Yet another beneficial mutation in humans uncovered

[rogue06]

It appears that the people who live in the Quebrada Camarones region of Chile’s Atacama desert have evolved a mutation that allows them to drink the water with high levels of arsenic (over 100 times the World Health Organization’s safe limit) in it without ill effect.

Source: Human adaptation to arsenic in Andean populations of the Atacama Desert

Abstract

Objectives
Quebrada Camarones, in the Atacama Desert, has the highest arsenic levels in the Americas (>1,000 µg/L). However, the Camarones people have subsisted in this adverse environment during the last 7,000 years and have not presented any epidemiological emergencies. Therefore, to solve this conundrum we compared the frequencies of four protective genetic variants of the AS3MT gene associated with efficient arsenic metabolization, between the living populations of Camarones and two other populations historically exposed to lower levels of arsenic.


Materials and Methods
The Chilean selected population samples come from Quebrada Camarones (n = 50) and the Azapa Valley (n = 47) in the north and San Juan de la Costa (n = 45) in southern Chile. The genotyping was conducted using PCR-RFLP. We compared the genotypic and allelic frequencies, and estimated the haplotype frequencies in the AS3MT gene.


Results
We found higher frequencies of the protective variants in those people from Camarones than in the other two populations. The haplotype estimation showed that the combination of protective variants of CTTA is very frequent in Camarones (68%) and Azapa (48%), but extremely low in San Juan de la Costa (8%). Also, the C variant associated with toxicity risks in the SNP Met287Thr had a lower frequency in Camarones (1%) and is higher in the other populations.

Discussion
The higher frequency of protective variants in both northern Chilean populations indicates a long exposure to naturally arsenic-contaminated water sources. Our data suggest that a high arsenic metabolization capacity has been selected as an adaptive mechanism in these populations in order to survive in an arsenic-laden environment.



Source

© Copyright Original Source

As an article in New Scientist explains:

The body uses an enzyme called AS3MT to incorporate arsenic in two compounds, monomethylarsonic (MMA) acid and dimethylarsinic (DMA) acid. People who metabolise arsenic more efficiently convert more of it into the less toxic, more easily expelled DMA.

Mario Apata of the University of Chile in Santiago and his colleagues looked at variations in the gene coding for AS3MT in nearly 150 people from three regions of the country. They found higher frequencies of the protective variants in people from Camarones: 68 per cent there had them, as opposed to just 48 and 8 per cent of people in the other two. “Our data suggest that a high arsenic metabolization capacity has been selected as an adaptive mechanism in these populations in order to survive in an arsenic-laden environment,” the researchers conclude (American Journal of Physical Anthropology, doi.org/bz4s).

The variants that protect the Camarones people are called single nucleotide polymorphisms – changes in a single DNA letter of the genetic code. Anthropologist Lorena Madrigal of the University of South Florida in Tampa says these are such tiny mutations that they aren’t telling us exactly how the changes affect the enzyme molecule and its detoxifying effects.

Previous studies found similar mutations in the AS3MT gene that contribute to improved arsenic metabolisation in Vietnam and Argentina. Sequencing the entire chromosomal region around this gene could reveal more, but there’s still a long way to go before we fully understand the molecular mechanism for how arsenic resistance works.

Though it’s a fascinating example of what appears to be contemporary evolution in humans, it also underscores the water quality problems that many populations face, says Madrigal. And many may not be able to evolve to deal with it.

[Bisto]

So I must take my own water if I ever go there. Got it

[rogue06]

So I must take my own water if I ever go there. Got it

Considering the scarcity of water there (it's the world's driest desert where parts of it haven't seen a drop of rain since recordkeeping began) that would be advisable even if the water didn't have such high levels of arsenic.

[Sparko]

It appears that the people who live in the Quebrada Camarones region of Chile’s Atacama desert have evolved a mutation that allows them to drink the water with high levels of arsenic (over 100 times the World Health Organization’s safe limit) in it without ill effect.

