The CrispR revolution

Emmanuelle Charpentier and Jennifer Doudna have just won the Nobel Prize for Chemistry. They have been my picks for the prize for years now. Nobel Prizes are often awarded decades after the fact, but CrispR has been such an obvious winner that it is a surprise it took until 2020 to be awarded. (Largely, I guess, due to the politics of several competing claims and patents, that have been going through the courts). 

This Noble is a well-deserved recognition of one of the seminal breakthroughs in biology of the last several decades. The award recognises elegant basic biological experiments that identified a novel immune mechanism that bacteria use to fight off viruses. The key insight is that the chemistry of this system allowed simple modifications to rewire this bacterial system into a tool to edit the genome of essentially any living being. A striking example of blue-skies research on basic science having an incredible translational effect. The CrispR system ranks up there with identifying the structure of DNA or the sequencing of the human genome - indeed, for the first time it allows us to really use the information gained by these earlier revolutions. CrispR tools are used daily across the globe to create new vaccines, generate gene therapy, design bacteria to help industrial processes. Essentially, the discovery of CrispR as a genome-modification tool has put biology on steroids - dramatically accelerating the pace of both basic research and translational applications

SARS-CoV-2 is not a bioweapon

Coronavirus science simplified: number 5. This article in Nature Medicine used genetic analysis to test the hypothesis that SARS-CoV-2 was generated in a lab as a bioweapon. Spoiler alert: it wasn't. Clear hallmarks of natural evolution and none of the features of a designed virus. Read the original paper, or see the illustrated abstract by Tenmai.

The genetics behind immune system variation

Our immune systems are incredibly diverse. How much of that diversity is due to our genes?

Each of our immune systems acts a little bit differently. Environmental factors have an impact, but so do our genes. A team of researchers in Leuven went looking for links between more than 10 million genetic variations and more than 50 immunological traits. Their findings help to explain why some people have a higher risk for immune diseases than others.

Our immune systems are molded by our unique genetic make-up. Add to that a complex mix of environmental drivers, and you get an enormous functional diversity. From an evolutionary point of view, this diversity is essential to minimize the chance that a pathogen could wipe out an entire population.

But the flip-side is that we’re also greatly diverse when it comes to susceptibility or resistance to a broad range of diseases – not only those with an obvious immunological component, such as autoimmunity, allergy, inflammation and cancer, but also those with a more indirect link to immune-deregulation, such as cardiovascular, metabolic and neurological diseases.

A genome-wide survey

While scientists have studied the links between genetic variations and a whole range of different diseases, the characterization of this “genotype-phenotype relationship” for the immune system itself has received far less attention.

That is why a team of scientists led by An Goris (KU Leuven) and Adrian Liston (VIB-KU Leuven) undertook a large genetic study with almost 500 participants. In a so-called genome-wide association study, or GWAS, they probed more than 10 million genetic variations, spread out across the genome, for links to 54 different traits relevant to adaptive immunity. This allowed the researchers to determine which genetic variants were, for example, typical for people with high or low levels of different pro- or anti-inflammatory cytokines.

“We found eight previously unknown associations,” says An Goris, lead geneticist of the study. “The strongest connection was for a genetic variant present in only 2% of the study participants.” All of the identified genetic associations provide important biological insights into what drives variation in our immune systems.

This is only the tip of the iceberg, according to Goris: “What we know now, explains about 10% of the variation, but we are still in the initial discovery phase. There might be many more genetic variants—including relatively rare ones—that affect our immune response and thus our susceptibility to certain diseases.”

Helping to map disease risk and refine treatment

Mapping how genetic variants affect immune function will not only help us understand disease mechanism better, it should also help to refine treatment options.

“The clearest example is the clinical implication offered by genetic variation in the RICTOR gene,” explains Adrian Liston, lead immunologist on the study. “We now know that RICTOR changes the production of a cytokine called IL-4, providing a new therapeutic target for treatment of autoimmune diseases and asthma.”

