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Abstract

The simplest of daily physical activity almost all people accomplish is walking. The advancement of technology has made it easier to track the number of daily steps with wearable devices. A study recently published in JAMA discovered that individuals taking 7000 steps or more per day lowered their risk of death.

Acetylcholine response

How Does Physical Activity Prevent Health Conditions & Mortality?

The health benefits reaped from regular physical activity, be it moderate- or vigorous-intensity, are many. From reducing the risk of heart diseases to promoting mental wellbeing, the list is long.

According to the CDC, almost a dozen of health conditions can be prevented or managed with routine physical activity:

According to some stats, about 6-10% of the health burden of chronic diseases worldwide and 9% of premature death can be attributed to physical inactivity. 

The 2019 Physical Activity Guidelines for Americans recommends adults to engage in weekly 150-300 minutes of moderate-intensity physical activity or 75-150 minutes of vigorous-intensity physical activity.

Image: Physical Activity Guidelines for Americans

Every individual has a different body type and consequently different bodily needs. Therefore, the realization of a personalized therapeutic approach has aided in the fitness world too. 

A strength-based approach uses healthcare professionals in close collaboration with clients - wherein the focus is put on clients’ abilities, objectives, and present situation.

Strength-based personal approaches to exercise regimes have been observed to bring about more excellent patient outcomes.

Xcode Life’s Gene Fitness Report analyzes your body’s genetic predisposition for fitness traits and gives personalized recommendations. Click here.

Physical Activity & Reduction in Mortality Risk: Previous Studies

A study in 2020 found a reduction in mortality risk by 40% when subjects followed the 2018 Physical Activity Guidelines for Americans and engaged in both aerobic and muscle-strengthening activities. Further, individuals who engaged in either aerobic or muscle-strengthening activities decreased their mortality risk by 29% and 11%, respectively.

According to data, between 1997-2014, only 15.9% of 479,856 Americans followed the recommended physical activity guidelines.

A 2015 study on European subjects showed a 14% reduction in mortality risk with only 15 minutes/day of exercise. 

Further, in a study done in 2020 on a group of 70-years olds, a higher step count was associated with a reduced incidence of diabetes.

The Study: Per Day 7000 Steps Or More Can Reduce Mortality Risk

The study led by Amanda Paluch was part of a Coronary Artery Risk Development in Young Adults (CARDIA) study which drafted subjects from four States - Alabama, Illinois, Minnesota, and California.

The study analyzed a subset of 2110 participants belonging to the age group of 38-50 years. Out of 2110, 1205 participants were women, and 888 were Black.

Study Conditions

The researchers grouped the participants into three categories:

  1. Low (<7000 steps per day)
  2. Moderate (7000 to <10,000 steps per day)
  3. High (>=10,000 steps per day)

Between 2005-2006 and a follow-up in 2015-2016, participants wore an accelerometer for seven days to measure average step count. The accelerometer was only allowed to be removed during sleep and any water-related activities.

At the end of the follow-up period of an average of 10.8 years, 72 participants had died. 

Additionally, the participants’ highest number of steps per minute in any 30 minutes was measured. The time duration each day in which the participants took 100 steps a minute was also tracked.

The researchers considered several other health-related factors like alcohol intake, weight & BMI (body mass index), smoking, cholesterol & fasting glucose levels, blood pressure, medication history & heart disease.

Findings of The Study

Compared to participants who took less than 7000 steps each day, participants who took at least 7000 steps each day reduced mortality risk by 50-70%.

Neither a step count exceeding 10,000 steps each day nor the step intensity had any additional impact on reducing mortality risk.

The study’s findings bear clinical significance as remote patient monitoring devices are gaining ground. Wearable devices to track daily step count is an easy way to track and promote routine physical activity. While many individuals may be reluctant to engage in planned-out exercise regimes, walking to accomplish step goals can be an acceptable form of daily activity.