Source: Human adaptation to arsenic in Andean populations of the Atacama Desert

Abstract

Objectives
Quebrada Camarones, in the Atacama Desert, has the highest arsenic levels in the Americas (>1,000 µg/L). However, the Camarones people have subsisted in this adverse environment during the last 7,000 years and have not presented any epidemiological emergencies. Therefore, to solve this conundrum we compared the frequencies of four protective genetic variants of the AS3MT gene associated with efficient arsenic metabolization, between the living populations of Camarones and two other populations historically exposed to lower levels of arsenic.


Materials and Methods
The Chilean selected population samples come from Quebrada Camarones (n = 50) and the Azapa Valley (n = 47) in the north and San Juan de la Costa (n = 45) in southern Chile. The genotyping was conducted using PCR-RFLP. We compared the genotypic and allelic frequencies, and estimated the haplotype frequencies in the AS3MT gene.


Results
We found higher frequencies of the protective variants in those people from Camarones than in the other two populations. The haplotype estimation showed that the combination of protective variants of CTTA is very frequent in Camarones (68%) and Azapa (48%), but extremely low in San Juan de la Costa (8%). Also, the C variant associated with toxicity risks in the SNP Met287Thr had a lower frequency in Camarones (1%) and is higher in the other populations.

Discussion
The higher frequency of protective variants in both northern Chilean populations indicates a long exposure to naturally arsenic-contaminated water sources. Our data suggest that a high arsenic metabolization capacity has been selected as an adaptive mechanism in these populations in order to survive in an arsenic-laden environment.



Source

© Copyright Original Source

As an article in New Scientist explains:

The body uses an enzyme called AS3MT to incorporate arsenic in two compounds, monomethylarsonic (MMA) acid and dimethylarsinic (DMA) acid. People who metabolise arsenic more efficiently convert more of it into the less toxic, more easily expelled DMA.

Mario Apata of the University of Chile in Santiago and his colleagues looked at variations in the gene coding for AS3MT in nearly 150 people from three regions of the country. They found higher frequencies of the protective variants in people from Camarones: 68 per cent there had them, as opposed to just 48 and 8 per cent of people in the other two. “Our data suggest that a high arsenic metabolization capacity has been selected as an adaptive mechanism in these populations in order to survive in an arsenic-laden environment,” the researchers conclude (American Journal of Physical Anthropology, doi.org/bz4s).

The variants that protect the Camarones people are called single nucleotide polymorphisms – changes in a single DNA letter of the genetic code. Anthropologist Lorena Madrigal of the University of South Florida in Tampa says these are such tiny mutations that they aren’t telling us exactly how the changes affect the enzyme molecule and its detoxifying effects.

Previous studies found similar mutations in the AS3MT gene that contribute to improved arsenic metabolisation in Vietnam and Argentina. Sequencing the entire chromosomal region around this gene could reveal more, but there’s still a long way to go before we fully understand the molecular mechanism for how arsenic resistance works.

Though it’s a fascinating example of what appears to be contemporary evolution in humans, it also underscores the water quality problems that many populations face, says Madrigal. And many may not be able to evolve to deal with it.

Is it evolution or selective breeding? is it really a mutation to something new, or a natural variation that just got concentrated in this population because anyone without it dies?

[rogue06]

Is it evolution or selective breeding? is it really a mutation to something new, or a natural variation that just got concentrated in this population because anyone without it dies?

It is a mutation that is being selected for due to environmental pressure.

[TheLurch]

It is a mutation that is being selected for due to environmental pressure.

Which, to be clear, is evolution.

[Bisto]

Is it evolution or selective breeding? is it really a mutation to something new, or a natural variation that just got concentrated in this population because anyone without it dies?

It is a mutation that is being selected for due to environmental pressure.

Which, to be clear, is evolution.

I get the distinct impression that the three of you just said the same thing in different ways.

[rogue06]

I get the distinct impression that the three of you just said the same thing in different ways.

It is evolution if it is a trait that is passed on to offspring -- which it is.

[Sparko]

It is a mutation that is being selected for due to environmental pressure.

why is it a mutation and not a natural variation. If a group starts killing off everyone who is not blond, eventually all the nonblonde genes will be bred out and the population will all breed blonde.

[rogue06]

why is it a mutation and not a natural variation. If a group starts killing off everyone who is not blond, eventually all the nonblonde genes will be bred out and the population will all breed blonde.

