Posts tagged genetics

ScienceDaily (Aug. 27, 2012) — Muscular dystrophy is a complicated set of genetic diseases in which genetic mutations affect the various proteins that contribute to a complex that is required for a structural bridge between muscle cells and the extracellular matrix (ECM) that provides the physical and chemical environment required for their development and function.

The affects of these genetic mutations in patients vary widely, even when the same gene is affected. In order to develop treatments for this disease, it is important to have an animal model that accurately reflects the course of the disease in humans. In this issue of the Journal of Clinical Investigation, researchers at the University of Iowa report the development of a mouse model of Fukuyama’s muscular dystrophy that copies the pathology seen in the human form of the disease.

By removing the gene fukutin from mouse embryos at various points during development, researchers led by Kevin Campbell were able to determine that fukutin disrupts important modifications of dystrophin that prevent the muscle cells from attaching to the ECM. Disruption of the gene earlier in development led to a more severe form of the disease, suggesting that fukutin is important for muscle maturation. Disruptions in later stages of development caused a less severe form of the disease. In a companion piece, Elizabeth McNally of the University of Chicago discusses the implications of this disease model for the development of new therapies to treat muscular dystrophy.

Source: Science Daily

August 26, 2012

Vitamin B12 is essential to human health. However, some people have inherited conditions that leave them unable to process vitamin B12. As a result they are prone to serious health problems, including developmental delay, psychosis, stroke and dementia. An international research team recently discovered a new genetic disease related to vitamin B12 deficiency by identifying a gene that is vital to the transport of vitamin into the cells of the body. This discovery will help doctors better diagnose this rare genetic disorder and open the door to new treatments. The findings are published in the journal Nature Genetics.

"We found that a second transport protein was involved in the uptake of the vitamin into the cells, thus providing evidence of another cause of hereditary vitamin B12 deficiency", said Dr. David Rosenblatt, one of the study’s co-authors, scientist in medical genetics and genomics at the Research Institute of the McGill University Health Centre (RI MUHC) and Dodd Q. Chu and Family Chair in Medical Genetics and the Chair of the Department of Human Genetics at McGill University. "It is also the first description of a new genetic disease associated with how vitamin B12 is handled by the body".

These results build on previous research by the same team from the RI MUHC and McGill University, with their colleagues in Switzerland, Germany and the United States. In previous work, the researchers discovered that vitamin B12 enters our cells with help from of a specific transport protein. In this study, they were working independently with two patients showing symptoms of the cblF gene defect of vitamin B12 metabolism but without an actual defect in this gene. Their work led to the discovery of a new gene, ABCD4, associated with the transport of B12 and responsible for a new disease called cblJ combined homocystinuria and methylmalonic aciduria (cblJ-Hcy-MMA).

Using next generation sequencing of the patients’ genetic information, the scientists identified two mutations in the same ABCD4 gene, in both patients. “We were also able to compensate for the genetic mutation by adding an intact ABCD4 protein to the patients’ cells, thus allowing the vitamin to be properly integrated into the cells,” explained Dr. Matthias Baumgartner, senior author of the study and a Professor of metabolic diseases at Zurich’s University Children’s Hospital.

Vitamin B12, or cobalamin, is essential for healthy functioning of the human nervous system and red blood cell synthesis. Unable to produce the vitamin itself, the human body has to obtain it from animal-based foods such as milk products, eggs, red meat, chicken, fish, and shellfish – or vitamin supplements. Vitamin B12 is not found in vegetables.

"This discovery will lead to the early diagnosis of this serious genetic disorder and has given us new paths to explore treatment options. It also helps explain how vitamin B12 functions in the body, even for those without the disorder," said Dr. Rosenblatt who is the director of one of only two referral laboratories in the world for patients suspected of having this genetic inability to absorb vitamin B12. Dr. Rosenblatt points out that the study of patients with rare diseases is essential to the advancement of our knowledge of human biology.

Source: medicalxpress.com

Better diagnosis and treatment of a crippling inherited nerve disorder may be just around the corner thanks to an international team that spanned Asia, Europe and the United States. The team had been hunting DNA strands for the cause of the inherited nerve disorder known as spinocerebellar ataxia, or SCA. The disease causes progressive loss of balance, muscle control and ability to walk. Thanks to their diligence and detective work they have discovered the disease gene in a region of chromosome 1 where another group from the Netherlands had previously shown linkage with a form of SCA called SCA19, and the Taiwanese group on the new paper had shown similar linkage in a family for a form of the disease that was then called SCA22. The international team, from France, Japan, Taiwan and the USA have published their discovery in the Annals of Neurology. The Dutch group has also published results in the same issue of the journal.