Summary

  1. Routine physical activity has multiple health benefits, including reducing the risk of heart diseases and promoting mental wellbeing.
  2. A strength-based approach for physical activity depending on individual abilities and objectives has benefited more in the long run.
  3. Many studies have confirmed the reduction of mortality risk in light of routine physical activity.
  4. The study discovered that a minimum of 7000 steps each day could reduce mortality risk by 50-70%.

References

  1. https://doi.org/10.1001/jamanetworkopen.2021.24516
  2. https://www.cdc.gov/nccdphp/sgr/npai.htm
  3. https://www.cdc.gov/nccdphp/sgr/mm.htm
  4. https://www.bmj.com/content/370/bmj.m2031 
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6947527/

Abstract

The autoimmune regulator (AIRE) gene is crucial for distinguishing the body's cells from foreign cells. A recent study has found that the absence of the AIRE gene results in infertility problems in males. In addition, the study found that AIRE deficient infertile mice exhibited symptoms similar to an autoimmune disorder in men. The study further suggests that autoimmune diseases can impact fertility.

The AIRE Gene

The AIRE gene provides instructions for making a protein called an autoimmune regulator. This protein is primarily expressed in the thymus, an organ located near the breastbone. The crucial function of this protein is to protect the body's cells from foreign invaders. The malfunction of this protein leads to a condition called autoimmunity (inability of the immune system to distinguish body cells and foreign cells, resulting in self-injury). 

The AIRE Gene And Male Infertility

Male factors like ejaculation issues, inability to produce healthy sperm and dilated veins around the testicles have been estimated to contribute to infertility to a large extent. The absence of the AIRE gene is one of the determinant factors of infertility. A deficiency in this gene leads to the loss of proteins responsible for sperm production, resulting in infertility.

AIRE-dependent central tolerance is a process by which male fertility is protected by preventing autoimmune attacks on the reproductive targets.  An impaired AIRE- dependent central tolerance could lead to male infertility.

The Study: Impact of AIRE Deficiency on Male Infertility

Researchers began by mating AIRE deficient male mice and normal male mice with normal female mice.

The research study made the following observations in the AIRE deficient male mice

It was also found that AIRE deficient mice had low testosterone levels (male sex hormone), and that their immune system injured their reproductive organs, especially epididymis.

Researchers further made the following suggestions:

Summary

References

Abstract 

It is normal for hair to lose color and turn gray as people age. However, today’s stressful lifestyle can accelerate this process resulting in grey hair appearing on people even in their 20s! Initially thought as a permanent change, new research reveals hair greying can be reversed - at least temporarily!

How Does Hair Get Its Color

Hair greying occurs when melanin, a natural skin pigment that is responsible for hair, skin, and eye color, is gradually lost due to aging. At first, hair grows unpigmented out of the hair follicles. 

Two pigments, melanin (produced by melanocytes) and keratin (produced by keratinocytes), together add color to the hair. Both melanocytes and keratinocytes are present near the follicles.

Melanin has two different versions - eumelanin and pheomelanin. Eumelanin gives rise to a red/yellow pigment (seen in blonde/ginger hair), and pheomelanin gives rise to a brown/black pigment (seen in brunette/black hair).

Types of melanin

The distribution of eumelanin and pheomelanin is influenced by genetics, especially the MC1R gene

What Causes Grey Hair?

McSCs and Hair Greying

As our body ages, so do stem cells - the parent cells of all functional cells of the body. Melanocytes are produced by melanocyte stem cells (McSCs). 

Aging causes a loss of McSCs - so melanocyte production also gradually decreases. In the absence of melanin pigment, the hair turns grey. 

Hair greying is influenced by genetic factors and the environment (including lifestyle). One of the major environmental contributors happens to be stress. 

A previous study done by Harvard University explored stress-induced hair greying in mice. They observed that stress triggered the release of a chemical, norepinephrine, which affected the McSCs. 

Norepinephrine accelerated the conversion of McScs to melanocytes, thereby depleting the population of McScs. This ultimately resulted in a complete halt in the hair coloration process. 

