Posts tagged huntingtin
Articles and news from the latest research reports.
'Disease in a dish' approach could aid Huntington's disease discovery efforts
Creating induced pluripotent stem cells or iPS cells allows researchers to establish “disease in a dish” models of conditions ranging from Alzheimer’s disease to diabetes. Scientists at Yerkes National Primate Research Center, Emory University have now applied the technology to a model of Huntington’s disease (HD) in transgenic nonhuman primates, allowing them to conveniently assess the efficacy of potential therapies on neuronal cells in the laboratory.
(Image caption: Neural progenitor cells derived from transgenic rhesus macaque iPS cells show features of Huntington’s disease pathology, making them a useful tool for therapeutic discovery.)
The results were published this week in Stem Cell Reports.
"A highlight of our model is that our progenitor cells and neurons developed cellular features of HD such as intranuclear inclusions of mutant Huntingtin protein, which most of the currently available cell models do not present," says senior author Anthony Chan, PhD, DVM, associate professor of human genetics at Emory University School of Medicine and Yerkes National Primate Research Center. "We could use these features as a readout for therapy using drugs or a genetic manipulation."
Chan and his colleagues were the first in the world to establish a transgenic nonhuman primate model of HD. HD is an inherited neurodegenerative disorder that leads to the appearance of uncontrolled movements and cognitive impairments, usually in adulthood. It is caused by a mutation that introduces an expanded region where one amino acid (glutamine) is repeated dozens of times in the huntingtin protein.
The non-human primate model has extra copies of the huntingtin gene that contains the expanded glutamine repeats. In the non-human primate model, motor and cognitive deficits appear more quickly than in most cases of Huntington’s disease in humans, becoming noticeable within the first two years of the monkeys’ development.
First author Richard Carter, PhD, a graduate of Emory’s Genetics and Molecular Biology doctoral program, and his colleagues created iPS cells from the transgenic monkeys by reprogramming cells derived from the skin or dental pulp. This technique uses retroviruses to introduce reprogramming factors into somatic cells and induces a fraction of them to become pluripotent stem cells. Pluripotent stem cells are able to differentiate into any type of cell in the body, under the right conditions.
Carter and colleagues induced the iPS cells to become neural progenitor cells and then differentiated neurons. The iPS-derived neural cells developed intracellular and intranuclear aggregates of the mutant huntingtin protein, a classic sign of Huntington’s pathology, as well as an increased sensitivity to oxidative stress.
The sensitivity to oxidative stress was a useful indicator; it could be ameliorated in cell culture, either by a RNA-based gene knockdown approach, or the drug memantine, which is currently being investigated for Huntington’s disease in a human clinical trial.
"We tested two known experimental interventions, but our findings are a proof of principle that this system could be a valuable tool for the discovery and evaluation of other therapies," Chan says.
(Source: news.emory.edu)
A Gene Linked to Disease Found to Play a Critical Role in Normal Memory Development
It has been more than 20 years since scientists discovered that mutations in the gene huntingtin cause the devastating progressive neurological condition Huntington’s disease, which involves involuntary movements, emotional disturbance and cognitive impairment. Surprisingly little, however, has been known about the gene’s role in normal brain activity.
Now, a study from The Scripps Research Institute’s (TSRI’s) Florida campus and Columbia University shows it plays a critical role in long-term memory.
“We found that huntingtin expression levels are necessary for what is known as long-term synaptic plasticity—the ability of the synapses to grow and change—which is critical to the formation of long-term memory,” said TSRI Assistant Professor Sathyanarayanan V. Puthanveettil, who led the study with Nobel laureate Eric Kandel of Columbia University.
In the study, published recently by the journal PLOS ONE, the team identified an equivalent of the human huntingtin protein in the marine snail Aplysia, a widely used animal model in genetic studies, and found that, just like its human counterpart, the protein in Aplysia is widely expressed in neurons throughout the central nervous system.
Using cellular models, the scientists studied what is known as the sensory-to-motor neuron synapse of Aplysia—in this case, gill withdrawal, a defensive move that occurs when the animal is disturbed.
The study found that the expression of messenger RNAs of huntingtin—messenger RNAs are used to produce proteins from instructions coded in genes—is increased by serotonin, a neurotransmitter released during learning in Aplysia. After knocking down production of the huntingtin protein, neurons failed to function normally.
