Posts tagged genetic disorders
Articles and news from the latest research reports.
Biologists Reprogram Skin Cells to Mimic Rare Disease
Johns Hopkins stem cell biologists have found a way to reprogram a patient’s skin cells into cells that mimic and display many biological features of a rare genetic disorder called familial dysautonomia. The process requires growing the skin cells in a bath of proteins and chemical additives while turning on a gene to produce neural crest cells, which give rise to several adult cell types. The researchers say their work substantially expedites the creation of neural crest cells from any patient with a neural crest-related disorder, a tool that lets physicians and scientists study each patient’s disorder at the cellular level.
Previously, the same research team produced customized neural crest cells by first reprogramming patient skin cells into induced pluripotent stem (iPS) cells, which are similar to embryonic stem cells in their ability to become any of a broad array of cell types.
“Now we can circumvent the iPS cells step, saving seven to nine months of time and labor and producing neural crest cells that are more similar to the familial dysautonomia patients’ cells,” says Gabsang Lee, Ph.D., an assistant professor of neurology at the Institute for Cell Engineering and the study’s senior author. A summary of the study was published online in the journal Cell Stem Cell on Aug. 21.
Neural crest cells appear early in human and other animal prenatal development, and they give rise to many important structures, including most of the nervous system (apart from the brain and spinal cord), the bones of the skull and jaws, and pigment-producing skin cells. Dysfunctional neural crest cells cause familial dysautonomia, which is incurable and can affect nerves’ ability to regulate emotions, blood pressure and bowel movements. Less than 500 patients worldwide suffer from familial dysautonomia, but dysfunctional neural crest cells can cause other disorders, such as facial malformations and an inability to feel pain.
The challenge for scientists has been the fact that by the time a person is born, very few neural crest cells remain, making it hard to study how they cause the various disorders.
To make patient-specific neural crest cells, the team began with laboratory-grown skin cells that had been genetically modified to respond to the presence of the chemical doxycycline by glowing green and turning on the gene Sox10, which guides cells toward maturation as a neural crest cell.
Testing various combinations of molecular signals and watching for telltale green cells, the team found a regimen that turned 2 percent of the cells green. That combination involved turning on Sox10 while growing the cells on a layer of two different proteins and giving them three chemical additives to “rewind” their genetic memory and stimulate a protein network important for development.
Analyzing the green cells at the single cell level, the researchers found that they showed gene activity similar to that of other neural crest cells. Moreover, they discovered that 40 percent were “quad-potent,” or able to become the four cell types typically derived from neural crest cells, while 35 percent were “tri-potent” and could become three of the four. The cells also migrated to the appropriate locations in chick embryos when implanted early in development.
The team then applied a modified version of the technique to skin cells from healthy adults and found that the skin cells became neural crests at a rate similar to the team’s previous experiments.
Finally, the investigators used their regimen on skin cells from patients with familial dysautonomia, then compared these familial dysautonomia-neural crest cells to the control neural crest cells made from healthy adults. They identified 412 genes with lower activity levels in the familial dysautonomia-neural crest cells, of which 98 are involved in processing RNA products made from active genes.
According to the authors, this new observation offers insight into what goes wrong in familial dysautonomia.
“It seems as though the neural crest cells created directly from patient skin cells show more of the characteristics of familial dysautonomia than the neural crest cells we created previously from induced pluripotent stem cells,” says Lee. “That means they should be better predictors of what happens in a particular familial dysautonomia patient, and whether or not a potential treatment will work for any given individual.”
The method they devised should also be applicable to skin cells taken from people with any of the other diseases that result from dysfunctional neural crest cells, such as congenital pain disorders and Charcot-Marie-Tooth diseases, Lee says.
Scientists find potential target for treating mitochondrial disorders
Mitochondria, long known as “cellular power plants” for their generation of the key energy source adenosine triphosphate (ATP), are essential for proper cellular functions. Mitochondrial defects are often observed in a variety of diseases, including cancer, Alzheimer’s disease, and Parkinson’s disease, and are the hallmarks of a number of genetic mitochondrial disorders whose manifestations range from muscle weakness to organ failure. Despite a fairly strong understanding of the pathology of such genetic mitochondrial disorders, efforts to treat them have been largely ineffective.
But now, graduate student Walter Chen and postdoctoral researcher Kivanc Birsoy, both part of Whitehead Institute Member David Sabatini’s lab, have unraveled how to rescue cells suffering from mitochondrial dysfunction, a finding that may lead to new therapies for this condition.