Because as the OP points out it is the result of a variation -- a mutation -- in the AS3MT gene. The fact that it is passed on to offspring confirms this.

[shunyadragon]

I get the distinct impression that the three of you just said the same thing in different ways.

No 'selective breeding' describes human influence improve species, sub-species, and varieties to increase the benefit for human consumption and use. Evolution and natural selection is the response species to evolve, change and diversify into new species in response to natural pressures, and opportunities for expansion into new environments.

[TheLurch]

why is it a mutation and not a natural variation. If a group starts killing off everyone who is not blond, eventually all the nonblonde genes will be bred out and the population will all breed blonde.

There's not a sharp line between the two. Take lactose tolerance. There's evidence that it's arisen 4 different times in different pastoral populations. Spreading from them, it's become a natural variation in most populations. But when it first appeared, it was a mutation - a change in the DNA that alters function.

[rogue06]

Here's a short list of some of the beneficial mutations in humans that scientists have discovered known to have effected humans as a whole or particular groups that I came up with (I'm sure there are are many I missed):

1. Let's start with the Glycophorin A somatic cell mutation which has been found in most Tibetans (87%) and rarely in their Chinese neighbors (9%). This mutation controls red blood cell production and enables them to endure extensive periods at altitudes above 7,000’ (2133 meters) without succumbing to apoplexia.

This particular example has been touted by some as representing the strongest instance of natural selection ever documented in a human population and took place in the 2,750 years since the populations split though I think the apoA-I Milano allele mutation (see #10) might be better documented.

2. A similar though different mutation has also been identified among native people living at high altitudes in the Andes. In the South American case the adaptation involves making more red blood cells, which transport oxygen to the body's tissues. For example, native people in the Peruvian Andes have higher red blood cell counts than their countrymen living at sea level.

There is yet another totally different mutation among the people native to the Ethiopian highlands that allows them to survive better at high altitude.

3. Another well known example of a beneficial mutation are those that provide lactase persistence (brought up by The Lurch in the post above). An allele conferring lactase persistence has evolved at least seven different times in the last 7000 years among pastoralist groups allowing adult humans to drink milk. This provides them with another source of food to consume that those who are lactate intolerant can not use. That would definitely come in handy during periods of decreased food supply.

4. Similar are mutations of the ADH enzymes that allow for the consumption of alcoholic beverages. While alcohol consumption (more specifically its over-consumption) is the cause of many societal ills, it provided an important benefit in early cultures. Alcohol is rich in energy, portable and is far less susceptible to spoilage than the materials that they were made from like grains in the case of beer. Moreover, it has a far lower pathogenic load than water in a pre-modern environments.

All of this means that the ability to drink alcohol allowed people to get nutritional value from food stuffs subject to spoiling or more difficult to transport. Again this is a distinct advantage over those who had no tolerance for alcohol in the time of food shortages.

5. A mutation in the FADS gene cluster that scientists thought took place some 85,000 years ago allowed humans to manufacture long chain polyunsaturated fatty acids from plant fats. This meant that early humans no longer had to rely on just one food source, fish, for brain growth and development and allowed them to be able to leave the region.

6. Yet another mutation that scientists think took place between 11-19 thousand years ago is the one that caused a decrease in pigmentation in the skin (caused lighter skin) allowing those in northern climates to increase their ability to manufacture vitamin D from sunlight.

Interestingly, a couple years ago researchers announced that evolution of skin pigmentation is still continuing strongly over the last 5000 years and fairly robustly too. The authors calculate a selective sweep of 2–10% per generation.

7. Then there is ccr5-Δ32 which changes cell surface receptors and confers a significant resistance to infection by HIV-1 and may also confer some resistance to small pox and some plagues. Interestingly it does cause a higher susceptibility to West Nile.

8. Another example of beneficial mutations are some of the family members from the village of Limone Sul Garda in northern Italy have a mutation which gives them better tolerance of HDL serum cholesterol. This mutation was traced to a single common ancestor living in the 1700's, but has now spread to dozens of descendants and as a result this family has no history of heart attacks in spite of their high-risk dietary habits.

Genetic samples from this family are now being tested for potential treatment of patients of heart disease.