Their paper reveals that mutations in the gene KCND3 were found in six families in Asia, Europe and the United States that have been haunted by SCA. Their results will allow for a better understanding of why nerves in the brain’s movement-controlling centre die, and how new DNA mapping techniques can find the causes of other diseases that run in families.

Margit Burmeister, Ph.D., a geneticist at University of Michigan Health System (U-M), helped lead the work and stressed that the gene could not have been found without a great deal of DNA detective work and the cooperation of the families who volunteered to let researchers map all the DNA of multiple members of their family tree. ‘We combined traditional genetic linkage analysis in families with inherited diseases with whole exome sequencing of an individual’s DNA, allowing us to narrow down and ultimately identify the mutation,’ she says. ‘This new type of approach has already resulted in many new gene identifications, and will bring in many more.’

The gene is very important as it manages the production of a protein that allows nerve cells to ‘talk’ to one another through the flow of potassium. Pinpointing its role as a cause of ataxia will now allow more people with ataxia to learn the exact cause of their disease, give a very specific target for new treatments, and perhaps allow the families to stop the disease from affecting future generations.

U-M neurologist Vikram Shakkottai, M.D., Ph.D., an ataxia specialist and co-author on the paper, also notes that the new genetic information will help patients find out the specific cause of their disease. He and his colleagues are already working to find drugs that might alter potassium flow, and provide a treatment for a group of diseases that currently are only treated with supportive care such as physical activity and balance training as patients deteriorate. ‘Many of the families who come to our clinic for treatment don’t have a recognised genetic mutation, so it’s important to find new genetic mutations to explain their symptoms,’ says Shakkottai. ‘But at the same time, this research is helping us understand a common mechanism of nerve cell dysfunction in progressive and non-progressive disease.’

Their findings however are not restricted to just ataxia. The researchers were also able to show that when KCND3 is mutated, it causes poor communication between nerve cells in the cerebellum as well as the death of those cells. This discovery could aid research on other neurological disorders involving balance and movement.

The Dutch team, that also published its findings about KCND3 at the same time, studied families in the Netherlands and found that mutations on the gene are responsible for SCA19, the cause of which had up until now been a mystery. ‘In other words, mutations in this gene are not uncommon and present all over the world,’ says Burmeister. ‘This means that in the future, this gene should be tested for mutations as part of a clinical genetic test panel for patients with ataxia symptoms. Because a generation can be skipped, it may even be relevant in some sporadic cases - those where the patient isn’t aware of any other family members with a similar disease.’

Source: Cordis News

22 August 2012

Scientists have found a switch in the brain which may explain why smoking cannabis causes psychosis and addiction in more than one-in-ten users.

The team, at Aberdeen University found a genetic difference in the switch, probably inherited from early humans who smoked the drug in prehistoric times. The difference may also explain why some people could be more susceptible to conditions such as obesity.

The researchers, at the university’s Kosterlitz Centre for Therapeutics, studied genetic differences around a gene called ‘CNR1’, which produces what are known as cannabinoid receptors in the brain which control parts of the brain involved in memory, mood, appetite and pain.

Cannabinoid receptors activate these areas of the brain when they are triggered by naturally-occurring chemicals in the body known as endocannabinoids. Chemicals found in the cannabis and ‘skunk’ mimic the action of endocannabinoids. It is known that cannabis has pain-relieving and anti-inflammatory properties which can help treat diseases such as multiple sclerosis and arthritis.

However, developing drugs from cannabis to treat these conditions is hampered by the fact that such drugs will have psychoactive side effects - and smoked cannabis can cause addiction and psychosis in up to 12 per cent of users.

Dr Alasdair MacKenzie, who led the research, said:

We looked at one specific genetic difference in CNR1 because we know it is linked to obesity and addiction. What we found was a mutation that caused a change in the genetic switch for the gene itself - a switch that is very ancient and has remained relatively unchanged in over three hundred million years of evolution, since before the time of the dinosaurs.

These genetic ‘switches’ regulate the gene itself, ensuring that it is turned on or off in the right place at the right time and in the right amount. It is normally thought that mutations cause disease by reducing the function of the gene, or the switch that controls it. In this case however, the mutation actually increased the activity of the switch in parts of the brain that control appetite and pain, and also, and most especially, in the part of the brain called the hippocampus, which is affected in psychosis.