“During the learning, production of the huntingtin mRNAs is increased both in pre- and post-synaptic neurons—that is a new finding,” Puthanveettil said. “And if you block production of the protein either in pre- or post-synaptic neuron, you block formation of memory.”
The findings could have implications for the development of future treatments of Huntington’s disease. While the full biological functions of the huntingtin protein are not yet fully understood, the results caution against a therapeutic approach that attempts to eliminate the protein entirely.
Huntington’s Disease Protein Helps Wire the Young Brain
The protein that is mutated in Huntington’s disease is critical for wiring the brain in early life, according to a new Duke University study.
(Image caption: The protein associated with Huntington’s disease, Htt, is critical in early brain development. Brains of 5-week-old mice whose Htt was deleted show signs of cellular stress — reactive astrocytes (green) and microglia (white and red) and faulty connections — in brain circuits that have already been linked to the disease. Credit: Spencer McKinstry)
Huntington’s disease is a progressive neurodegenerative disorder that causes a wide variety of symptoms, such as uncontrolled movements, inability to focus or remember, depression and aggression. By the time these symptoms appear, usually in middle age, the disease has already ravaged the brain.
The new findings, published July 9 in the Journal of Neuroscience, add to growing evidence that Huntington’s and other neurodegenerative disorders, such as Alzheimer’s disease, may take root during development, said lead author Cagla Eroglu, an assistant professor of cell biology in the Duke University Medical School, and member of the Duke Institute for Brain Sciences.
“The study is exciting because it means that, if we understand what these developmental errors are, we may be able to interfere with the first stage of the disease, before it shows itself,” Eroglu said.
Several years ago, Eroglu and her team were looking for molecular players involved in the formation of new connections, or synapses, in early brain development in mice when their studies unexpectedly hit on the huntingtin (Htt) protein, which is present throughout the body and which forms clumps in the brain cells of people with Huntington’s disease.
“(Htt) had been implicated in certain cellular functions and synaptic dysfunction in Huntington’s, but the possibility that Htt is playing a direct role in synapse formation was not explored,” Eroglu said.
To understand the protein’s role as synapses form, the scientists created mice in which Htt is deleted only in the cortex, a part of the brain that is implicated in the disease and that controls perception, memory and thought.
At three weeks of age (roughly similar to the first two years of human life), a time when a mouse begins to take in its surroundings through its eyes and ears, the synapses of the mutant mice formed more rapidly compared with those of healthy mice, the scientists found.
But by five weeks, when some synapses typically strengthen while others weaken in a normal process called pruning, the synapses had completely deteriorated in the mutant mice. In collaboration with another Duke researcher, Henry Yin, an assistant professor in psychology & neuroscience, the team also investigated the changes in synaptic function in these mutant mice and found severe alterations of the synaptic physiology.
Not only did the researchers see faulty circuits in the mice missing cortical Htt, they also saw signs of cellular stress in the brain, in the exact spot within the cortex that projects to the striatum, another brain area targeted by Huntington’s disease in people. “There’s something about that particular circuit that is vulnerable to changes in Htt,” Eroglu said.
The researchers also examined what happens in early brain development in a mouse model of Huntington’s disease. Similar to people with the disease, these animals have one normal copy of the Htt gene, and one mutated copy, which produces a protein that is present in cells but in expanded form.
The researchers found the same pattern: the Huntington’s disease model animals have synapses that initially mature much faster than normal in the cortex and then die off.
The new results also suggest that missing Htt for a prolonged period may not only affect the development but also the maintenance of healthy synapses, Eroglu said.
That’s especially relevant to a current strategy for treating Huntington’s disease: dialing down Htt levels in the brain using gene therapy or small-molecule inhibitors. But it has been a challenge to target the mutated copy of the gene, not the normal copy. Interested in the implications of lowering overall Htt levels, the group plans to delete Htt in the mouse brain later in life and measure the number of its synapses.
Other mouse models of the disease are also likely to have these faulty circuits. “We think this is probably a common thing, but that’s something we’re working on: whether we can detect early signs of faulty connections, correct it before the disease starts, and make these mice better,” Eroglu said.
