Posts tagged genetic variations
Articles and news from the latest research reports.
Schizophrenia not a single disease but multiple genetically distinct disorders
New research shows that schizophrenia isn’t a single disease but a group of eight genetically distinct disorders, each with its own set of symptoms. The finding could be a first step toward improved diagnosis and treatment for the debilitating psychiatric illness.
The research at Washington University School of Medicine in St. Louis is reported online Sept. 15 in The American Journal of Psychiatry.
About 80 percent of the risk for schizophrenia is known to be inherited, but scientists have struggled to identify specific genes for the condition. Now, in a novel approach analyzing genetic influences on more than 4,000 people with schizophrenia, the research team has identified distinct gene clusters that contribute to eight different classes of schizophrenia.
“Genes don’t operate by themselves,” said C. Robert Cloninger, MD, PhD, one of the study’s senior investigators. “They function in concert much like an orchestra, and to understand how they’re working, you have to know not just who the members of the orchestra are but how they interact.”
Cloninger, the Wallace Renard Professor of Psychiatry and Genetics, and his colleagues matched precise DNA variations in people with and without schizophrenia to symptoms in individual patients. In all, the researchers analyzed nearly 700,000 sites within the genome where a single unit of DNA is changed, often referred to as a single nucleotide polymorphism (SNP). They looked at SNPs in 4,200 people with schizophrenia and 3,800 healthy controls, learning how individual genetic variations interacted with each other to produce the illness.
In some patients with hallucinations or delusions, for example, the researchers matched distinct genetic features to patients’ symptoms, demonstrating that specific genetic variations interacted to create a 95 percent certainty of schizophrenia. In another group, they found that disorganized speech and behavior were specifically associated with a set of DNA variations that carried a 100 percent risk of schizophrenia.
“What we’ve done here, after a decade of frustration in the field of psychiatric genetics, is identify the way genes interact with each other, how the ‘orchestra’ is either harmonious and leads to health, or disorganized in ways that lead to distinct classes of schizophrenia,” Cloninger said.
Although individual genes have only weak and inconsistent associations with schizophrenia, groups of interacting gene clusters create an extremely high and consistent risk of illness, on the order of 70 to 100 percent. That makes it almost impossible for people with those genetic variations to avoid the condition. In all, the researchers identified 42 clusters of genetic variations that dramatically increased the risk of schizophrenia.
“In the past, scientists had been looking for associations between individual genes and schizophrenia,” explained Dragan Svrakic, PhD, MD, a co-investigator and a professor of psychiatry at Washington University. “When one study would identify an association, no one else could replicate it. What was missing was the idea that these genes don’t act independently. They work in concert to disrupt the brain’s structure and function, and that results in the illness.”
Svrakic said it was only when the research team was able to organize the genetic variations and the patients’ symptoms into groups that they could see that particular clusters of DNA variations acted together to cause specific types of symptoms.
Then they divided patients according to the type and severity of their symptoms, such as different types of hallucinations or delusions, and other symptoms, such as lack of initiative, problems organizing thoughts or a lack of connection between emotions and thoughts. The results indicated that those symptom profiles describe eight qualitatively distinct disorders based on underlying genetic conditions.
The investigators also replicated their findings in two additional DNA databases of people with schizophrenia, an indicator that identifying the gene variations that are working together is a valid avenue to explore for improving diagnosis and treatment.
By identifying groups of genetic variations and matching them to symptoms in individual patients, it soon may be possible to target treatments to specific pathways that cause problems, according to co-investigator Igor Zwir, PhD, research associate in psychiatry at Washington University and associate professor in the Department of Computer Science and Artificial Intelligence at the University of Granada, Spain.
And Cloninger added it may be possible to use the same approach to better understand how genes work together to cause other common but complex disorders.
“People have been looking at genes to get a better handle on heart disease, hypertension and diabetes, and it’s been a real disappointment,” he said. “Most of the variability in the severity of disease has not been explained, but we were able to find that different sets of genetic variations were leading to distinct clinical syndromes. So I think this really could change the way people approach understanding the causes of complex diseases.”
(Source: news.wustl.edu)
Autism Speaks Through Gene Expression
Autism spectrum disorders affect nearly 1 in 88 children, with symptoms ranging from mild personality traits to severe intellectual disability and seizures. Understanding the altered genetic pathways is critical for diagnosis and treatment. New work to examine which genes are responsible for autism disorders will be presented at the 57th Annual Meeting of the Biophysical Society (BPS), held Feb. 2-6, 2013, in Philadelphia, Pa.
“Autism is the most inheritable of neurodevelopmental disorders,” explains Rajini Rao of Johns Hopkins University in Baltimore, Md., “but identifying the underlying genes is difficult since no single gene contributes more than a tiny fraction of autism cases.” Rather, she continues, “mutations in many different genes variably affect a few common pathways.”
A team of scientists at Johns Hopkins and Tel Aviv University in Israel looked at genetic variations in DNA sequence in the ion transporter NHE9 and found that autism-associated variants in NHE9 result in a profound loss of transporter function. “Altering levels of this transporter at the synapse may modulate critical proteins on the cell surface that bring in nutrients or neurotransmitters such as glutamate,” says Rao. “Elevated glutamate levels are known to trigger seizures, possibly explaining why autistic patients with mutations in these ion transporters also have seizures.”
A unique aspect of the team’s approach was that they exploited decades of basic research done in bacteria and yeast to study a complex human neurological disorder. First, the group at Tel Aviv University, led by Nir Ben-Tal, built structural models of NHE9 using a bacterial relative as a template, allowing the Rao laboratory at Johns Hopkins to use the simple baker’s yeast for screening the mutations. In the future, as genomic information becomes readily available for everyone, such easy, inexpensive, and rapid screening methods will be essential to evaluate rare genetic variants in autism and other disorders.
Rao and her team are optimistic about the potential benefits of their latest findings. “Although the research is still at an early stage, drugs that target the cellular pathways regulated by NHE9 could compensate for its loss of function and lead to potential therapy in the future,” Rao says. “These findings add a new candidate for genetic screening of at-risk patients that may lead to better diagnosis or treatment of autism.”