Posted in Child Development, Research, Science and Splash, tagged child development, DNA, epidemiology, epigenetics, genetics, inheritance, research on December 4, 2012 |
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Did you happen to see this article in the New York Times: Why Fathers Really Matter. This article introduces the concept of epigenetics. Epigenetics can be defined as “the set of modifications to our genetic material that change the way genes are switched on or off, but which don’t alter the genes themselves.” ¹ Epigenetics helps to explain the relationship between a person’s genotype (the genetic makeup as defined by DNA) and phenotype (physical appearance and traits). The classic example of this is identical twins. Identical twins have identical genotypes but different phenotypes. Their differences become more apparent as they age, because the environment plays an important role in epigenetic modifications. Research in this field is exploding, because herein lies a key to the relationship between an individual’s genetic code, the environment, aging and disease.
It is now known that epigenetic modifications or marks consist of chemical groups that are stuck onto DNA without changing the DNA. They sit on top of the genetic code and control the activation and deactivation of genes. This explains why neurons are so different from skin cells, even though they all contain the same genetic code. If skin cells divide, they become new skin cells. All the genes are deactivated except for the ones needed for the skin cells to look and behave like skin cells.
But epigenetic modification can also be very fluid. These chemical switches on DNA govern protein production—which ones will be produced, when, for how long, how much, etc.
- Think enzymes that control metabolic processes and their impact on health.
- Think hormones and their profound influence on child development.
- Think neurotransmitters that impact learning and the growth of synapses.
In the New York Times article, the author, Judith Shulevitz, describes why she has become obsessed with epigenetics: “because it strikes me as both game-changing and terrifying.” Here are two reasons why:
- Epigenetic mechanisms of gene expression and suppression are influenced by the environment. Our phenotype is not written in the stone of our DNA. Physical traits, mental status, and the development of disease can be shaped by environmental factors such as the food we eat, the air we breathe, our exposure to traumatic events, and our age.
- Epigenetic modifications are heritable. A recent journal article cited over 100 examples of epigenetic inheritance, in both animals and humans.
One of the best known example of both of these principles of epigenetics in humans is an epidemiological study of the people living through the “Dutch Hunger Winter” of 1944-45, during which over 20,000 people died of starvation. Scientists were able to evaluate the long-term effects of the famine among the survivors, including pregnant women and their children. If a woman was well nourished during the first portion of her pregnancy but malnourished for the last few months, her baby was likely to have a lower birth weight. On the other hand, if the baby was conceived towards the end of the famine and the mother was malnourished only during the first trimester, she was likely to have a normal birth weight baby. This is not surprising, because babies do most of their growing during the last months of a pregnancy. But long-term effects were very surprising. The babies that were born small stayed small for the rest of their lives, with lower obesity rates than the general population (Audrey Hepburn was one of these babies). The normal birth weight babies who were poorly nourished during the first trimester were more likely to become obese as adults. A major environmental event (the famine) changed the epigenetic programming of the developing fetus. The epigenetic modifications of the babies that were malnourished during the first trimester enabled them to survive by making the most of a bad situation. But this reprogramming remained in effect long after the famine that caused it. It is thought that epigenetic modifications to the genes regulating metabolism resulted in a greater likelihood of becoming obese. Even more extraordinary was the presence of these effects in future generations. The grandchildren were more likely to be skinny or obese. Something that happened to a population of pregnant women affected their children and their children’s children!
While Shulevitz has chosen to describe epigenetics as “game-changing and terrifying,” others view epigenetics as the new frontier in fighting disease. Epigenetic therapies are already being used to fight various cancers. The role of epigenetics in depression, autism, Alzheimer’s disease and addiction are being explored. An understanding of epigenetics may prepare us to face the global obesity epidemic. The epigenetics revolution is underway, and the implications for patient care today and tomorrow are profound.
1. Carey N. The Epigenetics Revolution: How Modern Biology is Rewriting Our Understanding of Genetics, Disease and Inheritance. Columbia University Press: 2012.
[i] Carey N. The Epigenetics Revolution. 2012
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A shout out to COVD members Jeffrey Cooper and Erica Schulman! Drs. Cooper, Schulman and Jamal just published a review of the development and treatment of myopia. This evidence-based review of over 200 articles has really got me thinking about the options in treating myopia (nearsightedness).
New theories on the development of myopia are evaluating the role of peripheral retina. When lenses are prescribed for any type of refractive error (myopia, hyperopia, astigmatism), those lenses put a clear and focused image on the fovea, which is essentially the “bullseye” on the retina. Whenever we want to see something clearly, we aim our eyes so the image falls on the fovea. The lenses allow us to see clearly precisely because the image is focused on the fovea. But those lenses (especially spectacles) have a different curvature than the retina. The result is a slight defocus on the peripheral retina. The further away from the central retina you are, the greater the amount of defocus. This is not something noticeable by the average patient, because the amount of blur is small, and because we don’t notice blur as well in the periphery. But it seems that our retinas DO notice, because there is significant evidence that this peripheral defocus drives the eye to elongate, and that elongation results in myopia.
