The Legacy of George the Tortoise

George the beloved tortoise died at age 100 and was the last of his kind. He was a Pinta tortoise that will be missed by animal lovers. Luckily geneticists have been able to publish his genome to study longevity, immunity, and cancer resistance in humans.

To properly analyze the DNA, researchers sequenced the DNA of another species of tortoises, the Aldabrachelys gigantea for comparison. The study found that the same genes for longevity in humans are the same for tortoises and that throughout the years environmental factors favored genes associated with longer lives. Also these reptiles had duplicated immune system genes, tumor suppressing genes, and genes for DNA repairs. Overall, multiple genes are responsible for longevity.

Tortoise populations has been in decline prior to human encroachment. The effects of living on a geographically isolated island such as the Galapagos Island, have limited the gene pool and decreased genetic diversity. Also the tortoise is known as a k reproductive strategist meaning less fecundity and longer maternal care for the offspring. Very few factors including longevity were in their favor. But humans exacerbated their decline in the 1800s through “tortoise harvesting”- they make a nice snack! Our exploitation of their meat of an already vulnerable population led to their drastic decline and extinction.

Everywhere the human population goes, we wreak havoc on native species. But rather than accept our destructive nature, we are learning from it through science. And the timing is too perfect. I recently read an article reporting that the US life expectancy has dropped to 78.6. Finding a way to increase longevity is especially imperative nowadays. If we can study tortoise DNA from all over the world and can obtain an extensive and holistic database of it, then maybe we can address this problem.

Links:
https://www.smithsonianmag.com/smart-news/lonesome-george-giant-tortoise-reveals-cancer-fighting-and-longevity-genes-180970948/
https://www.nature.com/articles/s41559-018-0733-x 

https://www.cdc.gov/nchs/data/databriefs/db293.pdf

 

Your Lifelong Partner Can Determine How Long You Live

The debate of nature vs nurture has been raging on for decades without a clear agreement on which factor has greater influence on areas such as mental health, development, etc. The particular article I read dealt with the association of life expectancy to our genes and lifestyle. Prior studies conducted have indicated that genetics plays a significant role in human life expectancy, an upward to about a 30% influence when comparing the life span between close relatives. This article reflects on a paper that contradicts such high influence, by questioning the breadth of previous research. Newly published research indicates that environment has a more of an effect on longevity than previously thought, with spouse partnering being of significant influence.

In the study, researchers drew data from millions of family trees provided by the company Ancestry, and analyzed the degrees of influence of several factors, such as family, environment, socioeconomic status, marriage and in-law relationships. What they found unique was that there was a stronger correlation in life expectancy between spouses than that of siblings, which they attributed to "assortative mating." Assortative mating is explained to be a trend where people seek partners who share traits similar to theirs (like attracts like). Therefore, through similar living conditions and similar traits (be it physical or socioeconomic), spouses shared a very similar life span. This finding, the researchers note, reduces the influence of genetics on life span explaining that previous studies tend to leave this factor out of their studies, which "inflated the suspected influence of genetics alone"(Ruby et al. 2018). 

I think the findings and implications of this research highlights the complexity in studying genetics. Whether its discerning the chemical substance responsible for genetic inheritance, which took the need of several groundbreaking experiments before DNA was confirmed as such material, or discerning the level of influence genetics has on life expectancy, each experiment has to be looked at with care and account for multiple variables. Indications and correlations can't be heavily established and followed as certainty after just one experiment, because there are more variables than one can ever account for in research. Therefore, new findings should always be taken with a grain of salt and continued to be built upon by further inquiry in order to establish a firmer relationship.

