The Genetic of Autism

July 17, 2015

By Medical Discovery News

The Genetics of Autism

In the past decade, autism has garnered a lot of media attention. Lately much of the focus has been on finding the cause. Much is still a mystery, despite confirming that vaccines and parenting are not responsible. Now a new study of twins has given us another clue, revealing that the influence of genetics on the development of autism may be between 56 and 95 percent.

According to the Centers for Disease Control, one in 68 children have autism, a neurodegenerative disorder that exists on a spectrum, meaning its symptoms and their severity varies tremendously. A hallmark feature of autism is impaired social interaction, noticeable even in babies. Those with autism find it difficult to interpret what others are thinking or feeling because they miss the social clues most take for granted. Other symptoms can include repetitive movements such as spinning or rocking, speech delays, and self-destructive behaviors. Children with autism can also have a variety of other conditions including epilepsy, Tourette’s syndrome, learning disabilities, and attention deficit disorder (ADD).

The cause of autism is probably rooted in genetics and environment. Comparing sets of twins is a well-established way of clarifying the extent of both these influences. Scientists in London studied over 6,400 pairs of twins in England and Wales between 1994 and 1996, all raised by their parents in the same environments. The data they collected revealed that the chance of identical twins having autism was 77-99 percent, whereas the chance of non-identical twins having autism was 22-65 percent. This suggests that additive genetic factors contribute to 56-95 percent of autism cases. This is far higher than previous estimates, which assumed environmental influences were more of a factor.

While no one gene has been attributed to autism, the majority of the genes that are associated seem to be linked to one specific symptom. For example, the gene EN2 is often studied for its role in autism because it is critical to midbrain and cerebellum development. Reelin, a protein found mainly in the brain, also plays an important role in autism development. In adults, reelin is important to learning and memory and is critical to inducing and maintaining long-term neuronal connections. Autistic individuals consistently show elevated levels of serotonin, otherwise known as the feel-good hormone. This has led researchers to examine the role of genes involved in serotonin regulation as potential causes of autism. Another hormone system called arginine-vasopressin affects social behavior, so one of the genes that regulates it is a candidate for autism as well. These are just a few of the many genes being studied.

As more people become aware of autism and more children are diagnosed, the pressure is building to further understand this disorder. Discovering the causes might translate to better diagnostics and treatment for autism.

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Autism on the Increase

Nov. 28, 2014

By Medical Discovery News

Autism on the Increase

Based on statistics, you probably know someone with a form of autism. Autism rates in America grew by 30 percent from 2008-2010 and have doubled since 2000. Now, one in 68 eight-year-olds are diagnosed with autism. On average, one child in each grade of every elementary school has autism.

What is responsible for the remarkable rise of this disease? Perhaps we have gotten better at diagnosing it. Now, research is working to establish how autism occurs, even before birth, and how to diagnosis it sooner.

Autism is actually not a single disease but a spectrum of disorders. It is clearly related to infant development and is caused by differences in the brain. There are multiple causes of autism, but most are not yet known. One possible connection is that people tend to conceive later. The age at which women give birth has been increasing for many years and is linked to higher chances of autism.

Diagnosis of autism spectrum disorders (ASD) relies on observing differences in a person’s communication, social skills, and typical behavior. Roughly one-third of those with autism are also diagnosed with intellectual deficits, but the remaining two-third have normal or above average intelligence. Most are diagnosed at four years old but some are identified by age two. This is critical because research has repeatedly shown that the earlier therapy starts, the more likely it will result in substantial improvement.

A new study published in the “New England Journal of Medicine” suggests that ASD begins long before birth. This study documented changes in the cerebral cortex, which is the outermost layer of the brain. Almost 90 percent of children with autism had abnormal developments of their cerebral cortexes, centered in regions associated with social and emotional communication and language. These changes appeared as patches in the brain, suggesting that they occur during the child’s development in the womb. This may also explain why early interventions are more effective, as the brain is still developing. Currently, there is no way to spot these patches appearing on the cortex during gestation or in infants, but it could be an area of future research.