This process was also noted to be irreversible in mice.

IRF4 - The Hair Greying Gene

In 2016, researchers at UCL, UK, found the first-ever gene, IRF4 (interferon regulatory factor 4), associated with hair greying. IRF4 is actively involved in the regulation of the production and storage of melanin. 

This gene interacts with MITF (microphthalmia-associated transcription factor) to activate tyrosine, a critical factor in melanogenesis (the process of melanin production). MITF has been known to repress McSCs survival and affect hair greying. 

So, researchers hypothesize that IRF4 might influence the hair greying process. However, the exact mechanism behind this is still unclear.

The Study: Stress-induced Hair Greying May Be Reversible!

Researchers at the Columbia University Irving Medical center undertook a small-scale study to observe how stress affected hair greying. The study included 14 participants from varying age groups, ethnicities, and sexes - most people, however, were white. The researchers collected dark, white, and two-colored hair (hair with partial greying) from these people.

The researchers used a digital and mathematical model to map and measure small color changes in a single hair. They found that over a stress-filled period, the hair started greying. 

Surprisingly, the removal of the stress stimulus resulted in an apparent reversal of greying, and the hair became colored again.

To understand the mechanism behind this, the researchers studied thousands of other proteins in the hair. They observed changes in 300 out of the 1000 proteins as the hair greyed.

They also suspect the role of mitochondria in stress-induced hair greying. Mitochondria, other than being involved in energy production, also plays an important role in transmitting signals that respond to psychological stress. 

Hair Greying Is Reversible - But Only in Some!

A 70-year old with a head full of white hair cannot reverse hair greying by reducing stress. At the same time, 10-year-olds, no matter how much stress they experience, are not going to suddenly wake up to a head full of white hair. 

The study reports a "threshold" or a limiting situation at which a hair turns grey permanently. Somewhere in middle age, as we approach this threshold, stress can accelerate the transition. 

Reducing stress in life is most definitely a good thing. But once you cross this threshold, it's not going to reverse your hair greying.

Let's Delay Hair Greying

  1. Exercising, meditation, and a balanced, healthy diet are few of the most effective ways to keep your stress at bay.
  2. Reducing sugar intake can help prolong the life of adult stem cells.
  3. Alcohol intake negatively impacts stem cell function. So keep drinking to a minimum.
  4. A lack of good sleep persistently can be very detrimental to stem cell function in the body. It is important to ensure 7-8 hour sleep cycles.

Summary

  1. Stress-induced hair greying occurs as a result of loss in melanin-producing cells.
  2. A study has reported that in some cases, when stress is removed, the changes associated with hair greying are reversed.
  3. A healthy lifestyle with good dietary habits, regular exercise, adequate sleep, and minimum stress can help prolong hair greying.

References

  1. https://doi.org/10.7554/eLife.67437 
  2. https://doi.org/10.1038/s41586-020-1935-3 
  3. https://doi.org/10.1038/ncomms10815 
  4. https://www.ncbi.nlm.nih.gov/pubmed/21054932

Abstract

When we are born, we inherit (receive) the genes from our parents, but we don't inherit their age. 

In other words, how do older parents give rise to young offspring?

Scientists have tried to explain this by a process called "natural rejuvenation event." This event sets our biological age to zero, which is the beginning of aging in mammals.

This event happens as the zygote develops to form an embryo. A zygote is a single-celled organism resulting from a fertilized egg. The zygote goes through a cellular multiplication process to give rise to the multi-celled embryo.

Embryonic rejuvenation event

Researchers are studying the possible application of this "age reversal event" as a therapeutic intervention for age-related diseases, such as arthritis or Parkinson’s.

What is Aging?

Aging is something we all experience but actually know very little about. Hair greying, wrinkles formation, joint changes, etc., are signs of aging. Aging, on the other hand, encompasses all the processes that occur in the body that result in these signs - it is a combination of physiological changes in our bodies and environmental factors. 

