Posts tagged mutations
Posts tagged mutations
Scientists have identified a set of tests that could help identify whether and how Huntington’s disease (HD) is progressing in groups of people who are not yet showing symptoms. The latest findings from the TRACK-HD study*, published Online First in The Lancet Neurology, could be used to assess whether potential new treatments are slowing the disease up to 10 years before the development of noticeable symptoms.
“Currently, the effectiveness of a new drug is decided by its ability to treat symptoms. These new tests could be used in future preventative drug trials in individuals who are gene positive for HD but are not yet showing overt motor symptoms. These people have the most to gain by initiating treatment early to delay the start of these overt symptoms and give them a high quality of life for a longer period of time”, explains lead author Sarah Tabrizi from University College London’s Institute of Neurology.
The TRACK-HD investigators have previously reported a range of tests that could be used in clinical trials to assess the effectiveness of potential disease-modifying drugs in people who already show signs of the disease. But in individuals without noticeable symptoms there was little evidence of a decline in function over two years, limiting the ability to test new drugs early in the disease course.
HD is caused by the mutation of a single gene on chromosome 4, which causes a part of the DNA (known as a CAG motif) to repeat many more times than it is supposed to. The length of the CAG repeat is known to be a major determinant of the age at which symptoms of the disease are likely to start, but its contribution to progression is unclear.
Here the TRACK-HD investigators extend the study to a third year with the aim of identifying some of the earliest biological changes in individuals with presymptomatic HD, giving additional power to predict how the disease may progress beyond that already expected from age and CAG length.
Over 3 years, baseline measures derived from brain imaging were the clearest markers of disease progression and future diagnosis, above and beyond the effect of age and CAG count, in gene carriers up to 20 years before they were expected to show symptoms.
In particular, the investigators suggest that measuring volume change in white matter and the caudate and putamen regions might be future endpoints for treatment trials.
In individuals up to 10 years away from developing symptoms, there was also significant deterioration in performance on a number of motor (movement) and cognitive (intellectual function) tasks compared with controls, and the frequency of apathy increased. Finger tapping was the most sensitive of the motor assessments, while the symbol digit modality test proved to be the most sensitive of the cognitive measures.
According to Tabrizi, “A new generation of drugs will be ready for human trials in the very near future. Diagnosis in HD is something of an artificial construct at onset of motor symptoms, and this study now gives us a number of other, more well-defined parameters that correlate with disease progression. Something that suggests we’re moving towards a more biological, as opposed to physical, definition of disease progression that reduces the importance of an ‘onset event’ is great news. By extending the reach of clinical trials to include individuals who are currently free of overt symptoms there is a realistic future possibility that treatments in the pipeline can significantly improve the quality of life for patients and families.”**
Writing in a linked Comment, Francis O. Walker, M.D., from Wake Forest School of Medicine in the USA says that the TRACK-HD investigators have set the standard for observational studies in other neurodegenerative diseases, adding that, “Virtual roadmaps of disease in the minds of practitioners are good for care in the framework of the traditional patient encounter, but it takes substantial effort, teamwork, and genius to turn them into rigorous, quantifiable timelines that can be used to test efficacy in future therapeutic trials.”
* The Track-HD study was established to identify differences between people carrying the HD mutation at different stages and healthy controls that could be used to accurately predict the progression of HD using a variety of techniques to assess changes in brain function, motor function, behaviour, and cognition. 366 individuals from Canada, France, the Netherlands and the UK were enrolled: 120 presymptomatic carriers of the HD gene mutation, 123 patients with early symptomatic HD, and 123 healthy controls.
Researchers at the University Department of Neurology at the MedUni Vienna have identified a gene behind an epilepsy syndrome, which could also play an important role in other idiopathic (genetically caused) epilepsies. With the so-called “next generation sequencing”, with which genetic changes can be identified within a few days, it was ascertained that the CNTN2 gene is defective in this type of epilepsy.
This was investigated by a team led by Elisabeth Stögmann in collaboration with Cairo’s Ain Shams University and the Helmholtz Centre Munich with reference to a particular Egyptian family, in which five sick children have resulted from the marriage of one healthy cousin to his, likewise healthy, second cousin. The children affected suffer from a specific epilepsy syndrome, in which different types of epileptic attacks occur. This constellation has the “advantage”, according to Stögmann, that both alleles of the gene, which is how one designates different forms of the gene, demonstrate this defect: “As a result the defect becomes symptomatic and identifiable.
“20,000 to 25,000 genes, including all the “protein coding” ones, were sequenced for this. When this was done a mutation was found in the CNTN2 gene. CNTN2 undertakes an important function in the anchoring of potassium channels to the synapses. The mutation makes it no longer possible to generate this protein and, as a consequence, the potassium channels no longer remain affixed to the synapses. The researchers suspect that the epilepsy in this family is triggered by the altered function of the potassium channels.