Link to published article (also embedded in text)

Common Gene Mutation linked to Longer Life in Males

An article in the New York Times discusses a gene described in the journal, Science Advances.  This gene has been found to increase the lifespan of males by ten years; the gene was found to have no effect on women.  Heredity is not the only factor that determines how long a person lives; in Germany the life expectancy in 1875 was 39 years, today the life expectancy is around 80 years.  The almost 50 year difference is a result of access to clean water, modern medicine, and other measures rather than evolution.  Although there are many outside factors, research has shown heredity definitely plays a large role in lifespan determination.  Many studies have shown identical twins have a much closer lifespan than fraternal twins due to the fact that they share the same genes.  Research on this topic has been rather disappointing to scientists; however, they did find a connection between the size of an animal and their lifespan.  Research has shown that smaller animals typically live longer than large animals.  These developments have lead researchers to look more closely at the molecules that causes our bodies to grow; specifically our growth hormones.  Researchers have found that about 1/4 of people have a mutation in the gene for growth hormone receptors which causes them to have a missing chunk of DNA.  Dr. Barzilai conducted a study using 567 Ashkenazi Jews and their children.  Dr. Barzilai found that 12% of men over the age of 100 possessed the growth hormone mutation which is about three times higher than the percentage of males over the age of 70.  For women in the study the gene was equally present in both age groups.  Researchers believe they have been able to establish a connection between longer-life and the growth hormones but need more research and a larger group to make a real connection.  A 2008 study showed a mutation in a different growth gene which only effected women; this shows that men and woman take a different genetic path toward longer lifespans.  Dr. Barzilai and many other scientists are still researching these genetic mutations and believe an answer is not far away.

Predicting Death

Methyl labels are key to determining whether a gene is being deactivated or read. Observing methylation at specific placements in the genome, scientist found links with cancer and other diseases. Only in certain combinations of DNA called CpGs, can you find methyl groups. Scientists analyze 500,000 levels of methylation to determine if there was a link to survival. They found that there was a connection between methylation and mortality in 58 of the CpGs. Smoking has the biggest effect on methylation and increasing mortality rate. DNA methylation seems to be reversible, so if a person quits smoking their mortality rate will decrease at a high rate.


Overall, DNA methylation seemed to relate most to survival. I think it's kind of a cool concept. It almost seems like if scientists can figure out how to increase methylation or keep it from ever decreasing, maybe life expectancies will continue to grow.

https://www.sciencedaily.com/releases/2017/03/170320104008.htm
http://www.nature.com/articles/ncomms14617

Life Expectancy in U.S. Declines Slightly

It’s recently been discovered that the life expectancy  for Americans has declined. This is actually the first time this has happened since H.I.V. related deaths were at an all time high in 1993. The increase in the death rate was over 86,000. The main issue with this happening is that researchers aren't able to find a single cause for this occurrence. The possible causes range from heart disease to suicides. Dr. Peter Muennig, a professor of health policy and management at Colombia University’s Mailman School of Public Health stated that, “A .01 decrease is huge. Life expectancy increases, and that's very consistent and predictable, so to see it decrease, that's very alarming.” Dr. Muennig believes that the reason for the decline in life expectancy can be pointed at the increase in both obesity rates and opioids. There is also a connection between the decline and race. The life expectancy for working class white people has dropped which could be because of alcohol abuse, suicide and economic issues. Income also has an effect because of the stress put on from financial troubles. The life expectancy for women continues to be higher than men by 4.9 years which has actually increased since 2014. The recent changes won’t pose a threat unless this decline continues to keep happening.

What's the Longest Humans Can Live?

Jeanne Calment set the record for the longest living person after she died on August 4, 1997 at 122 years old. Humans have been progressively living for longer over the last few centuries, but it is likely that we have reached our limit, at about 115 years, according to Dr. Jan Vijg from Albert Einstein College of Medicine. Other experts agree with him, but some disagree strongly, basing their arguments on the fact that life expectancies have been increasing rapidly since the early 1900s. However, studies have been done which look at the growth of the population of a given age from year to year. For example, in France in the 1920s, 85 year olds were the fastest growing group of people. This trend shifted to even older people as the average life expectancy grew but about a decade ago, the peak stopped shifting. This is likely due to the stall in life expectancy. The International Database on Longevity also points to the same conclusion- people are not living as long as they used to decades ago, and besides the rare case like Jeanne Calment's, no one is living longer than about 115 years.

