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Medical Genetics and Race (light)

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Misty Mistyy

on 9 March 2016

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Transcript of Medical Genetics and Race (light)

The amount of variation between humans….
Compared to other animal species, humans are much less diverse.
Example from Richman- 4x’s less diverse than chimpanzees.
In fact, humans are 99.9% identical, meaning that two humans differ at 0.1%.
within racial groups, (not between them), over 85% of human variation is found, suggesting there is more human variation within a population (or racial group) than between populations.
So human variation is insignificant then, right?
•Are we sure that 15% variation is negligible?
Actually, two humans differing at 0.1% means that they differ in about 3 million of their 3 billion nucleotides.
Morphological differences among humans that seem to align with geographic patterns (Skin tone, height, body shape…)
There are also differences of frequencies of certain alleles, such as disease-causing alleles, reactions or immunities to diseases, to plants, to medical treatments between populations….
This is what is discussed in Genetic Influences on Health. Does Race Matter?
Medical Genetics & the Concepts of Race
Human variability is real and despite its history spattered with racism and other stigmas, can provide important information and and medical implications that can be used in a positive way.
But if race has caused some of the most terrible atrocities in history , why defend it ?
"What argument against social change could be more chillingly effective than the claim that established orders with some groups on top and others at the bottom, exist as an accurate reflection of the innate and ungchangeable intellecutal capacities of people so ranked?" (p 28, Gould)
Carolus Linnaeus- discrete ranked races
physical characteristics, temperament, means of government
4 part taxonomy
white Europeans
red Americans
yellow Asians
black Africans
dominant racial classification today among lay people and government administrators,
Caucasoids
Mongoloids
Australoids
Negroids
Capoids
Early work on blood proteins by Richard Lewontin and others showed that human variation was much more complicated and continuous than a simple five or six race matrix could reflect.
14kya maximum human genetic diversity
The original human population expanded (within and then outside Africa).
There was a separation into sub-populations which evolved to meet climatic changes. Resulting in genetic drift (change in frequency of an allele), thus genetic differences .
Decrease in human genetic diversity
population consolidations
technological developments
wars
conquests
nationfounding
colonizations
epidemics
localized extinctions
slave trading
Eventually we created a six-part taxonomy










Diagnostic physical characteristics
Those who don't possess key traits are disqualified
Variation from the norm= exceptions or admixtures
Europeans
Americans
Asians
Africans
Australians
Oceanians
Human variation is much more complicated.
Continuous divisions,
No genetic or morphological feature is possessed by all members of a particular race and absent in all members of other races.
A short history of variation
African
European
Asian
Concepts of Race
Sociocultural
Biological
The socio-cultural concept of race
Used by government
Argued to be helpful for implementing affirmative action and other programs to ameliorate past conditions of racism.
Used on birth certificates, for census, for scholarships, etc.
Here's what biology has taught us about race
The human genome is replicated in every cell
46 chromosomes (23 pairs) in each cell
Each chromosome is made of a bound up double strand of DNA.
These strands are composed of millions of nucleotides (cytosine, guanine, adenine, and thymine )
The order of these nucleotides codes for information to construct the cells that make a human.
Human genome ~ 3 billion nucleotides- no two humans have the same set of sequences.
Human genetic variation would be a difference between two people of one nucleotide at a particular location. Aka a single nucleotide polymorphism, or SNP.

Through mutation, these sequences can change slightly and these changes are known as variation.
Through mechanisms that separate populations, certain mutations become more or less frequent in each population.
You can see how different populations can develop different frequencies of variations
10-15% of human genetic variation is explained by differences between sub-Saharan Africans, Northern Europeans, and East Asians.
According to Bamshad
Although variation between groups is small, it is “highly structured (allele frequencies at different loci are highly correlated) so that a modest number of genotypes (ie, several hundred per person) can, with a high degree of accuracy, allocate anonymous individuals to groups that correspond to ancestry from different geographic regions” (Figure 2C)
Individuals from different populations are less alike than those from the same population Fig A and B)
Now we're starting to see how race can be important.
"The clusters fascinate and have provoked so much discussion because they are the closest analogues to traditional races for which there is any biological support; “race-lite,” if you will. Race is a social construct, but the clusters are real biologically; their “reality” consists in their ability to capture, accurately but at low resolution, about half of the 15% of human genetic variation that can be attributed to geography."
We can extract important information from racial group
Variants influencing risk for diseases such as diabetes, hypertension, infections such as AIDS, are only common in a single population, or the frequency among groups is significantly bigger.
For example, an allele associated with obesity and hypertension varies in frequency with 80% in Africans, 45% in Asians, and 30% in Europeans.
A recent study by Tate and Gooldstein found that out of 42 gene variants that were associated with drug responses, over 2/3 of the gene variants showed a significant difference in frequency between African and European Americans.
So we can speculate about how often to expect certain risk variants depending on geographic ancestries
VS
Misidentification of racial group.
These racial categories might only work in the US
Environmental effects
Alternatives to race -Genetic testing
Real medical implications that can be inferred through race
What if you don't know about your ancestry
What if you have an incorrect idea about your ancestry?
Some people do ineeed misidentify themselves as the incorrect race [VIDEO]
This can lead to seriuos misdiagnoses