This discovery, which has now been published in the top journal “Brain”, is providing the stimulus for further research to investigate this particular gene in other epilepsy patients as well. Approximately one percent of the population suffers from active epilepsy in which regular epileptic fits occur. The danger of suffering from an epileptic fit once in your life lies at approximately four to five percent. Genetic factors play a major part in the occurrence of epilepsies.
Giant axonal neuropathy (GAN) is a rare genetic disorder that causes central and peripheral nervous system dysfunction. GAN is known to be caused by mutations in the gigaxonin gene and is characterized by tangling and aggregation of neural projections, but the mechanistic link between the genetic mutation and the effects on neurons is unclear. In this issue of the Journal of Clinical Investigation, Robert Goldman and colleagues at Northwestern University uncover how mutations in gigaxonin contribute to neural aggregation.They demonstrated that gigaxonin regulates the degradation of neurofilament proteins, which help to guide outgrowth and morphology of neural projections. Loss of gigaxonin in either GAN patient cells or transgenic mice increased levels of neurofilament proteins, causing tangling and aggregation of neural projections. Importantly, expression of gigaxonin allowed for clearance of neurofilament proteins in neurons. These findings demonstrate that mutations in gigaxonin cause accumulation of neurofilament proteins and shed light on the molecular pathology of GAN.
The St. Jude Children’s Research Hospital – Washington University Pediatric Cancer Genome Project has identified mutations responsible for more than half of a subtype of childhood brain tumor that takes a high toll on patients. Researchers also found evidence the tumors are susceptible to drugs already in development.
The study focused on a family of brain tumors known as low-grade gliomas (LGGs). These slow-growing cancers are found in about 700 children annually in the U.S., making them the most common childhood tumors of the brain and spinal cord. For patients whose tumors cannot be surgically removed, the long-term outlook remains bleak due to complications from the disease and its ongoing treatment. Nationwide, surgery alone cures only about one-third of patients.
Using whole genome sequencing, researchers identified genetic alterations in two genes that occurred almost exclusively in a subtype of LGG termed diffuse LGG. This subtype cannot be cured surgically because the tumor cells invade the healthy brain. Together, the mutations accounted for 53 percent of the diffuse LGG in this study. Researchers also demonstrated that one of the mutations, which had not previously been linked to brain tumors, caused tumors when introduced into the glial brain cells of mice.
The findings appear in the April 14 advance online edition of the scientific journal Nature Genetics.
“This subtype of low-grade glioma can be a nasty chronic disease, yet prior to this study we knew almost nothing about its genetic alterations,” said David Ellison, M.D., Ph.D., chair of the St. Jude Department of Pathology and the study’s corresponding author. The first author is Jinghui Zhang, Ph.D., an associate member of the St. Jude Department of Computational Biology.
The Pediatric Cancer Genome Project is using next-generation whole genome sequencing to determine the complete normal and cancer genomes of children and adolescents with some of the least understood and most difficult to treat cancers. Scientists believe that studying differences in the 3 billion chemical bases that make up the human genome will provide the scientific foundation for the next generation of cancer care.
“We were surprised to find that many of these tumors could be traced to a single genetic alteration,” said co-author Richard K. Wilson, Ph.D., director of The Genome Institute at Washington University School of Medicine in St. Louis. “This is a major pathway through which low-grade gliomas develop and it provides new clues to explore as we search for better treatments.”
The study involved whole genome sequencing of 39 paired tumor and normal tissue samples from 38 children and adolescents with different subtypes of LGG and related tumors called low-grade glioneuronal tumors (LGGNTs). Although many cancers develop following multiple genetic abnormalities, 62 percent of the 39 tumors in this study stemmed from a single genetic alteration.
Previous studies have linked LGGs to abnormal activation of the MAPK/ERK pathway. The pathway is involved in regulating cell division and other processes that are often disrupted in cancer. Until now, however, the genetic alterations involved in driving this pathway were unknown for some types of LGG and LGGNT.
This study linked activation in the pathway to duplication of a key segment of the FGFR1 gene, which investigators discovered in brain tumors for the first time. The segment is called a tyrosine kinase domain. It functions like an on-off switch for several cell signaling pathways, including the MAPK/ERK pathway. Investigators also demonstrated that experimental drugs designed to block activity along two altered pathways worked in cells with theFGFR1 tyrosine kinase domain duplication. “The finding suggests a potential opportunity for using targeted therapies in patients whose tumors cannot be surgically removed,” Ellison said.