To find genetic mutations that would rescue the cells, Chen and Birsoy mimicked mitochondrial dysfunction in a haploid genetic system developed by former Whitehead Fellow Thijn Brummelkamp. After suppressing mitochondrial function using the drug antimycin, Chen and Birsoy saw that cells with mutations inactivating the gene ATPIF1 were protected against loss of mitochondrial function.
The protein ATPIF1 is part of a backup system to save starving cells. When cells are deprived of oxygen and sugars, a mitochondrial complex that usually produces ATP, called ATP synthase, switches to consuming it, a state that can be harmful to an already starving cell. ATPIF1 interacts with ATP synthase to shut it down and prevent it from consuming the mitochondrion’s dwindling ATP supply but, in the process, also worsens the mitochondrion’s membrane potential.
“In these diseases of mitochondrial dysfunction, in a sense, it’s a false starvation situation for the cell—there are plenty of nutrients, but because there’s a block in the mitochondria’s normal function, the mitochondria behave as if there’s not enough oxygen,” says Chen, who with Birsoy, authored a paper in the journal Cell Reports describing this work. “So in these situations, activation of ATPIF1 is not good, because there are still many nutrients around to provide ATP. Instead, blocking ATPIF1 is therapeutic because it allows for maintenance of the membrane potential.”
Liver cells are frequently affected in patients with severe mitochondrial disease, so Chen and Birsoy tested the effects of mitochondrial dysfunction in the liver cells of control mice and mice with ATPIF1 genetically knocked out. Again, the liver cells with suppressed ATPIF1 function dealt better with mitochondrial dysfunction than liver cells with normal ATPIF1 activity.
“It’s very simple—if you get rid of ATPIF1, you survive in the presence of mitochondrial dysfunction,” says Birsoy. “From what we see so far, there are no major side effects from blocking ATPIF1 in mice.”
For Chen and Birsoy, the next step in this line of research is to test the effects of ATPIF1 suppression in mouse models of mitochondrial dysfunction. Then they will try to identify therapeutics that effectively block ATPIF1 function.
New ideas change your brain cells
A new University of British Columbia study identifies an important molecular change that occurs in the brain when we learn and remember.
Published this month in Nature Neuroscience, the research shows that learning stimulates our brain cells in a manner that causes a small fatty acid to attach to delta-catenin, a protein in the brain. This biochemical modification is essential in producing the changes in brain cell connectivity associated with learning, the study finds.
In animal models, the scientists found almost twice the amount of modified delta-catenin in the brain after learning about new environments. While delta-catenin has previously been linked to learning, this study is the first to describe the protein’s role in the molecular mechanism behind memory formation.
“More work is needed, but this discovery gives us a much better understanding of the tools our brains use to learn and remember, and provides insight into how these processes become disrupted in neurological diseases,” says co-author Shernaz Bamji, an associate professor in UBC’s Life Sciences Institute.
It may also provide an explanation for some mental disabilities, the researchers say. People born without the gene have a severe form of mental retardation called Cri-du-chat syndrome, a rare genetic disorder named for the high-pitched cat-like cry of affected infants. Disruption of the delta-catenin gene has also been observed in some patients with schizophrenia.
“Brain activity can change both the structure of this protein, as well as its function,” says Stefano Brigidi, first author of the article and a PhD candidate Bamji’s laboratory. “When we introduced a mutation that blocked the biochemical modification that occurs in healthy subjects, we abolished the structural changes in brain’s cells that are known to be important for memory formation.”
Background
According to the researchers, more work is needed to fully establish the importance of delta-catenin in building the brain connectivity behind learning and memory. Disruptions to these nerve cell connections are also believed to cause neurodegenerative diseases such as Alzheimer’s and Huntington disease. Understanding the biochemical processes that are important for maintaining these connections may help address the abnormalities in nerve cells that occur in these disease states.
(Image: Shutterstock)
Gender influences symptoms of genetic disorder
A genetic disorder that affects about 1 in every 2,500 births can cause a bewildering array of clinical problems, including brain tumors, impaired vision, learning disabilities, behavioral problems, heart defects and bone deformities. The symptoms and their severity vary among patients affected by this condition, known as neurofibromatosis type 1 (NF1).