(Source: today.duke.edu)
Fatal cell malfunction ID’d in Huntington’s disease
Researchers believe they have learned how mutations in the gene that causes Huntington’s disease kill brain cells, a finding that could open new opportunities for treating the fatal disorder. Scientists first linked the gene to the inherited disease more than 20 years ago.
Huntington’s disease affects five to seven people out of every 100,000. Symptoms, which typically begin in middle age, include involuntary jerking movements, disrupted coordination and cognitive problems such as dementia. Drugs cannot slow or stop the progressive decline caused by the disorder, which leaves patients unable to walk, talk or eat.
Lead author Hiroko Yano, PhD, of Washington University School of Medicine in St. Louis, found in mice and in mouse brain cell cultures that the disease impairs the transfer of proteins to energy-making factories inside brain cells. The factories, known as mitochondria, need these proteins to maintain their function. When disruption of the supply line disables the mitochondria, brain cells die.
“We showed the problem could be fixed by making cells overproduce the proteins that make this transfer possible,” said Yano, assistant professor of neurological surgery, neurology and genetics. “We don’t know if this will work in humans, but it’s exciting to have a solid new lead on how this condition kills brain cells.”
The findings are available online in Nature Neuroscience.
Huntington’s disease is caused by a defect in the huntingtin gene, which makes the huntingtin protein. Life expectancy after initial onset is about 20 years.
Scientists have known for some time that the mutated form of the huntingtin protein impairs mitochondria and that this disruption kills brain cells. But they have had difficulty understanding specifically how the gene harms the mitochondria.
For the new study, Yano and collaborators at the University of Pittsburgh worked with mice that were genetically modified to simulate the early stages of the disorder.
Yano and her colleagues found that the mutated huntingtin protein binds to a group of proteins called TIM23. This protein complex normally helps transfer essential proteins and other supplies to the mitochondria. The researchers discovered that the mutated huntingtin protein impairs that process.
The problem seems to be specific to brain cells early in the disease. At the same point in the disease process, the scientists found no evidence of impairment in liver cells, which also produce the mutated huntingtin protein.
The researchers speculated that brain cells might be particularly reliant on their mitochondria to power the production and recycling of the chemical signals they use to transmit information. This reliance could make the cells vulnerable to disruption of the mitochondria.
Other neurodegenerative conditions, including Alzheimer’s disease and amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease, have been linked to problems with mitochondria. Scientists may be able to build upon these new findings to better understand these disorders.
(Source: news.wustl.edu)
How Huntington’s Disease Protein Could Cause Death of Neurons
Scientists at the University of Pittsburgh School of Medicine have identified for the first time a key molecular mechanism by which the abnormal protein found in Huntington’s disease can cause brain cell death. The results of these studies, published today in Nature Neuroscience, could one day lead to ways to prevent the progressive neurological deterioration that characterizes the condition.
Huntington’s disease patients inherit from a parent a gene that contains too many repeats of a certain DNA sequence, which results in the production of an abnormal form of a protein called huntingtin (HTT), explained senior investigator Robert Friedlander, M.D., UPMC Professor of Neurosurgery and Neurobiology and chair, Department of Neurological Surgery, Pitt School of Medicine. But until now, studies have not suggested how HTT could cause disease.
“This study connects the dots for the first time and shows how huntingtin can cause problems for the mitochondria that lead to the death of neurons,” Dr. Friedlander said. “If we can disrupt the pathway, we may be able to identify new treatments for this devastating disease.”
Examination of brain tissue samples from both mice and human patients affected by Huntington’s disease showed that mutant HTT collects in the mitochondria, which are the energy suppliers of the cell. Using several biochemical approaches in follow-up mouse studies, the research team identified the mitochondrial proteins that bind to mutant HTT, noting its particular affinity for TIM23, a protein complex that transports other proteins from the rest of the cell into the mitochondria.
Further investigation revealed that mutant HTT inhibited TIM23’s ability to transport proteins across the mitochondrial membrane, slowing metabolic activity and ultimately triggering cell-suicide pathways. The team also found that mutant HTT-induced mitochondrial dysfunction occurred more often near the synapses, or junctions, of neurons, likely impairing the neuron’s ability to communicate or signal its neighbors.
