The science of epigenetics and DNA

Genetics

Many genetic hallmarks were set before you were born, but the science of epigenetics shows that even adults can alter their DNA. muse editor Rebecca Long explores the different types of genetic make ups and what you can control.

Most of what is outwardly expressed by your genetic code was hardwired long before you were sticking Vita-Weats in the VHS. Intelligence, how well you handle stress, whether you’ll be doing Sudoku into your 90s and susceptibility to mental illness are all thought to be somewhat predetermined and documented in a kind of genetic game plan. But in the past few years, research involving over 400 scientists from across the globe has revealed holes in the blueprint theory, suggesting that we have greater control over how our code is expressed than previously thought.

According to the decade-long Encode project, around four million ‘switches’ science had written off as ‘genetic garbage’ could actually be integral to how cells and tissues behave. The discovery paves the way for DNA tweaks that could avert everything from wrinkles to food intolerance and even certain cancers according to research papers published in the journal, Nature.

“There are a lot more things happening than we expected,” said Ewan Birney, a lead researcher in the Encode project.

The theory that we don’t need to stand by and accept the hand dealt by DNA strands – which comprise around 23,000 genes – isn’t entirely new. The progressive scientific fields of epigenetics, epigenomics, and nutrigenomics suggest that circumventing destiny can be as simple as changing your diet and avoiding certain chemicals.

Think of DNA, or deoxyribonucleic acid, as an iPhone. The intricate chemical codes surrounding DNA and known as ‘epigenomes’ are the plan terms issued by your carrier (say, how much data you can use before you’re charged 10 bucks for an extra gig). Extrapolate the telco analogy to twins, and it makes sense that even siblings sharing a genetic profile can have different health outcomes. While identical twins have identical operating systems (known in genetic circles as genomes), how they operate is influenced by environmental factors. Hello, $79 plan.

Scientists who studied genomes in twins at Sydney’s Garvan Institute have attributed the scope to choose your plan – within a limited range of options – to two processes or ‘switches’ that turn parts of a genome on or off and exaggerate other parts. Methylation is an off switch while acetylation is the on switch. “We now have evidence that changes in methylation patterns occur in genetically identical people and therefore these changes can potentially change disease susceptibility,” reported the institute’s Dr Susan Clarke. 

The field of epigenetics is basically the science of manipulating mechanisms involved in switching certain genes on and off and methylation and acetylation are just two epigenetic factors. So what have you got and what can you control?

IQ and behaviour

The argument that one little wine won’t hurt loses its footing against Indiana University research finding that consuming alcohol during pregnancy changes embryos’ epigenetic marks, abnormally flicking switches in genes in offspring’s brains, potentially leading to low IQ and behavioural problems. Even mum’s lunchbox could have left its mark on your epigenome. In a US study, mice whose pregnant mothers ingested chemical bisphenol-A (BPA), which until recently was a staple of plastic water bottles and food containers, were more likley to be born yellow as a result of decreased methylation in a particular gene linked back to BPA. But this goes to show how fickle the whole gene game is: BPA-exposed mice whose mothers consumed methyl-rich foods came out predominantly brown, suggesting that flicking gene switches is all about levelling scores.

Memory and stress response

You mightn’t remember it, but your experience as a tot may have changed your brain’s epigenetic markers. McGill University neurobiologist Michael Meaney conducted a fascinating study of early experience on gene expression. Profiling newborn rats, Meaney’s team placed pups whose mothers didn’t lick them (the rat version of a mother’s touch) with surrogate parents who did lick, and found that the experience of being licked correlated with being more chilled out in adulthood. The licked rats exhibited major differences in the brain’s hippocampus – linked to organising memories and regulating response to stress hormones. Licking synced with inhibiting production of stress hormones by switching on certain genes. Hippocampus neurons in under-licked rats were less able to dampen animals’ stress response, leaving the under-licked rats chronically frazzled.