Image caption: A mutation in the gene that causes a human condition, neurofibromatosis type 1 (NF1), leads to shorter nerve cell branches (right) in the back of the eyes of female mice. The shorter branches, not seen in male mice with the mutation, make the cells more vulnerable. This may explain why girls with NF1 are more at risk of vision loss from brain tumors. (Credit: David H. Gutmann)
Now, researchers at Washington University School of Medicine in St. Louis have identified a patient’s gender as a clear and simple guidepost to help health-care providers anticipate some of the effects of NF1. The scientists report that girls with NF1 are at greater risk of vision loss from brain tumors. They also identified gender-linked differences in male mice that may help explain why boys with NF1 are more vulnerable to learning disabilities.
“This information will help us adjust our strategies for predicting the potential outcomes in patients with NF1 and recommending appropriate treatments,” said David H. Gutmann, MD, PhD, the Donald O. Schnuck Family Professor of Neurology, who treats NF1 patients at St. Louis Children’s Hospital.
The findings appear online in the Annals of Neurology.
Kelly Diggs-Andrews, PhD, a postdoctoral research associate in Gutmann’s laboratory, reviewed NF1 patient data collected at the Washington University Neurofibromatosis (NF) Center. In her initial assessment, Diggs-Andrews found that the number of boys and girls was almost equal in a group of nearly 100 NF1 patients who had developed brain tumors known as optic gliomas. But vision loss occurred three times more often in girls with these tumors.
With help from David Wozniak, PhD, research professor of psychiatry, the scientists looked for an explanation in Nf1 mice (which, like NF1 patients, have a mutation in their Nf1 gene). They found that more nerve cells died in the eyes of female mice, and they linked the increased cell death to low levels of cyclic AMP, a chemical messenger that plays important roles in nerve function and health in the brain. In addition, Wozniak discovered that only female Nf1 mice had reduced vision, paralleling what was observed in children with NF1.
Two previous studies have shown that boys with NF1 are at higher risk of learning disorders than girls, including spatial learning and memory problems. To look for the causes of this gender-related difference, the scientists first confirmed that Nf1 mice had learning problems by testing the ability of the mice to find a hidden platform after training. After multiple trials, female Nf1 mice quickly found the hidden platform. In striking contrast, the male Nf1 mice did not, revealing that they had deficits in spatial learning and memory.
When the researchers examined the brain regions involved in learning and memory in the Nf1 mice, they identified biochemical abnormalities in the males but not in the females.
“We’re currently working to determine whether differences in the sex hormones are responsible for these abnormalities in vision and memory,” Gutmann said. “We’re talking about a disorder in young kids and in mice, where we normally would not expect sex hormones to play a major role, but we can’t rule them out yet.”
If hormones are responsible for these gender-linked distinctions in NF1, treatments that block hormonal function may be an option for use in patients with NF1, Gutmann added.
“Moreover, these studies identify sex as one important factor that helps to predict clinical outcomes, such as vision loss and problems in cognitive function, in children with NF1,” Gutmann said. “Further understanding of the interplay between sex and NF1 may change the way we manage individuals with this common brain tumor predisposition syndrome.”
(Source: news.wustl.edu)
Zebrafish study paves the way for new treatments for genetic disorder
Scientists from the University of Sheffield have paved the way for new treatments for a common genetic disorder thanks to pioneering research on zebrafish – an animal capable of mending its own heart.
Charcot Marie Tooth disease (CMT) is the most common genetic disorder affecting the nervous system. More than 20,000 people in the UK suffer from CMT, which typically causes progressive weakness and long-term pain in the feet, leading to walking difficulties. There is currently no cure for CMT.
A research project conducted at the Sheffield Institute for Translational Neuroscience (SITraN) and the MRC Centre for Developmental and Biomedical Genetics (CDBG) by Dr Andrew Grierson and his team has revealed that zebrafish could hold the key to finding new therapeutic approaches to treat the condition.
Dr Grierson said: “We have studied zebrafish with a genetic defect that causes CMT in humans. The fish develop normally, but once they reach adulthood they start to develop difficulties swimming.
"By looking at the muscles of these fish we have discovered that the problem lies with the connections between motor neurons and muscle, which are known to be essential for walking in humans and also swimming in fish."
CMT represents a group of neurodegenerative disorders typically characterised by demyelination (CMT1), a process which causes damage to the myelin sheaths that surround our neurons, or distal axon degeneration (CMT2) of motor and sensory neurons. The distal axon is the terminal where neurotransmitter packages within neurons are docked.
