Researchers at King’s College London and King’s College Hospital, part of King’s Health Partners Academic Health Sciences Centre, have developed a new, non-invasive blood test that can reliably detect whether or not an unborn baby has Down’s syndrome. The test can be given earlier in pregnancy and is more accurate than current checks.
Down’s syndrome, also referred to as trisomy 21, is a genetic disorder caused by the presence of all or part of an extra copy of chromosome 21 in a person’s DNA. Current screening for Down’s syndrome and other trisomy conditions includes a combined test done between the 11th and 13th weeks of pregnancy, which involves an ultrasound screen and a hormonal analysis of the pregnant woman’s blood. Methods such as chorionic villus sampling (CVS), which involves taking cell samples from the placenta, and amniocentesis (using a sample of amniotic fluid), are also used to detect abnormalities but they are both invasive and carry a risk of miscarriage.
Several studies have shown that non-invasive prenatal diagnosis for trisomy syndromes using foetal cell free (cf) DNA from a pregnant woman’s blood is highly sensitive and specific, making it a potentially reliable alternative that can be done earlier in pregnancy.
Kypros Nicolaides, Professor of Fetal Medicine at King’s College London and Head of the Harris Birthright Research Centre for Fetal Medicine at King’s College Hospital, and colleagues have now demonstrated the feasibility of routine screening for trisomies 21, 18, and 13 by cfDNA testing. Testing done in 1005 pregnancies at 10 weeks had a lower false positive rate and higher sensitivity for foetal trisomy than the combined test done at 12 weeks. Both cfDNA and combined testing detected all trisomies, but the estimated false-positive rates were 0.1 percent and 3.4 percent, respectively.
‘This study has shown that the main advantage of cfDNA testing, compared with the combined test, is the substantial reduction in false positive rate. Another major advantage of cfDNA testing is the reporting of results as very high or very low risk, which makes it easier for parents to decide in favour of or against invasive testing,’ said Professor Nicolaides.
A second Ultrasound in Obstetrics & Gynecology study by the group, which included pregnancies undergoing screening at three UK hospitals between March 2006 and May 2012, found that effective first-trimester screening for Down’s syndrome could be achieved by cfDNA testing contingent on the results of the combined test done at 11 to 13 weeks. The strategy detected 98 percent of cases, and invasive testing was needed for confirmation in less than 0.5 percent of cases.
The authors conclude that screening for trisomy 21 by cfDNA testing contingent on the results of an expanded combined test would retain the advantages of the current method of screening, but with a simultaneous major increase in detection rate and decrease in the rate of invasive testing. Kings College London

Problems with a key group of enzymes called topoisomerases can have profound effects on the genetic machinery behind brain development and potentially lead to autism spectrum disorder (ASD), according to research. Scientists at the University of North Carolina School of Medicine have described a finding that represents a significant advance in the hunt for environmental factors behind autism and lends new insights into the disorder’s genetic causes.

‘Our study shows the magnitude of what can happen if topoisomerases are impaired,’ said senior study author Mark Zylka, PhD, associate professor in the Neuroscience Center and the Department of Cell Biology and Physiology at UNC. ‘Inhibiting these enzymes has the potential to profoundly affect neurodevelopment — perhaps even more so than having a mutation in any one of the genes that have been linked to autism.’

The study could have important implications for ASD detection and prevention.

‘This could point to an environmental component to autism,’ said Zylka. ‘A temporary exposure to a topoisomerase inhibitor in utero has the potential to have a long-lasting effect on the brain, by affecting critical periods of brain development. ‘

This study could also explain why some people with mutations in topoisomerases develop autism and other neurodevelopmental disorders.

Topiosomerases are enzymes found in all human cells. Their main function is to untangle DNA when it becomes overwound, a common occurrence that can interfere with key biological processes.

Most of the known topoisomerase-inhibiting chemicals are used as chemotherapy drugs. Zylka said his team is searching for other compounds that have similar effects in nerve cells. ‘If there are additional compounds like this in the environment, then it becomes important to identify them,’ said Zylka. ‘That’s really motivating us to move quickly to identify other drugs or environmental compounds that have similar effects — so that pregnant women can avoid being exposed to these compounds.’