Researchers also showed that the FGFR1 abnormality triggered an aggressive brain tumor in glial cells from mice that lacked the tumor suppressor gene Trp53.
Whole-genome sequencing found previously undiscovered rearrangements in the MYB and MYBL1 genes in diffuse LGGs. These newly identified abnormalities were also implicated in switching on the MAPK/ERK pathway.
Researchers checked an additional 100 LGGs and LGGNTs for the same FGFR1, MYB and MYBL1 mutations. Overall, MYB was altered in 25 percent of the diffuse LGGs, and 24 percent had alterations in FGFR1. Researchers also turned up numerous other mutations that occurred in just a few tumors. The affected genes included BRAF, RAF1, H3F3A, ATRX, EP300, WHSC1 and CHD2.
“The Pediatric Cancer Genome Project has provided a remarkable opportunity to look at the genomic landscape of this disease and really put the alterations responsible on the map. We can now account for the genetic errors responsible for more than 90 percent of low-grade gliomas,” Ellison said. “The discovery that FGFR1 and MYB play a central role in childhood diffuse LGG also serves to distinguish the pediatric and adult forms of the disease.”
Mutations found in individuals with autism block the action of molecules made by the brain that act on the same receptors that marijuana’s active chemical acts on, according to new research reported online April 11 in the Cell Press journal Neuron. The findings implicate specific molecules, called endocannabinoids, in the development of some autism cases and point to potential treatment strategies.
“Endocannabinoids are molecules that are critical regulators of normal neuronal activity and are important for many brain functions,” says first author Dr. Csaba Földy, of Stanford University Medical School. “By conducting studies in mice, we found that neuroligin-3, a protein that is mutated in some individuals with autism, is important for relaying endocannabinoid signals that tone down communication between neurons.”
When the researchers introduced different autism-associated mutations in neuroligin-3 into mice, this signaling was blocked and the overall excitability of the brain was changed.
“These findings point out an unexpected link between a protein implicated in autism and a signaling system that previously had not been considered to be particularly important for autism,” says senior author Dr. Thomas Südhof, also of Stanford. “Thus, the findings open up a new area of research and may suggest novel strategies for understanding the underlying causes of complex brain disorders.”
The results also indicate that targeting components of the endocannabinoid signaling system may help reverse autism symptoms.
The study’s findings resulted from a research collaboration between the Stanford laboratories of Dr. Südhof and Dr. Robert Malenka, who is also an author on the paper.
UC Irvine neurobiologists have found a novel molecular mechanism that helps trigger the formation of long-term memory. The researchers believe the discovery of this mechanism adds another piece to the puzzle in the ongoing effort to uncover the mysteries of memory and, potentially, certain intellectual disabilities.
In a study led by Marcelo Wood of UC Irvine’s Center for the Neurobiology of Learning & Memory, the team investigated the role of this mechanism – a gene designated Baf53b – in long-term memory formation. Baf53b is one of several proteins making up a molecular complex called nBAF.
Mutations in the proteins of the nBAF complex have been linked to several intellectual disorders, including Coffin-Siris syndrome, Nicolaides-Baraitser syndrome and sporadic autism. One of the key questions the researchers addressed is how mutations in components of the nBAF complex lead to cognitive impairments.
In their study, Wood and his colleagues used mice bred with mutations in Baf53b. While this genetic modification did not affect the mice’s ability to learn, it did notably inhibit long-term memories from forming and severely impaired synaptic function.
“These findings present a whole new way to look at how long-term memories form,” said Wood, associate professor of neurobiology & behavior. “They also provide a mechanism by which mutations in the proteins of the nBAF complex may underlie the development of intellectual disability disorders characterized by significant cognitive impairments.”
How does this mechanism regulate gene expression required for long-term memory formation? Most genes are tightly packaged by a chromatin structure – chromatin being what compacts DNA so that it fits inside the nucleus of a cell. That compaction mechanism represses gene expression. Baf53b, and the nBAF complex, physically open the chromatin structure so specific genes required for long-term memory formation are turned on. The mutated forms of Baf53b did not allow for this necessary gene expression.
“The results from this study reveal a powerful new mechanism that increases our understanding of how genes are regulated for memory formation,” Wood said. “Our next step is to identify the key genes the nBAF complex regulates. With that information, we can begin to understand what can go wrong in intellectual disability disorders, which paves a path toward possible therapeutics.”
Findings appear online today in Nature Neuroscience.
New research, published in Neuron, gives insight into how single mutations in the VCP gene cause a range of neurological conditions including a form of dementia called Inclusion Body Myopathy, Paget’s Disease of the Bone and Frontotemporal Dementia (IBMPFD), and the motor neuron disease Amyotrophic Lateral Sclerosis (ALS).