Cognitive decline

If you were the kid hiding out in the library after having your fairy bread stolen, the trauma may have left its mark on your DNA, according to a new study linking childhood bullying to genetic wear and tear and accelerated biological ageing. A study tracking 1,100 sets of twins from birth published in the journal Molecular Psychiatry showed that experiencing two types of violence-related stress in the second five years of life shrank DNA sequences called telomeres, involved in chronic disease and ageing. “Some of the billions of dollars spent on diseases of ageing such as diabetes, heart disease and dementia might be better invested in protecting children from harm,” said Duke University Institute for Genome Sciences & Policy researcher Idan Shalev in a news release. It backs previous findings that stress can accelerate telomere loss.

Addiction

Some of your genetic coding could hark back to when granddad was chewing tobacco during that two-up tournament. Recent research shows that epigenetic changes can survive more than one generation unchanged, inviting all sorts of ancestral finger pointing. A study from the Los Angeles Biomedical Research Institute published in BioMed Central Medicine suggests that exposing pregnant rats to nicotine not only predicted asthma in their offspring, but forecast the condition in the offspring’s offspring. The grandchild rats of nicotine-exposed grandparents exhibited similar airway constriction and elevated levels of nicotine receptor molecules as the offspring of nicotine-exposed mothers, researchers reported. Researcher Dr Virender Rehan theorised that epigenetic modification altered sex cells to program lungs to develop to express genes in the same abnormal ways as in first generation offspring.

Personality

If you think you got the bitch gene or blame DNA for your jumpy disposition, you mightn’t be too far wrong. Research in the fledgling field of behavioural genetics shows links between biology and personality. In her book Personality Theories: An Introduction, Barbara Engel says that heritability accounts for around 40 per cent of the five factors commonly thought to comprise personality: openness, conscientiousness, extraversion, agreeableness and neuroticism. Functional neuroimaging has further linked genetic mechanisms and anxiety-related personality traits, she writes. However, Engel says that even genetically coded behaviours aren’t impossible to change.

Sexuality

A controversial study published in The Quarterly Review of Biology argues that homosexuality is the result of sex-specific epi-marks bypassing an ‘erasure’ process and being passed from father to daughter or mother to son. Different epi-marks protect different sex-specific traits from being masculinised or feminised and are thought to affect sexual identity and partner preference.

Mental illness

Gene expression is implicated in myriad mental illnesses and mood disorders including borderline personality disorder, depression and schizophrenia. Take a study published in January in the journal Neuropsychopharmacology, which revealed certain alterations in gene expression thought to contribute to structural and functional brain changes associated with depression. In studies of animals, when chromatin (to do with chromosomes) structure was altered by epigenetic events, gene expression affected depression-related behavior, the effects of antidepressants and resistance to depression. Post-mortems have identified similar mechanisms in the brains of humans. According to psychiatrist Dr Bruce Kehr of Potomac Psychiatry, “there is no ‘depression gene’ or ‘anxiety’ gene. One inherits a susceptibility to these conditions through multiple different genes, but the genes alone do not cause the illnesses. The genetic material within the nucleus of brain cells must first be influenced by epigenetic factors that come from outside the brain, such as external environmental or internal physiologic factors.” Stressors such as a tiff with a colleague, or inflammation caused by alcohol or drugs, can tip predisposing genes over the edge, activating disorders such as anxiety disorder, depression and bipolar disorder and OCD, Dr Kehr says.

Eating behaviour

If you’re familiar with kilo creep or the diet cycle, you may have inherited genes that encourage you to overshoot your calorie needs according to leading endocrinologists. Associate professor Jerry Greenfield, from Sydney’s Garvan Institute, agreed with a study published in the New England Journal of Medicine showing a direct correlation between soft drink consumption, obesity and genetic predisposition to weight gain. “…people are consuming more calories because their genes are driving them to do so,” he said. “Genes not only drive people to eat more, they also predispose at-risk people to gain more weight with calorie overconsumption. It’s a double-whammy.”

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