It is predicted that 115 will be the highest age that anyone reaches in the foreseeable future. It has been an ongoing argument for years whether or not there is a limit to lifespans, and because people have been steadily reaching the same age for decades now, it seems that there are only so many years that a body can live and work and continue repairing itself before it collapses.
I agree that there is a certain ceiling for age that humans can reach. The body is simply not able to continue repairing itself after a certain point. Because of the advancements in medicine and quality of life that have been improving over the past few centuries, life span has been increasing steadily, but at this point in time we have most likely reached the limit to how old we can get. 

Gene Variants that could Shorten Lifespans

Researchers from the University of Edinburgh in the UK have identified two gene variants that can take up to 3 years off an individuals life. Working out everyday and eating healthy may not always guarantee a longer expected lifespan due to an individuals predetermined genome.The identified gene variants occur on genes referred to as APOE and CHRNA3/5. These gene variants are carried, at least independently, by more than 2/3 of the global population. However, only 3 out of every 1000 individuals carry both gene variants within their genomes.The presence of both these gene variants was seen in the genomes of individuals who died earlier than their calculated life expectancy.

 Although these genes have correlating effects, they are found on very separate parts of the individuals genome. 

The reasons why these genes have these effects are not yet clear, however, both genes have been linked to differing medical conditions known to shorten lifespans. CHRNA3/5 has been linked to a higher predisposition for lung cancer and severe respiratory problems. APOE has been linked with high risk of Alzheimer's disease, heart disease, and high cholesterol. All of these medical ailments alone can cause a lifespan to be shortened, so when combined the effects are more severe. The APOE variant effects more women then men, while CHRNA3/5 effects more men then women. However, when seen together these genes can effect the individuals life regardless of sex. Contrary to the appearance of this article how long you live is not solely dependent on your predetermined genetics. Lifestyle factors like environment also play a role in lifespan. The role of genetics in an individuals lifespan is very complicated, and much is still unknown. I am interested to see if the discovery of these gene variants leads to the discovery of other lifespan gene effectors. Or if more research on the determining factors of a lifetime are performed. 

Could Iceland's High Life Expectancy Be Caused By Good Genetics?

World Life Expectancies (Iceland 83.1)

Iceland has one of the worlds toughest climates to live in. Despite this, the people there live longer than just about every other place on Earth. The reason? Good genetics. The people who live the longest usually have a family history of longer lives. Kari Stefansson investgated this phenomenon by collecting genetics information on about 1/3 of Iceland's population. He and his company, DeCode Genetics then compared the genetic information from those 90 and up. What they found is that these people were more related to each other than the control groups. What they think happened is the harsh life of Iceland in the past, (unheated homes, agricultural hardship, and widespread poverty) made it difficult to survive. Those that did survive then passed on those hardy genes down to the next generation. Adding to this that people who die young in Iceland stilll drink the same water and breathe the same air, so there must be another cause, and Stefansson thinks it is in the genetics.

This article stood out to me because it shows how good genes passed on through generations can begin to add up. The articles make note that the good genetics probably started with the vikings. In the articles there is an interactive world expectancy map, and what I found interesting from scrolling over a couple of countries is the only other country with 83 years as the expectancy is Japan, another island nation. So, maybe not so much now, but in years past these could have been isolated populations where there wasn't as much genetic variation allowing the good genes to accumulate over time.

Is Y chromosome responsible for shorter life expectancy and higher cancer risk in men?

 

Overall, it is pretty well known that men have a shorter life expectancy, as well as a higher risk for certain types of cancers than women. An international group of researchers analyzed DNA samples from over 1,600 elderly men. They found that the loss of the Y chromosome in some white blood cells was the most common genetic alteration. They also found a correlation between the loss of the Y chromosome and a shorter life span, as well as an increased risk of cancer mortality. Everyone knows that the Y chromosome is mostly known because it is only present in men, and it plays a role in sex determination and sperm production. However, these researchers found that the Y chromosome also has a role in tumor suppression, which could explain why men get cancer more than women.

Hopefully in the future, the Y chromosome could predict the risk for men to develop cancer. Also, this new research could help determine why men have a higher risk for certain cancers opposed to women.

 

 

Article: http://www.sciencedaily.com/releases/2014/04/140428121205.htm

Related Article: http://www.biomedcentral.com/1471-2164/14/323