Zylka and his colleagues stumbled upon the discovery quite by accident while studying topotecan, a topoisomerase-inhibiting drug that is used in chemotherapy. Investigating the drug’s effects in mouse and human-derived nerve cells, they noticed that the drug tended to interfere with the proper functioning of genes that were exceptionally long — composed of many DNA base pairs. The group then made the serendipitous connection that many autism-linked genes are extremely long.

‘That’s when we had the ‘Eureka moment,’’ said Zylka. ‘We realised that a lot of the genes that were suppressed were incredibly long autism genes.’

Of the more than 300 genes that are linked to autism, nearly 50 were suppressed by topotecan. Suppressing that many genes across the board — even to a small extent — means a person who is exposed to a topoisomerase inhibitor during brain development could experience neurological effects equivalent to those seen in a person who gets ASD because of a single faulty gene.

The study’s findings could also help lead to a unified theory of how autism-linked genes work. About 20 percent of such genes are connected to synapses — the connections between brain cells. Another 20 percent are related to gene transcription — the process of translating genetic information into biological functions. Zylka said this study bridges those two groups, because it shows that having problems transcribing long synapse genes could impair a person’s ability to construct synapses.

‘Our discovery has the potential to unite these two classes of genes — synaptic genes and transcriptional regulators,’ said Zylka. ‘It could ultimately explain the biological mechanisms behind a large number of autism cases.’ University of North Carolina School of Medicine

Doctors commonly use magnetic resonance imaging (MRI) to diagnose tumours, damage from stroke, and many other medical conditions. Neuroscientists also rely on it as a research tool for identifying parts of the brain that carry out different cognitive functions.

Now, a team of biological engineers at MIT is trying to adapt MRI to a much smaller scale, allowing researchers to visualise gene activity inside the brains of living animals. Tracking these genes with MRI would enable scientists to learn more about how the genes control processes such as forming memories and learning new skills, says Alan Jasanoff, an MIT associate professor of biological engineering and leader of the research team.

‘The dream of molecular imaging is to provide information about the biology of intact organisms, at the molecule level,’ says Jasanoff, who is also an associate member of MIT’s McGovern Institute for Brain Research. ‘The goal is to not have to chop up the brain, but instead to actually see things that are happening inside.’

To help reach that goal, Jasanoff and colleagues have developed a new way to image a ‘reporter gene’ — an artificial gene that turns on or off to signal events in the body, much like an indicator light on a car’s dashboard. In the new study, the reporter gene encodes an enzyme that interacts with a magnetic contrast agent injected into the brain, making the agent visible with MRI. This approach allows researchers to determine when and where that reporter gene is turned on.
MRI uses magnetic fields and radio waves that interact with protons in the body to produce detailed images of the body’s interior. In brain studies, neuroscientists commonly use functional MRI to measure blood flow, which reveals which parts of the brain are active during a particular task. When scanning other organs, doctors sometimes use magnetic ‘contrast agents’ to boost the visibility of certain tissues.

The new MIT approach includes a contrast agent called a manganese porphyrin and the new reporter gene, which codes for a genetically engineered enzyme that alters the electric charge on the contrast agent. Jasanoff and colleagues designed the contrast agent so that it is soluble in water and readily eliminated from the body, making it difficult to detect by MRI. However, when the engineered enzyme, known as SEAP, slices phosphate molecules from the manganese porphyrin, the contrast agent becomes insoluble and starts to accumulate in brain tissues, allowing it to be seen.

The natural version of SEAP is found in the placenta, but not in other tissues. By injecting a virus carrying the SEAP gene into the brain cells of mice, the researchers were able to incorporate the gene into the cells’ own genome. Brain cells then started producing the SEAP protein, which is secreted from the cells and can be anchored to their outer surfaces. That’s important, Jasanoff says, because it means that the contrast agent doesn’t have to penetrate the cells to interact with the enzyme.

Researchers can then find out where SEAP is active by injecting the MRI contrast agent, which spreads throughout the brain but accumulates only near cells producing the SEAP protein.
In this study, which was designed to test this general approach, the detection system revealed only whether the SEAP gene had been successfully incorporated into brain cells. However, in future studies, the researchers intend to engineer the SEAP gene so it is only active when a particular gene of interest is turned on.

