the NCAN gene plays an essential part in bipolar disorder," reports Prof. Dr. Markus M. Nöthen, Director of the Institute of Human Genetics at the University of Bonn. "But until now, the functional connection has not been clear." In a large-scale study, researchers led by the University of Bonn and the Central Institute of Mental Health in Mannheim have now shown how the NCAN gene contributes to the genesis of mania. To do so, they evaluated the genetic data and the related descriptions of symptoms from 1218 patients with differing ratios between the manic and depressive components of bipolar disorder.

Comprehensive data from patients and animal models

Using the patients' detailed clinical data, the researchers tested statis­tically which of the symptoms are especially closely related to the NCAN gene. "Here it became obvious that the NCAN gene is very closely and quite specifically correlated with the manic symptoms," says Prof. Dr. Marcella Rietschel from the Central Institute of Mental Health in Mann­heim. According to the data the gene is, however, not responsible for the depressive episodes in bipolar disorder.

Manic mice drank from sugar solution with abandon

A team working with Prof. Dr. Andreas Zimmer, Director of the Institute of Molecular Psychiatry at the University of Bonn, examined the mole­cular causes effected by the NCAN gene. The researchers studied mice in which the gene had been "knocked out." "It was shown that these animals had no depressive component in their behaviors, only manic ones," says Prof. Zimmer. These knockout mice were, e.g., considerably more active than the control group and showed a higher level of risk-taking behavior. In addition, they tended to exhibit increased reward-seeking behavior, which manifested itself by their unrestrained drinking from a sugar solution offered by the researchers.

Lithium therapy also effective against hyperactivity in mice

Finally, the researchers gave the manic knockout mice lithium — a stan­dard therapy for humans. "The lithium dosage completely stopped the animals' hyperactive behavior," reports Prof. Zimmer. So the results also matched for lithium; the responses of humans and mice regarding the NCAN gene were practically identical. It has been known from prior studies that knocking out the NCAN gene results in a developmental disorder in the brain due to the fact that the production of the neurocan protein is stopped. "As a consequence of this molecular defect, the individuals affected apparently develop manic symptoms later," says Prof. Zimmer.

Opportunity for new therapies

Now the scientists want to perform further studies of the molecular connections of this disorder — also with a view towards new therapies. "We were quite surprised to see how closely the findings for mice and the patients correlated," says Prof. Nöthen. "This level of significance is very rare." With a view towards mania, the agreement between the findings opens up the opportunity to do further molecular studies on the mouse model, whose results will very likely also be applicable to humans. "This is a great prerequisite for advancing the development of new drugs for mania therapy," believes Prof. Rietschel.

The more that we understand the brain, the more complex it becomes. The same can be said about the genetics and neurobiology of psychiatric disorders. For "Mendelian" disorders, like Huntington disease, mutation of a single gene predictably produces a single clinical disorder, following relatively simple genetic principals. Compared to Mendelian disorders, understanding bipolar disorder has been extremely challenging. Its biology is not well understood and its genetics are complex.

In a new paper, Dr. Inti Pedroso and colleagues utilize an integrative approach to probe the biology of bipolar disorder. They combined the results of three genome-wide association studies, which examined the association of common gene variants with bipolar disorder throughout the genome, and a study of gene expression patterns in post-mortem brain tissue from people who had been diagnosed with bipolar disorder. The findings were analyzed within the context of how brain proteins relate to each other based on the Human Protein Reference Database protein-protein interaction network.

"None of our research approaches provides us with sufficient information, by itself, to understand the neurobiology of psychiatric disorders. This innovative paper wrestles with this challenge in a creative way that helps us to move forward in thinking about the neurobiology of bipolar disorder," commented Dr. John Krystal, Editor of Biological Psychiatry.

Dr. Pedroso explained, "We combined information about genetic variation from thousands of cases and controls with brain gene expression data and information from protein databases to identify networks of genes and proteins in the brain that are key in the development of bipolar disorder."

The analysis resulted in the ability to define risk gene variants that were deemed functional, by virtue of the association with changes in gene expression levels, and to group these functional gene variants in biologically meaningful pathways.

The results implicated genes involved in several neural signaling pathways, including the Notch and Wnt signaling pathways. These pathways are key processes in neurotransmission and brain development and these findings indicate they are also likely to be involved in causing this severe disorder. The authors noted that three features stand out among these genes: i) they localized to the human postsynaptic density, which is crucial for neuronal function; ii) their mouse knockouts present altered behavioral phenotypes; and iii) some are known targets of the pharmacological treatments for bipolar disorder.

Dr. Gerome Breen, senior author on the study and Senior Lecturer at King's College London Institute of Psychiatry, said, "Our study provides some of the first evidence to show the biochemical and developmental processes involved in causing risk for developing this life-long and costly illness. We have highlighted potential new avenues for new drug treatments and intervention."

Bipolar disorder is a serious and debilitating condition where individuals experience severe swings in mood between mania and depression. The episodes of low or elevated mood can last days or months, and the risk of suicide is high.

Antidepressants are commonly prescribed to treat or prevent the depressive episodes, but they are not universally effective. Many patients still continue to experience periods of depression even while being treated, and many patients must try several different types of antidepressants before finding one that works for them. In addition, it may take several weeks of treatment before a patient begins to feel relief from the drug's effects.

For these reasons, better treatments for depression are desperately needed. A new study in Biological Psychiatry this week confirms that scientists may have found one in a drug called ketamine.

A group of researchers at the National Institute of Mental Health, led by Dr. Carlos Zarate, previously found that a single dose of ketamine produced rapid antidepressant effects in depressed patients with bipolar disorder. They have now replicated that finding in an independent group of depressed patients, also with bipolar disorder. Replication is an important component of the scientific method, as it helps ensure that the initial finding wasn't accidental and can be repeated.

