CRISPR and Sickle Cell Disease

By: Devanga Dassanayake

Recently, CRISPR gene editing has been all over the news. A new sensational innovation that scientists and doctors hope can cure various forms of cancer! But CRISPR’s uses are not limited to cancer but also to larger fruit, malaria in mosquitoes, and the topic of today’s article: sickle cell anemia.

What is CRISPR?
Firstly, what is CRISPR? CRISPR is a natural function found to protect bacteria and archaea from incoming viruses. Natural CRISPR uses two functions. The first function is short snippets of repeating DNA sequences called “clustered regularly interspaced short palindromic repeats,” or CRISPRs.

The second function is the one most commonly used in CRISPR gene editing: Cas or “CRISPR-associated” proteins which are like scissors that cut up DNA. Cas proteins cut a piece of viral DNA and sew it into the bacterium’s CRISPR region, creating a chemical picture of the infection. These viral instructions are subsequently replicated into small RNA fragments. This molecule has several functions in our cells, but in the case of CRISPR, it interacts with a specific protein known as Cas9. The resultant complexes function as scouts, latching onto free-floating genetic material in search of a match to the virus. If the virus re-invades, the scout complex promptly detects it, and Cas9 quickly destroys the viral DNA. This sort of defensive mechanism is seen in many microorganisms.

Researchers in 2012 figured out how they can actually repurpose CRISPR to target viral DNA and any DNA in any organism. CRISPR then became a precise gene editing tool. But how exactly did scientists repurpose this naturally occurring sequence in the lab?

First, scientists design a “guide” RNA, this guide is similar to the viral RNA when CRISPR is used in microorganisms. Essentially, the Cas9 protein is attached to this guide and then injected into the DNA scientists wish to manipulate. The guide RNA guides the Cas9 to the target gene, where Cas9 takes its scissors and snips the DNA.

Once the DNA is cut off, the cell will attempt to repair it using a process called nonhomologous end joining. However, this process is extremely prone to errors and the newly connected gene can be absolutely unusable. The way scientists combat this is by injecting a “template” DNA with their CRISPR mix. This template helps cells to repair the DNA using a different process called homology-directed repair. This template DNA is essentially used as a blueprint to repair a broken gene, but it can also be used to insert a completely NEW one.

What does CRISPR mean for us? The ability to fix DNA errors means wonders to clinical science. CRISPR can help people with genetic diseases that have no cure to find a possible cure. CRISPR could cut out the genetic errors that cause these diseases. For example, in cystic fibrosis or the topic of today’s article: sickle cell disease.

What is Sickle Cell Disease?
Sickle cell disease (SCD) is a genetic disorder caused by a mutation in the HBB gene, which provides instructions to make the beta-globin subunit of hemoglobin.

Hemoglobin is basically a protein in red blood cells that carries oxygen throughout the body. In people with sickle cell disease, the mutation causes hemoglobin to form abnormally shaped red blood cells that can become stuck in blood vessels, leading to many complications including, restricted blood flow and tissue damage.

Sickle cell disease manifests itself in many ways and symptoms of the disease can include anemia, chronic pain, infections, stroke, and organ damage.

Sickle cell disease is most prevalent in sub-Saharan Africa, but it also affects people of African descent and those of Mediterranean, Middle Eastern, and Indian ancestry. The condition affects more than 6 million people worldwide. Every single year, there are at least 300 000 newborns born with sickle cell disease, 80% of these children are born in Africa.

Treatment is VERY limited and only about 15 percent of patients can be cured with a bone-marrow transplant from a healthy sibling. However, this treatment comes with risks and is not available to everyone with sickle cell.

How can CRISPR cure sickle cell?

There is a need for a new, cheap, and accessible cure for patients with sickle cell disease. Furthermore, we already know that CRISPR can essentially erase the “typos” in genes that cause these hereditary diseases. So how exactly can CRISPR do that for sickle cell disease?

Before understanding what CRISPR can do for sickle cell disease. We need to understand why sickle cell disease occurs on a cellular level. A genetic mutation causes sickle cell disease. Sickle-cell disease is caused by a single nucleotide alteration that changes the structure of hemoglobin, which is the protein that makes up 70% of a red blood cell. Hemoglobin normally floats freely within a healthy red blood cell, carrying oxygen throughout the body. The structure of hemoglobin is changed in sickle cell disease. The altered hemoglobin now latches together after delivering oxygen to cells, causing the formation of the red blood cell to shift from a malleable donut to a more rigid, stickier, sickle shape. These sickle-shaped cells clump together quickly, obstructing blood arteries.

How can CRISPR change this single nucleotide mistake? Previously, researchers have tried to directly alter the sickle cell mutation. But Dr. Haydar Frangoul and his team are trying something different. They noticed that babies in the uterus create a very high amount of fetal hemoglobin which is very efficient in transporting oxygen. However, when babies are born they switch from making fetal hemoglobin to Hemoglobin A or adult hemoglobin.

What does this mean for sickle cell disease? Well, in patients with sickle cell disease, the mutation is in Hemoglobin A itself. So when babies with sickle cell disease are in the uterus they do not experience any complications related to that disease, this can be attributed to the creation of fetal hemoglobin. Furthermore, we know that sickle-cell individuals with persistently high fetal hemoglobin levels do not often develop serious repercussions from their illness, and some of them are totally symptomless. There are actually sickle cell patients, particularly in Saudi Arabia and western Africa, who continue to have high amounts of fetal hemoglobin so they are not badly afflicted by the condition.