The majority of CMT2 cases are caused by mutations in mitofusin 2 (MFN2), which is an essential gene encoding a protein responsible for fusion of the mitochondrial outer membrane. Mitochondria are known as the cellular power plants because they generate most of the supply of adenosine triphosphate (ATP), which is used as a source of chemical energy.
Dr Grierson said: “Previous work on this disorder using mammalian models such as mice has been problematic, because the mitofusin genes are essential for embryonic development. Using zebrafish we were able to develop a model with an adult onset, progressive phenotype with predominant symptoms of motor dysfunction similar to CMT2.
"Motor neurons are the largest cells in our bodies, and as such they are highly dependent on a cellular transport system to deliver molecules through the long nerve cell processes which connect the spinal cord to our muscles. We already know that defects in the cellular transport system occur early in the development of diseases such as Alzheimer’s disease, Motor Neuron Disease and spastic paraplegia. Using our zebrafish model we have found that similar defects in transport are also a key part of the disease process in CMT."
Dr Grierson and his team are now seeking funding to identify new treatments for CMT using the zebrafish model. Because of their size and unique biology, zebrafish are ideal to be used in drug screens for the identification of new therapies for untreatable human conditions.
(Image courtesy: University College London)
What The Human Face Might Look Like 100,000 Years From Now
The human face might look very different in the future.
Artist and researcher Nickolay Lamm from U.K. discount site MyVoucherCodes.co.uk collaborated with a genomics expert to create pictures that show the evolution of the human face 20,000, 60,000, and 100,000 years from now.
In one possible future scenario, humans will have full control of human genome engineering. That is, they will be able to eliminate hereditary genetic disorders, or select desirable genetic traits like straight teeth and natural blonde hair.
Natural human evolution is still at work — the head will get bigger to make room for a larger brain — but most facial features will be molded to reflect what the majority of us perceive as attractive: big eyes, a straight nose, and facial symmetry.
Research unveils insight into a debilitating brain disease
From the neurons that enable thought to the keratinocytes that make toenails grow-a complex canopy of sugar molecules, commonly known as glycans, envelop every living cell in the human body.
These complex carbohydrate chains perform a host of vital functions, providing the necessary machinery for cells to communicate, replicate and survive. It stands to reason, then, that when something goes wrong with a person’s glycans, something goes wrong with them.
Now, researchers at the University of Georgia are learning how changes in normal glycan behavior are related to a rare but fatal lysosomal disease known as Niemann-Pick type C (NPC), a genetic disorder that prevents the body from metabolizing cholesterol properly. The findings were published recently in the PNAS Early Edition.
"We are learning that the problems associated with cholesterol trafficking in the cell lead to problems with glycans on the cell’s surface, and that causes a multitude of negative effects," said Geert-Jan Boons, professor of chemistry in the Franklin College of Arts and Sciences and researcher at UGA’s Complex Carbohydrate Research Center. "Now, for the first time, we can see what these problems are, which we hope will lead to a new understanding of diseases like NPC."
Because NPC patients are unable to metabolize cholesterol, the waxy substance begins to accumulate in the brain. This can lead to a host of serious problems, including neurodegeneration, which the researchers hypothesize may be caused by improper recycling of glycans on the surface of an NPC patient’s cells.
Glycans normally undergo a kind of recycling process when they enter the cell only to be returned to the surface recharged and ready to work. The researchers discovered that glycans in NPC cells do not do this.
"One of the secondary effects of NPC is the disruption of traffic pathways within the cell, and this can lead to altered recycling of glycans," said Richard Steet, associate professor of biochemistry and molecular biology and CCRC researcher. "The glycans come into the cell, but they won’t recycle back up to the cell’s surface where they must exist to function as receptors or ion channels."
"Basically, the machinery gets clogged up," Boons said.
Like downed phone lines and flooded roads in a thunderstorm, glycans get stuck inside the cell making communication and travel for these cells difficult or impossible. Without these basic abilities, the body’s motor, sensory and cognitive functions begin to suffer. This might explain why NPC patients suffer from such a wide variety of neurological and psychiatric disorders, such as uncoordinated limb movements, slurred speech, epilepsy, paralysis, psychosis, dementia and hallucinations.
The researchers made these observations in fibroblasts taken from diseased patients. These cells are most commonly found in connective tissues, and they play a vital role in wound healing. However, they hope to continue their investigation into the effects of NPC by studying glycan behavior in neural cells, which make up the human brain.