He added: We know that this overactive switch is relatively rare in Europeans, but is quite common in African populations. But we were all once African, so something must have decreased it in our early ancestors who left Africa and migrated through Central Asia towards Europe and the north. One possibility we are keen to explore is that once in Central Asia these early migrants came into contact with the cannabis plant, which we know was endemic across that area at that time.

It is possible that the side effects of taking cannabis were such that people with the mutation were not so effective in producing and raising children. Therefore, over the generations the numbers of people with the mutation decreased.

This work is at a very early stage however, and there are likely to be more exciting discoveries - not only on how these differences came about, but also about the role of this genetic switch in health and disease.

Co-researcher Dr Scott Davidson said: Further analysis of this mutation will help us to understand many of the side effects which are associated with cannabis use such as addiction and psychosis.

Professor Ruth Ross, head of the Kosterlitz Centre, an internationally recognised expert in cannabis pharmacology, said: Previously in drug research, attempts to detect the causes of adverse drug reactions have focused on the genes themselves.

Our study is one of the first to explore the possibility that changes in gene switches are involved in causing side effects to drugs. We believe this approach will be crucially important in the future development of more effective personalised medicine, with fewer side effects.

One question that is intriguing the research team is why this overactive genetic switch evolved in the first place.

(Source: Daily Mail)

22 August 2012 by Ewen Callaway

Genome study may explain links between paternal age and conditions such as autism.

Older fathers’ sperm have more mutations — as do their children.
V. Peñafiel/Flickr/GETTY

In the 1930s, the pioneering geneticist J. B. S. Haldane noticed a peculiar inheritance pattern in families with long histories of haemophilia. The faulty mutation responsible for the blood-clotting disorder tended to arise on the X chromosomes that fathers passed to their daughters, rather than on those that mothers passed down. Haldane subsequently proposed that children inherit more mutations from their fathers than their mothers, although he acknowledged that “it is difficult to see how this could be proved or disproved for many years to come”.

(Source: nature.com)

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ScienceDaily (Aug. 22, 2012) — A low dose of the sedative clonazepam alleviated autistic-like behavior in mice with a mutation that causes Dravet syndrome in humans, University of Washington researchers have shown.

(Credit: © Vasiliy Koval / Fotolia)

Dravet syndrome is an infant seizure disorder accompanied by developmental delays and behavioral symptoms that include autistic features. It usually originates spontaneously from a gene mutation in an affected child not found in either parent.

Studies of mice with a similar gene mutation are revealing the overly excited brain circuits behind the autistic traits and cognitive impairments common in this condition. The research report appears in the Aug. 23 issue of Nature. Dr William Catterall, professor and chair of pharmacology at the UW, is the senior author.

Dravet syndrome mutations cause loss-of-function of the human gene called SCN1A. People or mice with two copies of the mutation do not survive infancy; one copy results in major disability and sometimes early death. The mutation causes malformation in one type of sodium ion channels, the tiny pores in nerve cells that produce electrical signals by gating the flow of sodium ions.

The Catteralll lab is studying these defective ion channels and their repercussion on cell-to-cell signaling in the brain. They also are documenting the behavior of mice with this mutation, compared to their unaffected peers. Their findings may help explain how the sporadic gene mutations that cause Dravet syndrome lead to its symptoms of cognitive deficit and autistic behaviors.

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21 August 2012 by Lois Rogers

Thousands of otherwise healthy people put up with a level of sleep deprivation that would drive the rest of us insane. But they are not the usual candidates for insomnia, such as shift workers or those with severe mental illness. Instead, they belong to a newly identified group of people born without the ‘comfort’ genes needed for easy sleep.

This means they are immune to the feeling of warmth and relaxation which sends an average person off to sleep within 15 minutes. Their genes are designed instead to maintain a state of mental alertness. This makes normal, prolonged sleep impossible so they sleep fitfully, in only short bursts. Even then, their lack of ‘comfort’ genes may mean they struggle to get comfortable, fussing about the bedding or finding their sleeping position.

There are other so-called insomnia genes — some cause repeated periods of wakefulness in the small hours of the night or at the slightest disturbance, or drive an affected person to leap out of bed raring to start the day at 4am, but leave them exhausted by 4pm. Until recently, insomnia was considered a purely psychological complaint triggered by stress, grief, or sleep disruption as a result of shift work or jet lag.

But doctors are now unravelling the genetic explanation of why at least one-third of us have intermittent or constant sleep problems. Even so, it’s already thought there could be six or more different types of insomnia linked to genes. This means it will be possible to develop drugs to block the effect of the chemical signals they produce.

(Source: Daily Mail)

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