So, Dr. Frangoul and his colleagues started investigating ways to stimulate the red blood cells to produce a large amount of fetal hemoglobin, which can stabilize red blood cells and keep them from sickling. They then realized that the gene responsible for this switch from fetal to adult hemoglobin is the BC11A gene. BC11A tells your stem cells to stop making fetal hemoglobin.

Therefore, they concluded that they can actually use CRISPR to cut out BC11A and force the body to make fetal hemoglobin once more. Dr. Frangoul and his team have already implemented this gene editing technology with sickle cell patients. These patients have noted their extreme pain caused by sickle cell disease disappears within weeks of their treatment.

The use of CRISPR in the treatment of sickle cell disease represents a big step forward in the area of gene editing. Achievements in curing sickle cell disease provide new hope for sickle cell disease sufferers and may pave the way for the development of similar gene treatments for other inherited disorders. As scientists continue to investigate the potential of gene editing, we may anticipate future developments in this field that might change the way we approach the treatment of genetic illnesses.

The inequity of CRISPR and sickle cell disease?
Unfortunately, with every medical innovation comes numerous problems and CRISPR is not immune to this. In what ways does inequity play a role in CRISPR research?

Firstly, in terms of the sickle cell research described above, it is very very expensive. Delivering a customized medication like this CRISPR cure from a trial site to where it is most needed throughout the world will be a huge task financially. Nowadays, newborn screening is required to care for sickle-cell disease, and it must be complemented with comprehensive treatment anchored in a sickle-cell disease specialty facility. These public health measures are effective, and they should be implemented first, but that does not mean that CRISPR research is unnecessary. That simply indicates that gene editing needs to be improved to have a future in low-resource situations; these improvements must make this CRISPR cure more technologically accessible, less expensive, and safer.

Secondly, the inequity of CRISPR manifests itself in terms of race. As previously stated, you must use a guide RNA before editing the gene. CRISPR may not make the desired cut if the guide RNA does not closely match the genome being edited. When CRISPR is used to modify human genes, this causes issues. It faces significant difficulties because human genomes differ individually and by ancestry, as opposed to lab mice, which are genetically identical. Because of this issue, CRISPR does not always edit human genomes as intended, especially in people of African descent, whose genomes differ the most.

Furthermore, recent studies have raised concerns about the use of CRISPR technology in the treatment of diseases that disproportionately affect certain ethnic groups. Scientific research has shown that ancestry mismatches can cause CRISPR to make incorrect cuts in the genome. This is especially problematic when using CRISPR to treat sickle cell disease, which primarily affects people of African descent. Off-target cuts caused by ancestry mismatches could potentially lead to cancer in such cases.

According to scientists, the implications of this CRISPR ancestry problem are far-reaching. The exclusion of diverse populations from genomics research will inevitably contribute to cancer health disparities. This issue emphasizes the need for greater diversity in genomics research in order to develop treatments that are effective for all ethnic groups. Inaction on this issue could lead to unequal access to potentially life-saving therapies, exacerbating existing health disparities.

Ultimately, CRISPR gene editing technology has the potential to transform medicine, notably in the treatment of hereditary illnesses such as sickle cell anemia. CRISPR allows scientists to repair DNA faults that cause genetic disorders by targeting and cutting the DNA at a precise site, then repairing the damaged gene with template DNA. This method has the potential to treat sickle cell anemia, a genetic condition that affects millions of individuals worldwide, by replacing the defective HBB gene with a repaired form. Although there are still ethical issues about using CRISPR in people, the advantages of discovering a low-cost and easily accessible solution for sickle cell disease cannot be overlooked. As technology continues to advance, researchers and doctors should proceed with caution, but also with a sense of optimism about the possibilities it holds for the future of medicine.

Works Cited

Henle, Andrea, director. How CRISPR Lets You Edit DNA . YouTube, TED-Ed, 24 Jan. 2019, https://youtu.be/6tw_JVz_IEc. Accessed 12 Mar. 2023.

Kaiser, Jocelyn. “CRISPR’s ‘Ancestry Problem’ Misses Cancer Targets in Those of African Descent.” Science, Science, 21 Nov. 2022, https://www.science.org/content/article/crispr-s-ancestry-problem-misses-cancer-targets-those-african-descent.

Nature, director. Can CRISPR Cure Sickle-Cell Disease? YouTube, Nature Video, 25 Aug. 2021, https://youtu.be/mQ8Ola_C5po. Accessed 12 Mar. 2023.

“Sickle Cell Disease.” World Health Organization, World Health Organization, https://www.afro.who.int/health-topics/sickle-cell-disease.

“What Is Sickle Cell Disease?” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 18 Aug. 2022, https://www.cdc.gov/ncbddd/sicklecell/facts.html.

“What Is Sickle Cell Disease?” National Heart Lung and Blood Institute, U.S. Department of Health and Human Services, 22 July 2022, https://www.nhlbi.nih.gov/health/sickle-cell-disease.