However, another study, reported in the journal “Nature,” suggests that eye-tracking technology can detect autism in two- to six-month-old children. This technology looks at the ability of babies to make eye contact with adults. Those with autism show a steady decline in eye contact starting at two to six months of age. This seemingly simple behavior is actually quite complex and difficult to quantitate, requiring sophisticated video technology. Such eye movements are not noticeable to parents. If larger studies prove successful, this may become a way to screen infants for autism and begin therapy as soon as possible.

Autism will continue to make headlines as a leading childhood health concern. As always, if you have concerns about your child’s activity, speech, or social interactions, talk with your pediatrician.

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Does Grey Matter?

Aug. 8, 2014

By Medical Discovery News

The brain

What do brain scientists and fans of E. L. James have in common? They are both passionate about shades of grey. Results from a recent study in the scientific journal “Molecular Psychiatry” indicate that grey matter really does, well, matter. This study shows that the thickness of grey matter in the brain may be linked to intelligence and may also explain why some people have learning difficulties.

Grey matter is the outermost region of the brain, a layer of tissue two to four millimeters thick covering the brain on both sides with a wrinkled surface. Underneath the grey matter, also called the cerebral cortex, is the white matter of the brain, the cerebrum.

Grey matter is responsible for some major human functions including awareness, attention, consciousness, language, thought, and memory. Previous studies have shown that animals with bigger brains generally have thicker cortexes, but there has not been a strict link between intelligence and the thickness of the grey matter until now. 

For this new study, researchers at King’s College London’s Institute of Psychiatry obtained brain scans and DNA samples from 1,583 14-year-olds. They also tested the verbal and nonverbal intelligence of these subjects. Using DNA analysis, scientists looked for gene variants that could be responsible for the intelligence differences of this group. This proved to be a daunting task as they discovered more than 50,000 gene variants associated with brain development. However, with the help of computation biology, researchers uncovered some astounding results. Those with one particular gene variant caused by a single nucleotide polymorphism (or change) had thinner grey matter on the left side of their brains. And, these same individuals tested lower on the intelligence tests. 

Called NPTN, this gene encodes a protein that works in brain cells called neurons. The variant of NPTN affects communication between neurons in the brain, thereby explaining its impact on important functions of grey matter. Additional experiments suggest the NPTN variant may have more of an effect in the left side of the brain than the right side. This may correlate to lower intelligence due to the function of this important gene and its encoded protein in the left brain. 

While important, NPTN is not the only thing that determines intelligence – a multitude of other genes and environmental influences are clearly involved as well. However, this gene may provide new clues as to how intelligence is built in humans. Also, it will be interesting to see if this gene variant is associated with cognitive diseases like autism or psychological disorders like schizophrenia. 

Thanks to the new B.R.A.I.N. initiative that funds basic and translational research, we look forward to better understanding the human brain, arguably one of the most important human organs we know the least about. 

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That’s An A

March 8, 2013

By Medical Discovery News

The composer Wolfgang Amadeus Mozart could hear a single, isolated musical note and identify what note it was, such as an “A,” by sound alone. What’s more, he could sing the sound of a single note at will. He had absolute pitch or perfect pitch, the ability to identify and even echo a particular note without any help. 

Perfect pitch is a relatively rare ability that occurs in as few as one in 10,000 people and almost always among those who have had musical training before the age of seven. Michael Jackson, Mariah Carey, Ella Fitzgerald, Bing Crosby, Frank Sinatra, and Jimi Hendrix all displayed this ability. However, musical training alone is not enough to develop perfect pitch. Many with such training, even professional musicians, do not have perfect pitch. Tchaikovsky, Wagner, Leonard Bernstein, and Julie Andrews made do with relative pitch, the ability to define a note  with the help of a reference like a tuning fork. 

Perfect pitch appears to occur in families and recent as well as ongoing research suggests it can be inherited. A person who has a sibling with perfect pitch and early musical training is 15 times more likely to possess perfect pitch than someone with just musical training and no family history.