This is sort of an anomaly, however
Studies show that humans are pretty good at self-identifying into racial groups.
(Tang et al) 3636 self-identified ancestry as European, African, Hispanic, or Asian.
Only 5 people’s results differed from genetic data.
However, these were people in the US, (immigration to the US is less than 10 generations old, so the dynamic of the US is different than other areas in the world)
So this might not work so well in other places
Those with African or Asian ancestry living in areas besides the US, such as Europe or South America are more heterogenous.
Some populations from East Africa and West Africa are more genetically diverse than populations from N. Europe and E. Asia.
There is a lack of data from multiple racial groups, Africa being one of the major areas.
DTC Genetic testing
Increasingly popular public genetic ancestry testing (direct-to-consumer, DTC)

Certain ancestry information provided by these tests assign a user levels of ancestry that are not well defined or identified.
Furthermore, different marker systems for different parts of the genome can result in varied information about ancestry. There is still limited information about human population groups which can lead to limited accuracy of ancestry inferences.
unadvertised lack of quality assurance
anxieties about results these tests might produce socially, possibly with the promotion of stigmatized or discriminatory human subdivision.
Population geneticists and anthropologists use genetic markers and other comparative datasets similar to those used in these DTC ancestry testing agencies
However geneticists and anthropologists' speculations are usually always made at the population or group level, while commercial ancestry testing is made at the individual level, where ancestry estimation is much less apparent.
Useful collections of human populations, such as the HGDP (Human Genetic Diversity Panel), are convenient and often referred to by DTC programs, but these collections do not sample densely within any one geographic region.
Some ancestral populations are missing altogether
Because of this, inferences within and among regions are limited.
A large number of single-site changes have served as the basis for breaking Y chromosomes into different "haplogrpoups"
So, Y chromosomes within, say haplogroup C are more closely related to one another than to a Y chromosome from haplogroup J.
Thus if two men both carry haplogroup C Y chromosomes, they are more likely to share a paternal lineage than if they had different haplogroups. Even so, this relationship does not mean that they are more genetically similar overall.
What if someone wants to use DTC genetic testing with their healthcare provider to factor into their care?
In doing this, it is important to also take into consideration other factors such as social, personal, and environmental factors.
Ethics, Epidemiology and the Thrifty Gene: Biological Determinism as a Health Hazard
Thrifty genotype-explanation of recent epidemic of diabetes in the world.
Thrifty genotype- suggests that the diabetic genotype encourages a frugal or "thrifty" use of food, which would obviously be helpful during food shortages. Today, with food being more high energy and plentiful, this thrifty genotype is not only no longer advantageous, but hazardous to health.
But is this epidemic of diabetes really determined by genetics? This article argues that despite much time looking for genetic markers for NIDDM (non-insulin dependent diabetes), no genes for NIDDM have been found.
It is suggested that perhaps diabetes is influenced by other factors.
Supporting evidence
Has a biological or genetic basis
Lewontin (American evolutionary biologist, geneticist, academic and social commentator)
Quoted by many anthropologists, many geneticists.
Known for saying "Race is not real"
Human variation was so minute that it should be dismissed.
Because of his efforts, progress dealing with human variation was severely stifled.
"What argument against social change could be more chillingly effective than the claim that established orders with some groups on top and others at the bottom, exist as an accurate reflection of the innate and ungchangeable intellecutal capacities of people so ranked?" (p 28, Gould)
Richard Lewontin (American evolutionary biologist, geneticist, academic and social commentator)
Known for saying "Race is not real"
Quoted by many anthropologists, many geneticists.
Human variation is so minute between populations that it should be dismissed.
Because of his efforts, academic progress and research dealing with human variation has been severely stifled.
The ideas in the Bamshad paper that we're reading are still not accepted by most academics in Bamshad's department at Washington University, partly due to the influences of Richard Lewontin.
This guy thinks so
Figure A
Network of genetic relatedness among individuals.
genotyped for 250 coding SNPs
length of branch proportional to genetic distance between individuals and populations
distance between any 2 circles of same color=high within-population variance
distance between clusters (dotted lines)= small and reflects low between-population variance.
Figure B
Genetic distance between individuals is reflected by the sum of the branch lengths between individuals.
Despite high within-population variance, individuals from different populations are, on average, more different from one another than individuals from the same population.
Figure C
Circles represent inferred ancestry proportion for individuals
The distance of each circle to an apex is proportional to the degree of ancestry in African Americans, Asian Americans, or European Americans.