Single mutations in one gene rarely cause such different diseases. This study shows that these mutations disrupt energy production in cells shedding new light on the role of VCP in these multiple disorders.
In healthy cells VCP helps remove damaged mitochondria, the energy-producing engines of cells. The mutant protein can’t do this and as a result, the dysfunctional mitochondria build up.
The new study led by Dr Fernando Bartolome, Dr Helene Plun-Favreau and Dr Andrey Abramov of the UCL Institute of Neurology, found that mitochondria are damaged in cells from patients with mutant VCP. Mitochondria generate a cell’s energy, and the study found these damaged mitochondria are less efficient, burning more nutrients but producing less energy. This reduction in available energy makes cells more vulnerable, which could explain why mutations in the VCP gene lead to neurological disorders.
Lead author Dr Fernando Bartolome said, “We have found that VCP mutations are associated with mitochondrial dysfunction. VCP had previously been shown to be important in the removal of damaged mitochondria and proteins, accumulation of which is potentially very toxic to cells. A single mutation in the VCP gene could cause multiple neurological diseases because a different type of protein is accumulating in each disorder”.
In the study, the researchers used live imaging techniques to examine the functioning of mitochondria in patient cells carrying three independent VCP mutations, and in nerve cells in which the amount of VCP has been reduced.
“The next step will be to find small molecules able to correct the mitochondrial dysfunction in the VCP deficient cells”, added Dr Bartolome .
Dr Brian Dickie, the Motor Neuron Disease Association’s Director of Research Development says: “Neurons - and motor neurons in particular - are incredibly energy hungry cells. These new findings from the team at UCL show that there is a significant interruption of energy supply in this hereditary form of MND, which has strong implications for understanding the degenerative process underpinning all forms of the disease.”
A discovery using stem cells from a patient with motor neurone disease could help research into treatments for the condition.
The study used a patient’s skin cells to create motor neurons - nerve cells that control muscle activity - and the cells that support them called astrocytes.
Researchers studied these two types of cells in the laboratory. They found that a protein expressed by abnormalities in a gene linked to motor neurone disease, which is called TDP-43, caused the astrocytes to die.
The study, led by the University of Edinburgh and funded by the Motor Neurone Disease Association, provides fresh insight into the mechanisms involved in the disease.
Although TDP-43 mutations are a rare cause of motor neurone disease (MND), scientists are especially interested in the gene because in the vast majority of MND patients, TDP-43 protein (made by the TDP-43 gene) forms pathological clumps inside motor neurons.
Motor neurones die in MND leading to paralysis and early death.
This study shows for the first time that abnormal TDP-43 protein causes death of astrocytes.
The researchers, however, found that the damaged astrocytes were not directly toxic to motor neurons.
Motor neurone disease is a devastating and ultimately fatal condition, for which there is no cure or effective treatment. -Professor Siddharthan Chandran (Director of the Euan Macdonald Centre for Motor Neurone Disease Research)
Better understanding the role of astrocytes could help to inform research into treatments for motor neurone disease (MND).
These findings, published in the journal Proceedings of the National Academy of Sciences, are significant as they show that different mechanisms are at work in different types of MND.
It is not just a question of looking solely at motor neurons, but also the cells that surround them, to understand why motor neurones die. Our aim is to find ways to slow down progression of this devastating disease and ultimately develop a cure. -Professor Siddharthan Chandran (Director of the Euan Macdonald Centre for Motor Neurone Disease Research)
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.”
Because half of all instances of hearing loss are linked to genetic mutations, advanced gene research is an invaluable tool for uncovering causes of deafness — and one of the biggest hopes for the development of new therapies. Now Prof. Karen Avraham of the Sackler Faculty of Medicine at Tel Aviv University has discovered a significant mutation in a LINC family protein — part of the cells of the inner ear — that could lead to new treatments for hearing disorders.
Her team of researchers, including Dr. Henning Horn and Profs. Colin Stewart and Brian Burke of the Institute of Medical Biology at A*STAR in Singapore, discovered that the mutation causes chaos in a cell’s anatomy. The cell nucleus, which contains our entire DNA, moves to the top of the cell rather than being anchored to the bottom, its normal place. Though this has little impact on the functioning of most of the body’s cells, it’s devastating for the cells responsible for hearing, explains Prof. Avraham. “The position of the nucleus is important for receiving the electrical signals that determine proper hearing,” she explains. “Without the ability to receive these signals correctly, the entire cascade of hearing fails.”
This discovery, recently reported in the Journal of Clinical Investigation, may be a starting point for the development of new therapies. In the meantime, the research could lead towards work on a drug that is able to mimic the mutated protein’s anchoring function, and restore hearing in some cases, she suggests.