9. And then there’s a family in the state of Connecticut who've been identified as having hyperdense, virtually unbreakable bones that’s been traced to a mutation that increased the function of a gene called LRP5. According to those examining the family, members with the mutation have bones reminiscent of Bruce Willis’ character in the movie “Unbreakable.”

Interestingly, a different mutation to the LRP5 gene has been linked to just the opposite effect – more brittle bones.

10. One of the best known mutations is the apoA-I Milano allele mutation that has effected the apolipoprotein A1 protein found in human High-density lipoprotein (HDL), the lipoprotein particle that carries cholesterol from tissues to the liver and is associated with significantly reducing cardiovascular disease (specifically clogged arteries, heart attack, and stroke). This particular mutation was first documented in 1980 among some villagers living in northern Italy, all of who are descendants of a particular 18th century man named Giovanni Pomarelli. Synethetic versions have been manufactured and are making their way to market.

11. And for yet another example we’ve also identified an emerging population of tetrachromatic women who can see a bit of the normally invisible ultraviolet spectrum. For instance, the artist Concetta Antico has a genetic mutation that gave her four types of cone cell classes in her eyes (normal color vision humans only have three cone cell classes) and that her fourth cone appears to absorbs wavelengths that are described as being "reddish-orangey-yellow." The uptake is that she can see up to one hundred times more colors than a normal human being. In a way that is like the difference between someone with normal vision and a color-blind person. Some studies estimate that approximately 1% of the world's population tetrachromatic.

12. A little over a year ago a paper was released in Science which explains why the Inuits (formerly referred to as "Eskimos"), despite a diet that is heavily dependent upon fatty meat and fish (a diet which has long been associated with an increased risk in heart attacks and stroke) have a relatively low rate of cardiovascular disease. It appears that they have adaptive genetic mutations that allow them to better process the fats that they eat. These mutations occurred within a cluster of genes that direct construction of enzymes called fatty acid desaturases (FADS).

13. And the one that gets evolution deniers all worked up are the various mutations that confer resistance to malaria. Nearly everyone is aware of the sickle cell allele which confers resistance to malarial infections if you carry one copy of the allele but causes sickle cell anemia if you carry two copies. It's a good example of balancing selection. And even those with sickle cell anemia are considerably more likely to survive long enough to reproduce than those suffering from malaria.

What many are not aware of is that there are other alleles which confer resistance. The HbC variant for hemoglobin confers roughly a 30% reduction in risk for malarial infection if you have one copy but a 93% risk reduction if you have two copies. The anemia resulting from the double copy of this gene variant is very mild in contrast to the debilitating effects of sickle cell.

Then there is the various types of Thalassemia. While they all have negative effects (bone deformities, and cardiovascular illness like anemia) it also confers a degree of protection against malaria (specifically, malaria caused by the protozoan parasite Plasmodium falciparum) and those with β-thalassemia apparently have some protection against coronary heart disease.

Finally, a single genetic mutation protects some African children from the deadly symptoms of malaria. The mutation occurs in the gene NOS2 that encodes an enzyme to produce the gas nitric oxide -- something that is present throughout the human body. The mutation is a polymorphism, a single letter change in DNA. It causes cells to ramp up production of the gas, which is thought to protect people against malaria.

Children in Tanzania and Kenya who have the mutation are much less likely to develop the disease than children who do not, with one study discovering that those with the mutation living in Tanzania were nearly 90% less likely to develop severe malaria than individuals without the mutation.

[Bisto]

No 'selective breeding' describes human influence improve species, sub-species, and varieties to increase the benefit for human consumption and use. Evolution and natural selection is the response species to evolve, change and diversify into new species in response to natural pressures, and opportunities for expansion into new environments.

Ah, blame that on my ignorance of that term. On the surface it read similar enough. Thanks for the clarification

[TheLurch]

3. Another well known example of a beneficial mutation are those that provide lactase persistence (brought up by The Lurch in the post above). An allele conferring lactase persistence has evolved at least seven different times in the last 7000 years among pastoralist groups allowing adult humans to drink milk. This provides them with another source of food to consume that those who are lactate intolerant can not use. That would definitely come in handy during periods of decreased food supply.

Wow, it's up to 7? I need to pay more attention.