In many cases, the effects are more subtle and indirect, adds Liston: “Most people will carry dozens of genetic variants that may skew the immune system in a particular direction. This accounts for part of the reason why different people have different risks for immune diseases, but we are much more than the sum of our genes.”

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Lagou et al. 2018 Cell Reports. 'Genetic architecture of adaptive immune system identifies key immune regulators'.

Journal club: The effect of gender (not sex!) on the genome

One of my pet peeves is when scientists use "gender" (i.e., identity) when they actually mean "sex" (i.e., anatomy). It is typically done to avoid embarrassment, but it is imprecise, and the difference can be important. The short-cut for gender vs sex is usually "sex is biological, gender is cultural", but this short-cut is also wrong, since culture can impact on biology.

Take this Nature Genetics paper, from the Gibson lab. They looked at eQTLs in human blood, which is basically the effect of genetic variation on gene expression. The study was performed on Berbers in Morocco, in both a modern urban setting and a traditional rural setting:

 

When looking at gene expression changes in men and women from urban areas (green and blue, below), there is basically complete overlap between men and women. However when you look at the rural traditional areas, with strict cultural separation of men and women (red, below), there is almost complete separation between the men and the women at the transcription level.

In short, men and women are biologically different only because of the gender roles imposed in the rural setting! The social construct of gender can actually substantially change our biology. A good reminder that whenever we see an effect in humans that we think is due to sex, we need to remember that it could actually be an impact of imposed culture.

Read the full paper: Idaghdour et al, "Geographical genomics of human leukocyte gene expression variation in southern Morocco", Nature Genetics 2010. 42(1):62-7

MutaMouse is open!

MutaMouse, our new genome engineering Core Facility, is now open! Come talk to us about making KO or KI mice for you!

MutaMouse Core Facility

Visit our website and found out what we can do for you!

Understanding variation in the human immune system

My talk from the recent Eppendorf Young Investigator Award ceremony on variation in the human immune system.

Journal club: Genetics breaks the relationship between obesity and diabetes

Samoans tend to be physically large people, with a very strong build in addition to being at high risk for obesity. More than 50% of Samoans are obese, one of the highest rates in the world. A recent paper in Nature Genetics mapped this susceptibility to obesity to a mutation in CREBRF (p.Arg475Gln), which is common in Samoans and very rare in the rest of the world. This gene is extremely potent, the strongest obesity-causing polymorphism yet found.

Samoans also have one of the highest rates of type 2 diabetes in the world, so it is very easy to point a finger and assume that CREBRF causes both obesity and diabetes. Intruigingly, this is wrong - CREBRF (p.Arg475Gln) drives obesity but actually protects against diabetes! 

Increasingly, the theoretical correlation between BMI and diabetes seems to be breaking down. China is having both an obesity and diabetes epidemic, with the transition to a Western diet, but in China there is essentially no correlation between BMI and diabetes. It is starting to look as if diet drives these two phenomenons independently, and diabetes is not simply a consequence of obesity.

Read the article: Minster, R.L. et al. 'A thrifty variant in CREBRF strongly influences body mass index in Samoans'. Nature Genetics 48, 1049–1054 (2016).

The Genetic Components of Rare Diseases

Last fall, the conclusion of the 1000 Genomes Project revealed 88 million variants in the human genome. What most of them mean for human health is unclear. Of the known associations between a genetic variant and disease, many are still tenuous at best. How can scientists determine which genes or genetic variants are truly detrimental?

Patients with rare diseases are often caught in the crosshairs of this uncertainty. By the time they have their genome, or portions of it, sequenced, they’ve endured countless physician visits and tests. Sequencing provides some hope for an answer, but the process of uncovering causal variants on which to build a treatment plan is still one of painstaking detective work with many false leads. Even variants that are known to be harmful show no effects in some individuals who harbor them, says Adrian Liston, a translational immunologist at the University of Leuven in Belgium who works on disease gene discovery.

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Read more in The Scientist