Aging eventually leads to physical denaturation, dysfunction, and ultimately mortality (death).

As we age, every cell in our body gets old due to the progressive accumulation of damage through the intervening years. But this cellular damage does not get passed on to human offspring to the next generation – the absence of this cellular damage in human offspring has baffled scientists for generations. 

That's because germline cells (sex cells - egg and sperm that form the embryo/zygote) rejuvenate in the offspring after conception.

Rejuvenation Event In The Embryo

During the initial stages of embryogenesis (the formation of the embryo), life hits a reset button — the rejuvenation event in the embryo. When an embryo is attached to the uterus, the rejuvenation event sets the developing embryo to grow at its youngest biological age – zero. This rejuvenation of the embryo marks the beginning of the mammalian age.

The epigenetic aging clock is a biochemical test used to measure age. It was developed with conserved cytosines - units in DNA whose methylation levels change with age. Experts use these epigenetic clocks to predict the approximate ages of mouse embryos at their early stages of development.

They found that the age of mouse embryos stayed constant for the first few days after fertilization. However, by around 6.5 to 7.5 days into development, the biological age of the embryos witnessed a dip, indicating that they are undergoing some type of rejuvenation event. 

The researchers say that the biological age of mice is set to zero, somewhere between 4.5 to 10.5 days after fertilization.

Eventually, during development, the biological age begins to slowly rise. However, the point exactly at which this growth happens is still unclear.

Rejuvenation event in mouse embryos

At present, similar data for humans is unavailable as studying human embryos at such early stages is prohibited. Recent studies have shown that the epigenetic clocks in cord blood can be used to estimate gestational age at birth.

Potential Applications

When embryos can reset the biological clock, there is a hope to reverse the errors that occur due to cell damage, restoring the cells back to their agile state, eliminating signs of aging.

This hypothesis could possibly help researchers develop treatments for age-related diseases, such as arthritis or Parkinson’s - A paradigm shift in treating age-related illnesses.

Video

Summary

  1. The mystery behind how aged parents produce youthful offspring has puzzled researchers for a long time now.
  2. A recent study revealed a natural rejuvenation event during early embryogenesis that sets our biological age zero.
  3. The study noted that mouse embryos experience the rejuvenation event around 4.5 to 10.5 days after fertilization.
  4. Epigenetic aging clocks can help predict the embryos' biological age and the onset of aging in mammals.
  5. This approach may pave the way for researchers to find treatment for age-related diseases by reversing the errors due to cell damage (using the same concept of age reversal seen in embryos).

References

Abstract

Vitamin D deficiency is a common health problem worldwide among all age groups. Previous research studies have reported that ultraviolet (UV) exposure causes the skin to produce the hormone endorphin, which is chemically related to morphine, heroin, and other opioids.

A subsequent study reported that UV exposure raises endorphin levels in mice, displaying behavior consistent with opioid addiction. Recent research suggests that vitamin D supplementation may play a role in fighting opioid addiction.

What Is Vitamin D Deficiency?

Vitamin D, essential for a range of bodily functions, is predominantly obtained from exposure to sunlight. Once the body takes up vitamin D, it needs to be converted into its active form. Vitamin D is also naturally present in dietary sources like fish liver oils, fortified grains, dairy products, and egg yolks. 

Vitamin D deficiency can occur when a person’s skin has an impaired ability to synthesize vitamin D from the sun. Individuals can also become deficient when their bodies cannot absorb the vitamin or convert it to its active form. People who avoid sun exposure, adhere to a vegan diet, or suffer from milk allergies may also be at a higher risk of vitamin D deficiency. 

Vitamin D is vital for strong bones as it helps the body use calcium from the diet. Vitamin D deficiency has been associated with rickets, a condition leading to soft bones and skeletal deformities. However, increasing research suggests the importance of vitamin D in protecting against other health problems.

Know more: Genetic Factors That Could Increase Your Risk For Vitamin D Deficiency

Opioids Addiction: Tolerance

Opioids are a form of narcotic prescribed as an over-the-counter pain medication. If incorrectly used, they can have serious side effects and even result in opioid addiction.