A study at the University of California San Francisco with over 2,000 subjects revealed that a person either has perfect pitch or not; there is no scale of ability in identifying pitches. Using DNA from 73 families, the research team attempted to identify which areas of the human genome are related to the inheritance of perfect pitch. Surprisingly, the genetic information they found was not located in the same place for every person who possesses perfect pitch. For example, in families of mixed European heritage, this genetic information is carried in a region on chromosome 8 called 8q24.21, which is essentially an address describing a gene location.

But in families of East Asian descent and in a small group of Ashkenazi Jewish families who have a higher incidence of perfect pitch than the general population, this genetic information was located on a completely different chromosome, with the address 7q22.3. Since perfect pitch can be inherited through different locations on genome, researchers are now sequencing DNA to discover all the genes associated with perfect pitch.

Another study in Denmark questioned whether a link exists between perfect pitch and autism, since those with sensory and developmental disorders have a higher incidence of the ability. While smaller in scale than the study in California, researchers did find that those with perfect pitch scored significantly higher on the autism spectrum than those without.

In another recent study those with perfect pitch had greater than usual abilities for remembering spoken sounds. When they were told a long series of numbers and asked to remember them, those with perfect pitch remembered many more of those numbers than those without perfect pitch. But when they were given a series of numbers visually, those with perfect pitch remembered about the same as those without. Therefore, some argue that perfect pitch is a way of recognizing sounds rather than a musical ability and can therefore be learned. They believe that while certain gene variants may help people acquire perfect pitch, almost anyone can be trained to label notes as long as they start young.

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Fishing for Answers

By Medical Discovery News

Dec. 8, 2012

Image

The stereotypical picture of a scientist includes a white lab coat and a laboratory full of petri dishes, beakers, and test tubes. However, some research questions can only be answered using the complexity of living, breathing multicellular organisms. In these cases, preliminary studies use animal models, and if successful, the final stages of development for a new drug or therapy are conducted using human subjects.

Today, scientists are using a certain animal more extensively in order to understand human disease. The Zebrafish is a small torpedo-shaped fish native to the Indian subcontinent. It’s named for its distinctive horizontal striping pattern of alternating gold or silver and blues stripes.

While it looks nothing like a human, this fish is actually a great model for studying aspects of human disease. Its genome has been completely sequenced, it matures quickly, its genes can be manipulated, and its embryos are transparent. These characteristics make the Zebrafish a highly used and valuable model for genetic and developmental studies.

Two recent reports illustrate the usefulness of the Zebrafish. In one study, scientists examined the role of a human gene called SETDB1 on the progression of a human cancer called melanoma, an aggressive and deadly skin cancer that is responsible for almost 9,000 deaths in the U.S. each year.

Scientists introduced a copy of the SETDB1 gene into Zebrafish embryos, which grew to carry the gene in cells called melanocytes. Then, SETDB1 genes methylated proteins in chromatin, a process that prevents other genes from activating and functioning correctly.

By doing so, SETDB1 accelerates the growth and spread of melanoma. Scientists think that SETDB1 works the same way in humans, so future trials will target this gene and hopefully limit the development of melanoma.

In the second study, a group of scientists used Zebrafish to study human genes thought to contribute to the genetic basis of Autism Spectrum Disorders. While fish aren’t autistic, the scientists aimed to identify the specific genes involved so future therapies could control those genes and therefore the disorder.

The research focused on about 24 genes in a specific genetic region known as 19p11.2 that are known to be missing or duplicated in some autistic patients. One at a time, scientists deleted these genes in Zebrafish embryos and examined the brain abnormalities that resulted, such as changes in the anatomy of brain tissue and the structure of axons that provide the wiring to transmit signals to brain cells called neurons.

Next, they reduced the genes’ production of proteins by 50 percent, which is more like what happens in humans. Two genes continued to lead to abnormal Zebrafish brain development, giving researchers two new targets for treatments that could help those with autism.

So a lowly fish from halfway across the world now plays an irreplaceable role in understanding and treating human disease.

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