While they caution that much more work must be done, they hope that an improved understanding of the roles that glycans play in neural cells will lead to new therapeutics for NPC and other diseases like it.
"It is exciting to work on projects like these, because we believe glycobiology is the next frontier, the next level of complexity," Boons said. "The time is right for new discovery."
(Source: news.uga.edu)
Researchers untangle molecular pathology of giant axonal neuropathy
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.
Fetal healing: Curing congenital diseases in the womb
Our time in the womb is one of the most vulnerable periods of our existence. Pregnant women are warned to steer clear of certain foods and alcohol, and doctors refrain from medical interventions unless absolutely necessary, to avoid the faintest risk of causing birth defects.
Yet it is this very stage that is now being considered for some of the most daring and radical medical procedures yet devised: stem cell and gene therapies. “It’s really the ultimate preventative therapy,” says Alan Flake, a surgeon at the Children’s Hospital of Philadelphia in Pennsylvania. “The idea is to avoid any manifestations of disease.”
The idea may sound alarming, but there is a clear rationale behind it. Use these therapies on an adult, and the body part that you are trying to fix is fully formed. Use them before birth, on the other hand, and you may solve the problem before it even arises. “This will set a new paradigm for treatment of many genetic disorders in future,” says Flake.
Flake has been performing surgery on unborn babies for nearly 30 years, using techniques refined on pregnant animals to ensure they met the challenges of working on tiny bodies and avoided triggering miscarriage. The first operation on a human fetus took place in 1981 to fix a blocked urethra, the tube that carries urine out of the bladder. Since then the field has grown to encompass many types of surgery, such as correction of spinal cord defects to prevent spina bifida.
While fetal surgery may now be mainstream, performing stem cell therapy or gene therapy in the womb would arguably be an order of magnitude more challenging. Yet these techniques seem to represent the future of medicine, offering the chance to vanquish otherwise incurable illnesses by re-engineering the body at the cellular level. Several groups around the world are currently testing them out on animals in the womb.
Of the two, stem cell therapy has the longer history: we have been carrying it out on adults since the 1950s, in the form of bone marrow transplants. Bone marrow contains stem cells that give rise to all the different blood cells, from those that make up the immune system to the oxygen-carrying red blood cells. Bone marrow transplants are mainly carried out to treat cancers of immune cells, such as leukaemia, or the various genetic disorders of red blood cells that give rise to anaemia.
One of Flake’s interests is sickle-cell anaemia, in which red blood cells are distorted into a sickle shape by a mutation in the gene for haemoglobin. People with the condition are usually treated with blood transfusions and drugs to ease the symptoms, but even so they may well die in their 40s or 50s. Some are offered a bone marrow transplant, although perhaps only 1 in 3 can find a donor who is a good match genetically and whose cells are thus unlikely to be rejected by their body. “The biggest issue with treating disease with stem cells is the immune system,” says Flake.
And therein lies the main reason for trying a bone marrow transplant in an unborn baby: its immune system is not fully formed. At around the fourteenth week of pregnancy, the fetus’s immune system learns not to attack its own body by killing off any immune cells that react to the fetus’s own tissues. This raises the prospect of introducing donor stem cells during this learning window and so fooling the immune system into accepting those cells. “You can develop a state of complete tolerance to the donor,” says Flake. “If it works for sickle cell, then there are at least 30 related genetic disorders that could be treated.”
Glowing Vulcan ears reveal brain’s lost neurons
These glowing shapes aren’t the ears of a rave-happy Vulcan - they’re slices from a mouse’s brain.
The slice on the right is from a mouse that lacks a gene called Arl13b - the same gene whose mutation causes Joubert syndrome in humans. This is a rare neurological condition that is linked with autism-spectrum disorders and brain structure malformations.
Without Arl13b, the nerve cells known as interneurons can’t find the right destination in the cerebral cortex during the brain’s development. Since the interneurons don’t end up in the right places, they can’t be wired up properly later on. This causes the disrupted brain development, typical of Joubert syndrome, visible in the image on the right.
The researchers hope that their findings will lead to better treatments for people who have the syndrome.
"Ultimately, if you’re going to come up with therapeutic solutions, it’s important to understand the biology of the disease," says Eva Anton of the University of North Carolina in Chapel Hill, who worked on the research, which was published in Developmental Cell last week.