Individuals may gain tolerance to opioid medication if taken regularly and might need an increased dose to achieve the same effect in easing pain. They may also develop a dependence on the medication due to extended period use. In this case, individuals who abruptly stop the drug use may experience withdrawal symptoms.

How Does Vitamin D Deficiency Influence Opioid Addiction?

A study led by Dr. David Fisher and his team of researchers at the Massachusetts General Hospital examined the potential link between UV radiation, vitamin D, and opioids.

Initially, the researchers began by studying two data sets. 

  1. The National Health and Nutrition Examination Survey with roughly 20,000 participants 
  2. Data of 3,000 Massachusetts General Hospital (MGH) patients between 2014 and 2016 with opioid use and more than 8,000 matched controls.

The researchers drew the following conclusions from the data sets:

These results accounted for factors like age, gender, history of bone fractures, and chronic pain. However, further investigation was required to understand the association between low vitamin D and opioid use.

The Link Between Opioid Addiction And Vitamin D 

The researchers used mouse models to understand the patterns seen in the clinical data. 

They induced vitamin D deficiency in the mice using the following methods:

50% of the diet-deficient mice were put on a regular diet for eight weeks before examining their response to morphine.

All the mice were then subject to a conditioned place preference (CCP) test in which the mice are placed in a multi-compartment chamber, trained to anticipate morphine in one chamber. Researchers then measured how long the mice spent inside the morphine chamber.

The following were observed:

The team found that the effect was reversed when they restored vitamin D levels using supplements. The researchers confirmed the results with a new batch of mice and additional sensory cues. 

Furthermore, the researchers wanted to know whether vitamin D deficiency influenced how mice respond to opioids. For this, they placed control and deficient mice on a hot plate and measured their response to physical pain. Then, the test was rerun after administering the mice with morphine. 

Test results reported that vitamin D–deficient mice stayed on the plate longer, implying the morphine worked more effectively as a pain reliever. There was an effect reversal upon vitamin D restoration. Additionally, the heightened pain threshold from a lack of vitamin D disappeared, demonstrating that the effect is opioid-mediated. 

Are You Meeting Your Vitamin D Needs? Find out with our Gene Nutrition Report!

Vitamin D Deficiency and Ultraviolet (UV) Radiation exposure

The researchers exposed transgenic mice lacking vitamin D receptors to UV. Similar to earlier results, daily exposure to low-dose UV increased pain tolerance in the vitamin D–deficient mice. Findings also show that the mice spent more time in compartments associated with UV exposure, suggesting a lack of vitamin D sensitizes them to the rewarding effects of UV.

The team believes that mice and humans may have evolved molecular pathways to benefit from UV and vitamin D. These pathways induce the same feelings one might get when taking opioids but then control the cravings once vitamin D levels are sufficient.

Previous studies suggest that some people develop an urge to sunbathe and tan, mirroring the behaviors of opioid addicts. Fisher and his colleagues hypothesized that people seek out UV to benefit from an endorphin rush. 

In conclusion, vitamin D deficient people would feel compelled to seek out the sun, receiving an endorphin rush. But once their bodies generate enough vitamin D, the endorphin production stops. In the case of opioids, there is no molecular switch to turn off the craving. 

The association between vitamin D and opioid response can help with patient care. Checking vitamin D levels before a patient’s surgery could determine whether they are likely to have a heightened tolerance or develop an addiction. 

Recommendations For Healthy Vitamin D Levels

Also read: Will Fish Oil Supplements Help Your Heart Health? Depends On Your Genetic Makeup!

Summary

Video

References

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4018438/

https://www.the-scientist.com/news-opinion/vitamin-d-deficiency-drives-opioid-addiction-in-mice-68897

https://advances.sciencemag.org/content/7/24/eabe4577.abstract

https://www.sciencedaily.com/releases/2021/06/210611174042.htm

Fish oil is one of the most commonly used dietary supplements. It is rich in omega-3 fatty acids. It has been known to protect against heart diseases, lower blood pressure, and lower triglyceride levels.