To verify the findings, the researchers showed that producing more TIM23 could overcome the protein transport deficiency and prevent cell death.
“We learned also that these events occur very early in the disease process, not as the result of some other mutant HTT-induced changes,” Dr. Friedlander said. “This means that if we can find ways to intervene at this point, we may be able to prevent neurological damage.”
The team’s next steps include identifying exact binding sites and agents that can influence the interactions of HTT and TIM23.
(Source: upmc.com)
The gene mutation that causes Huntington’s disease appears in every cell in the body, yet kills only two types of brain cells. Why? UCLA scientists used a unique approach to switch the gene off in individual brain regions and zero in on those that play a role in causing the disease in mice.
Published in the April 28 online edition of Nature Medicine, the research sheds light on where Huntington’s starts in the brain. It also suggests new targets and routes for therapeutic drugs to slow the devastating disease, which strikes an estimated 35,000 Americans.
“From day one of conception, the mutant gene that causes Huntington’s appears everywhere in the body, including every cell in the brain,” explained X. William Yang, professor of psychiatry and biobehavioral sciences at the Semel Institute for Neuroscience and Human Behavior at UCLA. “Before we can develop effective strategies to treat the disorder, we need to first identify where it starts and how it ravages the brain.”
Huntington’s disease is passed from parent to child through a mutation in a gene called huntingtin. Scientists blame a genetic “stutter” — a repetitive stretch of DNA at one end of the altered gene—for the cell death and brain atrophy that progressively deprives patients of their ability to move, speak, eat and think clearly. No cure exists, and people with aggressive cases may die in as little as 10 years.
Huntington’s disease targets cells in two brain regions for destruction: the cortex and the striatum. Far more neurons die in the striatum—a cerebral region named after its striped layers of gray and white matter. But it’s unclear whether cortical neurons play a role in the disease, including striatal neurons’ malfunction and death.
Yang’s team used a unique approach to uncover where the mutant gene wreaks the most damage in the brain.
In 2008, Yang collaborated with co-first author Michelle Gray, a former UCLA postdoctoral researcher now at the University of Alabama, to engineer a mouse model for Huntington’s disease. The scientists inserted the entire human huntintin gene, including the stutter, into the mouse genome. As the animals’ brains atrophied, the mice developed motor and psychiatric-like problems similar to the human patients.
In the current study, Yang and Nan Wang, co-first author and UCLA postdoctoral researcher, took the model one step further. They integrated a “genetic scissors” that snipped off the stutter and shut down the defective gene—first in the cortical neurons, then the striatal neurons and finally in both sets of cells. In each case, they measured how the mutant gene influenced disease development in the cells and affected the animals’ brain atrophy, motor and psychiatric-like symptoms.
“The genetic scissors gave us the power to study the role of any cell type in Huntington’s,” said Wang. “We were surprised to learn that cortical neurons play a key role in initiating aspects of the disease in the brain.”
The UCLA team discovered that reducing huntingtin in the cortex partially improved the animals’ symptoms. More importantly, shutting down mutant huntingtin in both the cortical and striatal neurons—while leaving it untouched in the rest of the brain— corrected every symptom they measured in the mice, including motor and psychiatric-like behavioral impairment and brain atrophy.
“We have evidence that the gene mutation highjacks communication between the cortical and striatal neurons,” explained Yang. “Reducing the defective gene in the cortex normalized this communication and helped lessen the disease’s impact on the striatum.”
“Our research helps to shed lights on an age-old question in the field,” he added. “Where does Huntington’s disease start? Equally important, our findings provide crucial insights on where to target therapies to reduce mutant gene levels in the brain—we should target both cortical and striatal neurons.”
Some of the current experimental therapies can be delivered only to limited brain areas, because their properties do not allow them to broadly spread in the brain.
The UCLA team’s next step will be to study how mutant huntingtin affects cortical and striatal neurons’ function and communication, and to identify therapeutic targets that may normalize cellular miscommunication to help slow progression of the disease.