Consideration of this body of evidence has resulted in renewed interest in the clinical use of orthokeratology – Ortho-K (aka corneal reshaping therapy or CRT) to reduce myopia progression. In addition to putting a clear and focused image on the fovea, orthokeratology fitted contact lenses flatten the central cornea which results in a steepening of the peripheral cornea. The end result is a reduction in the peripheral defocus on the retina, and therefore a reduction in the drive toward elongation of the eyeball.
After reviewing all the studies investigating Ortho-K and the progression of myopia conducted in the last 12 years, the authors conclude: “Ortho-K results in an approximately 40% reduction in the progression of myopia. Its advantages are that it both eliminates the need for daytime contact lens wear and reduces the progression of myopia. Its disadvantages include cost, risk of infection, discomfort, problems with insertion and removal, and reduced visual acuity as compared to glasses or daily wear contact lenses. In addition it is difficult to determine which subjects will demonstrate slowing of their myopia and by how much.”
Once again, the science is catching up to clinical practice. Many developmental optometrists have been aggressively using Ortho-K as one of the possible treatments to slow the progression of myopia. Renewed interest in the role of peripheral retina in the progression of myopia will lead to more research and more research will lead to better clinical guidelines in the use of Ortho-K. Developmental optometrists are sure to be at the forefront when putting the evidence into clinical practice.
Read more about Ortho-K here.
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Posted in Amblyopia, Brain Plasticity, Research, Vision Therapy, tagged Amblyopia, dark exposure, Dr. Dennis Levi, Dr. Elizabeth Quinlan, neuroplasticity, research on October 30, 2012 |
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Amblyopia therapy –” it’s no longer just for kids.” These are the words used by Dr. Michael DePaolis in a recent editorial in Primary Care Optometry News. He describes a big moment in optometry, a paradigm shift in patient care. New research has made it very clear that neuroplasticity in the adult brain is alive and well, and the implications reach far beyond the treatment of amblyopia. But let’s start with amblyopia.
Dr. Dennis Levi explored the use of action video games to treat adults with amblyopia. Why would playing action video games be an effective treatment of amblyopia? “Action game play is extremely varied in its demands and rich in the set of visual experiences it offers. Thus…. the very act of action game playing seems to train the brain to learn, on the fly, how to make the best use of the available information in the display, independent of the specifics of this display, allowing for the broad transfer of learning.” Levi had 20 amblyopic adults play action video games with only their amblyopic eye. All 20 subjects improved. Levi speculates that video game playing is “arousing and rewarding.” Neurotransmitters such as acetylcholine and dopamine are released, and these neurotransmitters are associated with enhanced neuroplasticity. Compliance is also enhanced, because action video games are more interesting and fun to play than many traditional vision therapy activities.
Now consider some incredible research by Dr. Elizabeth Quinlan. Dr. Quinlan’s presentation at COVD’s annual meeting focused on the treatment of amblyopia, specifically on possible mechanisms to enhance neuroplasticity. She has been recording the electrical response of the part of the brain associated with vision (aka the visual cortex) resulting from different types of visual stimulation. In one series of experiments, she created amblyopic animals (in this case, amblyopic rats) by occluding one eye for an extended period of time. The resulting pattern of visually evoked potentials from portions of the visual cortex was significantly altered in a pattern that reflected the lack of visual input from the occluded eye. When the occlusion was ended and the animals had a chance to receive normal visual experience, this pattern of altered electrical activity in the brains of the rats did not improve. In other words, there was no neurophysiological recovery when normal visual experience was restored. That is, there was no neurophysiological recovery until she put these animals in the dark. After placing these animals in total darkness for 3-10 days, and then providing a short period of “rat vision therapy,” these rats had a complete neurophysiological recovery. The visual evoked responses from the visual cortex demonstrated a more balanced input from each eye. The dark exposure enhanced the neuroplasticity of the visual cortex which is the basis for successful treatment of amblyopia.
Are we ready for another paradigm shift in the treatment of amblyopia? Of course, this research was done with rats and involved recording electrical activity from electrodes placed into their visual cortex. That is a very long way from clinical trials that might provide evidence of more effective treatment of amblyopia by enhancing neuroplasticity in the human brain after dark exposure. But I cannot help but wonder …… can we provide a safe environment of total darkness for adult patients to enhance their neuroplasticity and then provide vision therapy programs that utilize action video games? who will open the first Hotel Amblyopia?
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Dr. Sue Barry was recently interviewed by NPR for their NOVA web series called “The Secret Life of Scientists and Engineers.” Her experiences with vision therapy and learning to see in 3-D were life-changing. Neuroplasticity is the mechanism through which we CAN get better at everything. Anyone. Any age.
Watch Dr. Sue Barry: The Secret Life of Scientists
Read more about neuroplasticity here and here.
Then watch Dr. Barry tell a joke.
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