According to a recent study published in the journal PLOS Genetics, the beneficial effect of fish oil on triglycerides is seen only in people with a certain type of genetic makeup.

What are Triglycerides?

Triglycerides (TG) are the most common type of fats present in your body. TG are commonly found in foods like butter, margarines, and oils. The extra calories that the body doesn’t need to use right away are also stored as triglycerides.

High triglyceride levels are considered to be a marker (indicator) for heart diseases. A blood sample reading of less than 150 milligrams per deciliter (mg/dL) is considered to be the normal level of TG. Higher levels of triglycerides may thicken the walls of the arteries, thereby increasing the risk of stroke and heart diseases.

Fish Oil

Fish oil is a rich source of omega-3 fatty acids, a type of polyunsaturated fatty acids (PUFA), which is very important for your heart health. Fish oil can be derived from consuming oily fish like mackerel and salmon or through supplements. Some fish oil products are approved by the US Food and Drug Administration (FDA) as prescription medications to lower triglycerides levels.

But, a recent study published in the journal PLOS Genetics claims that “taking fish oil only provides health benefits if you have the right genetic makeup.”

The Study

The study focussed on the effects of fish oil on triglyceride levels in the blood. The study also examined the levels of the other three blood lipids - high-density lipoprotein, low-density lipoprotein, and total cholesterol. All these types of fats (lipids) are biomarkers for heart diseases.

The study analyzed the data of 70,000 individuals taken from UK Biobank. The study cohort was divided into two - those who took fish oil supplements (around 11,000) and those who didn’t.

After running over 64 million tests, it was found that people on fish supplements who experienced a reduction in their triglyceride levels had a specific genotype of the GJB2 gene.

Individuals with the AG genotype who took fish oil decreased their triglycerides.

The study further revealed that individuals with the AA genotype who took fish oil had slightly elevated levels of triglycerides. The effects of fish oil on triglycerides in people with GG type could not be determined as present in the variant rs112803755. So, if you have your DNA raw data file with you, you can look up this rsID to find out your genotype!

Learn How To Use Xcode Life’s Gene Tool To Look Up Your Genotype here!

Recommendations to Reduce Your Triglyceride Levels

Apart from fish oil, there are also other effective methods to reduce your triglyceride levels. Some of them include:

Limiting your sugar intake

Excess sugar in your diet is turned into triglycerides, elevated levels of which are not good for your heart health. According to a study, replacing your sugary beverages with water can decrease your triglyceride levels by as much as 29 mg/dL.

Adopting a low-carb diet

The extra carbs in your diet are also converted into and stored as triglycerides. Following a low-carb diet has proven to be much more effective than following a low-fat diet in terms of reducing triglyceride levels.

Exercising regularly

HDL cholesterol is a type of good cholesterol. Increasing HDL levels can both help reduce triglyceride levels as well as counteract the effects of high triglycerides. Jogging for even two hours per week can reduce the levels of triglycerides.

Limiting Alcohol Intake

Alcohol is high in sugar and calories. If they are not used up by the body, they are converted into triglycerides. According to studies, even moderate alcohol consumption can increase your triglyceride levels by as much as 53%. This applies to people with normal triglyceride levels as well!

Summary

  1. High triglyceride levels are a marker for many heart diseases, as they contribute to plaque build-up in the arteries.
  2. Fish oil is one of the commonly used supplements and is rich in omega-3 fatty acids. It has been known to reduce triglyceride levels.
  3. According to a study, the effect of fish oil on triglyceride levels was found to be beneficial only in people with a specific genetic makeup.
  4. Upon analyzing the data of 70,000 people, the study found that fish oil reduces triglyceride levels only in people with the AG genotype of the GJB gene.
    Do You Carry The Beneficial AG Genotype? Find Out Using Xcode Life’s Gene Tool!
  5. Further, people with the AA genotype experienced a slight increase in triglyceride levels upon fish oil consumption.
  6. Some other effective ways of reducing triglyceride levels are regular exercising, lowering the consumption of high-sugar and high-carb foods, and limiting alcohol intake.