Unlocking a Mystery of Human Disease … in Space
Huntington’s disease is a grim diagnosis. A hereditary disorder with debilitating physical and cognitive symptoms, the disease usually robs adult patients of their ability to walk, balance, and speak. More than 15 years ago, researchers revealed the disorder’s likely cause—an abnormal version of the protein huntingtin; however, the mutant protein’s mechanism is poorly understood, and the disease remains untreatable.
Now, a new project led by Pamela Bjorkman, Max Delbrück Professor of Biology, will investigate whether the huntingtin protein can form crystals in microgravity aboard the International Space Station (ISS)—crystals that are crucial for understanding the molecular structure of the protein. The experiment was launched from Cape Canaveral in Florida on Friday, April 18 aboard the SpaceX CRS-3 cargo resupply mission to the ISS. On Sunday, April 20 the station’s robotic arm captured the mission’s payload, which included the proteins for Bjorkman’s experiment—which is the first Caltech experiment to take place aboard the ISS.
In the experiment, the researchers hope to grow a crystal of the huntingtin protein—the crystal would be an organized, latticelike arrangement of the protein’s molecules—which is needed to determine the molecular structure of the protein. However, molecules of the huntingtin protein tend to aggregate, or clump together, in Earth’s gravity. And this disordered arrangement makes it incredibly hard to parse the protein’s structure, says Gwen Owens, a graduate student in Bjorkman’s lab and a researcher who helped design the study.
"We need crystals for X-ray crystallography, the technique we use to study the protein, in which we shoot an X-ray through the protein crystal and analyze the organized pattern of radiation that scatters off of it," Owens says. "That pattern is what we depend on to identify the location of every carbon, nitrogen, and sulfur atom within the protein; if we shoot an X-ray beam at a clumped, aggregate protein—like huntingtin often is—we can’t get any data from it," she says.
Researchers have previously studied small fragments of crystallized huntingtin, but because of its large size and propensity to clumping, no one has ever successfully grown a crystal of the full-length protein large enough to analyze with X-ray crystallography. To understand what the protein does—and how defects in it lead to the symptoms of Huntington’s disease—the researchers need to study the full-length protein.
Looking for a solution to this problem, Owens was inspired by a few previous studies of protein formation on space shuttles and the ISS—studies suggesting that proteins can form crystals more readily in a condition of near-weightlessness called microgravity. “The previous studies looked at much simpler proteins, but we thought we could make a pretty good case that huntingtin would be an excellent candidate to study on the ISS,” Owens says.
They proposed such an experiment to the Center for the Advancement of Science in Space (CASIS), which manages U.S. research on the ISS, and it was accepted, becoming part of the first Advancing Research Knowledge, or ARK1, mission.
Because Owens and Bjorkman cannot travel with their proteins, and staff and resources are limited aboard the ISS, the crystal will be grown with a Handheld High-Density Protein Crystal Growth device—an apparatus that will allow astronauts to initiate growth of normal and mutant huntingtin protein crystals from a solution of protein molecules with just the flip of a switch.
As the crystals grow larger over a period of several months, samples will come back to Earth via the SpaceX CRS-4 return mission. The results of the experiment are scheduled to drop into the ocean just off the coast of Southern California—along with the rest of the return cargo—sometime this fall. At that point, Owens will finally be able to analyze the proteins.
"Our ideal result would be to have large crystals of the normal and mutant huntingtin proteins right away—on the first try," she says. After analyzing crystals of the full-length protein with X-ray crystallography, the researchers could finally determine huntingtin’s structure—information that will be crucial to developing treatments for Huntington’s disease.
Huntington’s disease: Study discovers potassium boost improves walking in mouse model
Tweaking a specific cell type’s ability to absorb potassium in the brain improved walking and prolonged survival in a mouse model of Huntington’s disease, reports a UCLA study published March 30 in the online edition of Nature Neuroscience. The discovery could point to new drug targets for treating the devastating disease, which strikes one in every 20,000 Americans.
Huntington’s disease is passed from parent to child through a mutation in the huntingtin gene. By killing brain cells called neurons, the progressive disorder gradually deprives patients of their ability to walk, speak, swallow, breathe and think clearly. No cure exists, and patients with aggressive cases can die in as little as 10 years.
The laboratories of Baljit Khakh, a professor of physiology and neurobiology, and Michael Sofroniew, a professor of neurobiology, teamed up at the David Geffen School of Medicine at UCLA to unravel the role played in Huntington’s by astrocytes—large, star-shaped cells found in the brain and spinal cord.