The degree to which the circles are clustered within a population reflects the degree of admixture and structure within a population.
The circles representing African Americans are less tightly clustered because the proportion of ancestry among individuals is more varied than in Asian Americans and European Americans.
A study by Barker et al showed that poor nutrition and growth in utero or early infancy carry a significantly increased risk of diabetes (NIDDM) and cardiovascular disease later in life, especially when weight gain in adulthood is added to early undernutrition.
Genetic Influences on Health. Does Race Matter
Bamshad
1000 Genomes Project Finds Substantial Genetic variation Among Populations
Kuehn
Inferring Genetic Ancestry: Opportunities, Challenges, and Implications
Royal et al
Ethics, Epidemiology and the Thrifty Gene: Biological Determinism as a Health Hazard
McDermott
Race is useful for biomedical research and medical treatment
Race isn't as precise as geographic or genetic ancestry
genetic factors which influence common traits related to health can vary among populations
racial groups can sometimes be adequate enought to identify risk factors for disease and responses to treatment in the US
There is an overall need for a more varied and random sampling of human variation across the genome
Features a study that is the most comprehensive catalog of human genetic variation, involving 1,092 genomes of healthy individuals from various regions around the world
Findings show that there is substantial human variation among populations (same as Bamshad)
Study is said to capture an estimated 95% of human genetic variation
provides comparative information for researchers studying the role of genetics in disease and clinicians using genomic technology to find a genetic cause for a medical condition.
This project also helped speed up techniques for sequencing
Discusses the increasingly popular genetic ancestry testing for the public
certain ancestry information provided by these DTC providers assign a user levels of ancestry that are not well defined or identified (individual instead of population group)
limited information about population groups- calls for more sampling in terms of ancestral referencing
wants DTC testing companies to inform their customers about lack of certainty for some results
Concerned about social implications of genetic testing- issues of racism, defining nationality, identifying criminals...
what about the privacy of these databases--will your personal information be shared, and perhaps used against you for health insurance, for example
No quality assurance guarantee- makes them wonder if they should issue lab certification or accredidation
•What if someone wants to share DTC ancestry test results or ancestry-related estimates of disease risk with their healthcare providers and expect that the information be factored into their care.
What if this is used against you for health insurance?
•How might genetic testing affect cultural, religious, social, historical, and political processes that explain origin as well as group membership, identity, and rights?
What about the use of ancestry test results to make claims for benefits through affirmative action or for rights perceived to be associated with their new-found Native American status?
What about DTC-ancestry-test takers in seeking dual citizenship in countries identified as their ancestral homelands?
•Is a sociocultural idea of race beneficial? Does it help us ramify past racial crimes, or does it just foster current incorrect ideas about race?
•Why is race so interesting, why has it persisted for so long?
•What are your opinions about human variability and race? Which does and does not exist and why?
•If race is a socially constructed concept, then why are we able to self-identify in a racial category which matches up rather well with genetic data?
What is your opinion about environmental factors vs genetics?
Thrifty genotype-explanation of recent epidemic of diabetes in the world.
Thrifty genotype- suggests that the diabetic genotype encourages a frugal or "thrifty" use of food, which would obviously be helpful during food shortages.
Today, with food being more high energy and plentiful, this thrifty geotype is not only no longer advantageous, but hazardous to health.
But is this epidemic of diabetes really determined by genetics? This article argues that despite much time looking for genetic markers for NIDDM (non-insulin dependent diabetes), no genes for NIDDM have been found.
It is suggested that perhaps diabetes is influenced by nutrition and diet.
This graph shows how race is a good indicator for medical treatments

This is an example of a hypothetical drug that lowers blood pressure.
Responses to this drug are shown in the graph, and the mean differences between European Americans and African Americans is quite different. This is perhaps due to a genetic risk variant.
The graph shows that If this drug was given to everyone, we can see European Americans would benefit only a little from it, whereas African Americans would get much more benefit from it.
With this sort of information, we can eliminate unnecessarily prescribing medication to a large group of people, while making sure a lot of other people are benefiting.
What does this mean medically?
So race can be helpful medically, but what other factors are should we consider?
In the absence of genetic tests and geography, race is the next best proxy
we can see variation within populations is high
but we can see that the variation between populations is even greater.
Figure B helps explain that.
distance between clusters (dotted line)
Full transcript