Use Xcode Life’s Gene Tool to find out your genetic marker for lowering triglyceride levels with fish oil supplements

References:

  1. Should you take fish oil? Depends on your genotype
  2. GJB2 gene
  3. Substituting water for sugar-sweetened beverages reduces circulating triglycerides
  4. A low-carbohydrate as compared with a low-fat diet in severe obesity
  5. Effects of long-term, self-monitored exercise on the serum lipoprotein and apolipoprotein profile in middle-aged men
  6. Effect of moderate alcohol consumption on hypertriglyceridemia

Identical twins, also known as monozygotic twins, are believed to have identical sets of genes since they are formed from the same fertilized egg. 

Studies on identical twins have been used as a key research tool to tease apart the genetic and environmental contributions to a disease. For example, in the case of identical twins raised apart, if one has diabetes and the other doesn’t, blaming the environmental/lifestyle factors has been the classic approach - owing to their identical genetic material.

However, recent research suggests that this is not entirely true. Even twins developed from the same fertilized egg can have minor differences in their genomes - and these changes can happen during the first week of fetal development. 

The Study

According to a new study published in Nature, the genomes of identical twins can have small genetic differences which may impact their lives significantly. This study was performed by a group at deCODE genetics, an Icelandic biopharmaceutical company. 

The study involved 380 pairs of identical twins, two pairs of triplets, and their closely related families. Next-generation sequencing (NGS) technology was employed to sequence their genomes. NGS is the gold standard of sequencing in recent times that provides the test results within a day.

The results of this study show that, on average, 5.2 mutations differ between the pair of twins, and these differences occur in the early stages of growth.

Despite developing from the same fertilized cell, how do these mutations occur?

To understand that, let’s go over some terms:

Hereditary mutations occur in the gametes (organism’s reproductive cells - the sperm or egg cells). These are passed on from parents to their offspring.

When the sperm and eggs fuse to form the zygote (fertilized egg), these mutations are passed on to each cell of the resulting embryo. Since identical twins are formed from the same fused zygote, in theory, it only makes sense that they carry the same mutations.  

Somatic mutations occur only when the zygote starts to grow - during the first week of zygote development. They commonly occur as a result of errors in the cell division process.

In the case of identical twins, the zygote splits into two during the first week of development. 

While the hereditary mutations are split equally, the somatic mutations may be divided unequally in some cases. This random distribution of the somatic mutations can bring about certain differences between the twins. 

Coming back to the study, in 15% of the twin pairs studied, one twin had significantly more developmental mutations than the other. 

These differences, though very minor, can contribute to significant differences in health outcomes. In fact, they are enough to predispose one twin to developmental disorders like neonatal cancer and keep the other one healthy! 

Summary

  1. Scientists thus far have been conducting twin studies with the belief that they have identical genetic makeup, and thus, any differences in them can only be attributed to environment/lifestyle.
  2. A new study has come to light that challenges this theory. The study identified an average of 5.2 mutations difference between the pair of twins. 
  3. While hereditary mutations occurring in sperms and eggs are passed on equally between the twins, it’s not the case for somatic mutations. They develop during the first week of zygote development as a result of errors in cell division. These mutations are randomly distributed between the split zygote cells.
  4. The minor differences in the mutation distribution has the potential to have significant health impacts. In fact, they could increase the risk of conditions like neonatal cancer on one twin while keeping the other one healthy.

Reference 

  1. https://www.businessinsider.in/science/news/identical-twins-dont-always-have-identical-genes-research-shows-a-new-twist-in-the-nature-versus-nurture-debate/articleshow/80157404.cms
  2. https://www.nature.com/articles/s41588-020-00755-1
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