Brain Degeneration In Huntington’s Disease Caused By Amino Acid Deficiency
Working with genetically engineered mice, Johns Hopkins neuroscientists report they have identified what they believe is the cause of the vast disintegration of a part of the brain called the corpus striatum in rodents and people with Huntington’s disease: loss of the ability to make the amino acid cysteine. They also found that disease progression slowed in mice that were fed a diet rich in cysteine, which is found in foods such as wheat germ and whey protein.
Their results suggest further investigation into cysteine supplementation as a candidate therapeutic in people with the disease.
Up to 90 percent of the human corpus striatum, a brain structure that moderates mood, movement and cognition, degenerates in people with Huntington’s disease, a condition marked by widespread motor and intellectual disability. And while the genetic mutation underlying Huntington’s disease has long been known, the precise cause of that degeneration has remained a mystery.
In a report on their discovery in the advanced online publication of Nature on March 26, the Johns Hopkins researchers, led by Solomon Snyder, M.D., tracked the degenerative process to the absence of an enzyme, cystathionine gamma lyase, or CSE.
"Usually it’s very hard, if not impossible, to develop straightforward mechanisms that explain what’s going on in a disease. What’s even harder is even if you can find a mechanism that causes a tissue to rot, usually there’s nothing you can do about it,” says Snyder, a professor of neuroscience at the Johns Hopkins University School of Medicine. “In this case, there is."
Huntington’s disease, an inherited disorder, does its damage because of abnormal DNA coding for the amino acid glutamine. Healthy individuals have some 15 to 20 DNA “repeats” in that part of their genetic code, while Huntington’s disease gene carriers have more than 36 — and often upward of 100. Children born to a parent carrier have a 50/50 chance of inheriting the disorder, and the greater the number of repeats, the earlier the age of onset of the incurable disorder.
Bindu Diana Paul, Ph.D., a molecular neuroscientist and faculty instructor in Snyder’s laboratory, was studying mice lacking CSE, which helps make the amino acid cysteine and hydrogen sulfide that moderate blood pressure and heart function. Paul, who had previous research experience with Huntington’s disease, says she was startled to observe that her mutant mice also behaved a lot like those with the disease.
When a normal mouse is dangled upside down from its tail, it will twist and turn and try to bite the offending hand, she explains. But her CSE-knockout mice stayed relatively still and clasped their paws together — the same behavior she’d observed in mice with the rodent equivalent of Huntington’s disease. “It looked like there was a neurological deficit,” Paul says. “But nobody had looked at CSE in the brain.”
Paul and Snyder began monitoring CSE in mouse and human brain tissues and found considerably less CSE in all diseased tissues. All people carry some normal huntingtin protein made by the Huntington’s disease gene, although the protein’s function remains elusive. But people with Huntington’s disease also carry mutant huntingtin proteins. Snyder and his team saw that the mutant proteins were attaching themselves to a crucial protein responsible for turning the CSE gene on or off, which ultimately led the diseased rodent and human brain tissues to be deprived of cysteine.
To see if loss of cysteine was directly responsible for the symptoms associated with Huntington’s disease, the Johns Hopkins team turned to readily available sources of the substance in everyday foods and fed mice a cysteine-rich diet.
The results, Paul says, were striking. When those mice were dangled from their tails, they resumed struggling, although with a bit less vigor than their healthy peers. They were able to grip an object with greater strength, and they took longer to fall off a balancing apparatus than CSE-knockout mice. Their life expectancies increased one to two weeks.
Snyder and Paul say they are cautiously optimistic about the results, noting that although they suggest a possible treatment for Huntington’s disease, it’s clear that a high cysteine diet merely slows rather than halts the progression of the disease. Moreover, the results in live mice may not occur in humans.
(Source: hopkinsmedicine.org)
Huntington disease prevention trial shows creatine safe, suggests slowing of progression
The first clinical trial of a drug intended to delay the onset of symptoms of Huntington disease (HD) reveals that high-dose treatment with the nutritional supplement creatine was safe and well tolerated by most study participants. In addition, neuroimaging showed a treatment-associated slowing of regional brain atrophy, evidence that creatine might slow the progression of presymptomatic HD. The Massachusetts General Hospital (MGH) study also utilized a novel design that allowed participants – all of whom were at genetic risk for the neurodegenerative disorder – to enroll without having to learn whether or not they carried the mutation that causes HD.