Jasanoff first plans to link the SEAP gene with so-called ‘early immediate genes,’ which are necessary for brain plasticity — the weakening and strengthening of connections between neurons, which is essential to learning and memory.

‘As people who are interested in brain function, the top questions we want to address are about how brain function changes patterns of gene expression in the brain,’ Jasanoff says. ‘We also imagine a future where we might turn the reporter enzyme on and off when it binds to neurotransmitters, so we can detect changes in neurotransmitter levels as well.’ MIT

For years, scientists have observed that tumour cells from certain breast cancer patients with aggressive forms of the disease contained low levels of mitochondrial DNA. But, until recently, no one was able to explain how this characteristic influenced disease progression.

Now, University of Pennsylvania researchers have revealed how a reduction in mitochondrial DNA content leads human breast cancer cells to take on aggressive, metastatic properties. The work breaks new ground in understanding why some cancers progress and spread faster than others and may offer clinicians a biomarker that would distinguish patients with particularly aggressive forms of disease, helping personalise treatment approaches.

The study was led by the Penn School of Veterinary Medicine’s Manti Guha, a senior research investigator, and Narayan Avadhani, Harriet Ellison Woodward Professor of Biochemistry in the Department of Animal Biology. Additional Penn Vet collaborators included Satish Srinivasan, Gordon Ruthel, Anna K. Kashina and Thomas Van Winkle. They teamed with Russ P. Carstens of Penn’s Perelman School of Medicine and Arnulfo Mendoza and Chand Khanna of the National Cancer Institute.

Mitochondria, the ‘powerhouses’ of mammalian cells, are also a signalling hub. They are heavily involved in cellular metabolism as well as in apoptosis, the process of programmed cell death by which potentially cancerous cells can be killed before they multiply and spread. In addition, mitochondria contain their own genomes, which code for specific proteins and are expressed in co-ordination with nuclear DNA to regulate the provision of energy to cells.

In mammals, each cell contains between 100 and 1,000 copies of mitochondrial DNA, but previous research had found that as many as 80 percent of people with breast cancer have low mitochondrial DNA, or mtDNA, content.

To gain an understanding of the mechanism that connects low mtDNA levels with a cellular change that leads to cancer and metastasis, Guha, Avadhani and their colleagues set up two systems by which they could purposefully reduce the amount of mtDNA in a cell. One used a chemical to deplete the DNA content, and another altered mtDNA levels genetically. They compared normal, non-cancer-forming human breast tissue cells with cancerous breast cells using both of these treatments, contrasting them with cells with unmanipulated mtDNA.

The differences between cells with unmodified and reduced mtDNA levels were striking, the researchers found. The cells in which mtDNA was reduced had altered metabolism and their structure appeared disorganised, more like that of a metastatic cancer cell. Even the non-tumour-forming breast cells became invasive and more closely resembled cancer cells. Significantly, cells with reduced mtDNA became self-renewing and expressed specific cell surface markers characteristic of breast cancer stem cells.

‘Reducing mitochondrial DNA makes mammary cells look like cancerous stem cells,’ Avadhani said. ‘These cells acquire the characteristics of stem cells, that is the ability to propagate and migrate, in order to begin the process of metastasis and move to distal sites in the body.’

‘Most patients who had low copy numbers of mitochondrial DNA have a poor disease prognosis,’ Guha said. ‘We’ve shown a causal role for this mitochondrial defect and identified a candidate biomarker for aggressive forms of the disease. In the future, mtDNA and the factors involved in mitochondrial signalling may serve as markers of metastatic potential and novel points for therapeutic intervention of cancer stem cells. Since the specific inducers of cancer stem cells, which are key drivers of metastasis, remain elusive, our current findings are a significant advancement in this area.’

No two breast cancers are exactly alike, so having a way to recognise patients who are at high-risk for developing particularly invasive and rapidly metastasising cancers could help physicians customise treatments. In addition, researchers are currently filling in the unknown components of the signalling pathway linking a cell’s mitochondrial DNA levels and its involvement in metastatic disease. University of Pennsylvania

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