In this new study, they administered a single dose of ketamine and a single dose of placebo to a group of patients on two different days, two weeks apart. The patients were then carefully monitored and repeatedly completed ratings to 'score' their depressive symptoms and suicidal thoughts.

When the patients received ketamine, their depression symptoms significantly improved within 40 minutes, and remained improved over 3 days. Overall, 79% of the patients improved with ketamine, but 0% reported improvement when they received placebo.

Importantly, and for the first time in a group of patients with bipolar depression, they also found that ketamine significantly reduced suicidal thoughts. These antisuicidal effects also occurred within one hour. Considering that bipolar disorder is one of the most lethal of all psychiatric disorders, these study findings could have a major impact on public health.

"Our finding that a single infusion of ketamine produces rapid antidepressant and antisuicidal effects within one hour and that is fairly sustained is truly exciting," Dr. Zarate commented. "We think that these findings are of true importance given that we only have a few treatments approved for acute bipolar depression, and none of them have this rapid onset of action; they usually take weeks or longer to have comparable antidepressant effects as ketamine does."

Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist, which means that it works by blocking the actions of NMDA. Dr. Zarate added, "Importantly, confirmation that blocking the NMDA receptor complex is involved in generating rapid antidepressant and antisuicidal effects offers an avenue for developing the next generation of treatments for depression that are radically different than existing ones."

 Although the two disorders may seem dissimilar, epilepsy and psychosis are associated. Individuals with epilepsy are more likely to have schizophrenia, and a family history of epilepsy is a risk factor for psychosis. It is not known whether the converse is true, i.e., whether a family history of psychosis is a risk factor for epilepsy.

Multiple studies using varied investigative techniques have shown that patients with schizophrenia and patients with epilepsy show some similar structural brain and genetic abnormalities, suggesting they may share a common etiology.

To investigate this possibility, researchers conducted a population-based study of parents and their children born in Helsinki, Finland. Using data available in two Finnish national registers, the study included 9,653 families and 23,404 offspring.

Individuals with epilepsy had a 5.5-fold increase in the risk of having a psychotic disorder, a 6.3-fold increase in the risk of having bipolar disorder, and an 8.5-fold increase in the risk of having schizophrenia.

They also found that the association between epilepsy and psychosis clusters within families. Individuals with a parental history of epilepsy had a 2-fold increase in the risk of developing psychosis, compared to individuals without a parental history of epilepsy. Individuals with a parental history of psychosis had a 2.7-fold increase in the risk of having a diagnosis of epilepsy, compared to individuals without a parental history of psychosis.

There have been multiple theories regarding the link between epilepsy and psychosis, but most have been predicated on the idea that epilepsy has toxic effects on the brain. However, combined with prior genetic and neurodevelopmental evidence, these new findings suggest a much more complex association, which likely includes a shared genetic vulnerability.

"Our evidence that epilepsy and psychotic illness may cluster within some families indicates that these disorders may be more closely linked than previously thought. We hope that this epidemiological evidence may contribute to the on-going efforts to disentangle the complex pathways that lead to these serious illnesses," said Dr. Mary Clarke, first author of the study and lecturer at Royal College of Surgeons in Ireland.

Dr. John Krystal, Editor of Biological Psychiatry, commented: "We have long known that particular types of epilepsy were associated with psychosis. However, the finding that a parental history of psychosis is associated with an increased risk of epilepsy in the offspring strengthens the mechanistic link between the two conditions."

Over the past 30 years, numerous studies have linked Borna disease virus (BDV) with mental illnesses such as bipolar disorder, schizophrenia, anxiety disorder, and dementia. Genetic fragments and antibodies to this RNA virus, which causes behavior disorders in a range of mammals and birds, have been found to be prevalent in psychiatric patients, but study results have been inconsistent. Now, the first blinded, case-control study to examine this issue finds no association between the virus and psychiatric illness.

The study, conducted by researchers at the Center for Infection and Immunity at Columbia University's Mailman School of Public Health and collaborators at seven other institutions in the U.S., Germany and Australia, can be found online at Molecular Psychiatry.

The scientists evaluated 198 patients in California with schizophrenia, bipolar disorder, and major depressive disorder, carefully matched each one of them with a healthy control of the same sex, age, region, and socio-economic status, and tested blood of patients and controls for the presence of BDV genetic material and antibodies to BDV.

The investigators hypothesized that if the virus was, in fact, associated with a psychiatric disorder, genetic evidence of infection would be apparent in blood samples taken at the onset and/or at the peak of a psychiatric episode, and antibody evidence would be detectable several weeks afterward. Blood samples were therefore collected within six weeks of the onset of an acute episode or clinically significant worsening of symptoms and six weeks later to allow for changes in viral load or antibody levels. Not only did the researchers find no relationship between mental illness and bornavirus, they found no evidence of active or historical infection with BDV in any of the subjects.

"Our study provides compelling evidence that bornaviruses do not play a role in schizophrenia or mood disorders," says Mady Hornig, MD, director of translational research at the Center for Infection and Immunity.

In a commentary in the same issue of the journal, Michael B.A. Oldstone, MD, an expert in molecular virology and central nervous system infections at the Scripps Research Institute, observes that the design and experimental procedures carried out in the Hornig study provide a gold standard for investigating links between persistent viral infection and human disease.

CII director, W. Ian Lipkin, MD, senior author of the paper, notes that "it was concern over the potential role of BDV in mental illness and the inability to identify it using classical techniques that led us to develop molecular methods for pathogen discovery. Ultimately these new techniques enabled us to refute a role for BDV in human disease. But the fact remains that we gained strategies for the discovery of hundreds of other pathogens that have important implications for medicine, agriculture, and environmental health."