"More than 90 percent of those in the United States who know they are at risk for HD because of their family history have abstained from genetic testing, often because they fear discrimination or don’t want to face the stress and anxiety of knowing they are destined to develop such a devastating disease," says H. Diana Rosas, MD, of the MassGeneral Institute for Neurodegenerative Disease (MGH-MIND), lead and corresponding author of the paper that will appear in the March 11 issue of Neurology and has been released online. “Many of these individuals would still like to help find treatments, and this trial design allows them to participate while respecting their autonomy, their right not to know their personal genetic information.”
Among the ways that the mutated form of the huntingtin protein damages brain cells is by interfering with cellular energy production, leading to a depletion of ATP, the molecule that powers most biological processes. Known to help restore ATP and maintain cellular energy, creatine is being investigated to treat a number of neurological conditions – including Parkinson disease, amyotrophic lateral sclerosis and spinal cord injury. Studies in mouse models of HD showed that creatine raises brain ATP levels and protects against neurodegeneration. Previous clinical trials of creatine in symptomatic HD patients have been limited in scale, involved daily doses of 10 grams or less, and did not provide evidence of potential efficacy. Based on the results of a pilot study at MGH that evaluated doses as high as 40 grams, participants in the current study received doses of up to 30 grams daily.
The phase II PRECREST trial enrolled 64 adult participants - 19 who knew they carried the mutated form of the HD gene and 45 with a 50 percent risk of having inherited the HD mutation. Genetic testing, results of which were made available only to the study statistician and not to study staff or participants, confirmed the genetic status of those who had previously been tested and revealed an additional 26 presymptomatic carriers of the mutated gene, for a total of 47 participants with presymptomatic HD and 17 controls.
For the first 6 months of the trial, participants were randomized into two groups, regardless of gene status. One group received twice-daily oral doses of creatine, up to a maximum of 30 grams per day, the other received placebo. After that first phase, all participants received creatine for an additional 12 months. Participants were assessed at regular study visits for adverse effects, and dosage levels were adjusted, if necessary, to reduce unpleasant side effects. Additional tests – cognitive assessments, measurement of blood markers and MRI brain scans – were conducted at the trial’s outset, at 6 months and at the end of the study period.
During the first phase of the trial more than three-quarters of those randomized to creatine tolerated a daily dose of 15 grams or more, and more than two -thirds tolerated the full 30-gram dose. Throughout the entire trial, a total of 15 participants – including several who knew they carried the HD mutation – discontinued taking creatine because of gastrointestinal discomfort, the taste of the drug, inconvenience, or the stress of being constantly reminded of their HD risk. Other than occasional diarrhea and nausea, few adverse events were associated with creatine.
In participants who carried the HD mutation, the MRI scans taken at the outset of the trial had revealed significant atrophy in regions of the cerebral cortex and basal ganglia known to be affected by the disease. Followup MRI scans at six months showed a slower rate of atrophy in participants taking creatine compared to those on placebo. At the end of the second phase, the rate of brain atrophy had also slowed in presymptomatic participants that started taking creatine after 6 months on placebo.
In addition to suggesting that creatine could slow the progression of HD, these results also imply that neuroimaging may provide a useful biomarker of disease modification in studies of other potential treatments. While participants with the mutation had performed less well than controls on the cognitive tests at the study outset, creatine treatment had no significant effect on those measures, possibly because the tests were not sensitive enough to detect subtle changes that might occur during such a brief time period, the authors note.
"The results of this trial suggest that the prevention or delay of HD symptoms is feasible, that at-risk individuals can participate in clinical trials – even if they do not want to learn their genetic status – and that useful biomarkers can be developed to help assess therapeutic benefits," says senior author Steven Hersch, MD, PhD, of MGH-MIND. "In addition, we believe our study design sets an important precedent for other genetic diseases and will help inform discussions of how clinical research can coexist with deep concerns about genetic privacy and patient autonomy."