1.  Introduction

What if a disease could be treated by correcting the DNA responsible for it rather than managing its symptoms throughout a person's life?

That is the promise behind CRISPR gene editing (Clustered Regularly Interspaced Short Palindromic Repeats), one of the most important developments in modern biotechnology. CRISPR allows scientists to make targeted changes to DNA, potentially switching off harmful genetic instructions, correcting certain mutations, or changing how a gene behaves.

Unlike conventional medicines that are often taken repeatedly, some gene-editing therapies are designed as a one-time treatment that can produce long-lasting effects. However, this does not mean CRISPR can currently cure every genetic disease. The technology remains under active development, and its benefits, risks, cost, and availability vary considerably by disease and country.

The field has already moved beyond laboratory research. In December 2023, the U.S. FDA (U.S. Food and Drug Administration) approved Casgevy, the first FDA-approved therapy using CRISPR/Cas9 technology, for eligible patients with sickle cell disease. The FDA subsequently expanded its indication in 2026 to include younger patients and transfusion-dependent beta-thalassemia.

So, how does CRISPR work? What diseases can it treat? How successful is it? And could ordinary people eventually have access to gene editing?

Let's explore the technology in simple terms.

2.  What Is CRISPR Gene Editing?

CRISPR gene editing is a technology that enables scientists to make precise changes to DNA.  DNA can be thought of as the biological instruction manual inside our cells. Genes are sections of this instruction manual that provide instructions for producing proteins and regulating biological processes.

A genetic disease can occur when a gene contains a harmful mutation or when a genetic sequence causes cells to behave incorrectly.  CRISPR provides scientists with molecular tools that can locate a chosen DNA sequence and make a change at or near that location.

The most widely known system is CRISPR-Cas9. CRISPR stands for "clustered regularly interspaced short palindromic repeats," while Cas9 is an enzyme that can cut DNA.

The World Health Organization describes genome editing as a method for making specific changes to DNA, including adding, removing, or altering genetic material.

The significance is enormous: instead of only treating the consequences of a genetic disorder, researchers can potentially intervene much closer to its biological cause.

3.  Working of CRISPR Gene Editing

CRISPR can sound complicated, but its basic concept is relatively easy to understand. 

Imagine DNA as an enormous document containing billions of characters. Researchers first identify the particular genetic sequence they want to modify.

A simplified CRISPR-Cas9 process involves several stages.

a. Identifying the Target

Scientists determine which DNA sequence is associated with the disease or biological function they want to change.

b. Designing a Guide

A guide RNA (gRNA) is designed to direct the CRISPR system toward a particular DNA sequence.

Think of the guide as a GPS system that helps the molecular machinery find its destination.

c. Reaching the DNA

The CRISPR components are delivered into the relevant cells. Depending on the treatment, editing may happen inside the body or in cells removed from the patient.

d. Making the Edit

Cas9 can cut the targeted DNA. The cell then repairs the break.  Scientists can exploit this repair process to disrupt a harmful sequence or make a desired genetic change.

e. Producing the Biological Effect

If the editing works as intended, the altered cells may behave differently. In some therapies, the goal is to produce a useful protein or restore a healthier biological process.

This is why CRISPR is sometimes described as a molecular "editing tool" rather than simply a conventional medicine.

4.  Its Approach

There is no single approach to CRISPR gene editing. The strategy depends on the disease and the cells that need to be changed.

i.  Ex Vivo Gene Editing

In an ex vivo approach, cells are removed from the patient's body and edited in a laboratory.  The modified cells are then returned to the patient.

This approach is particularly useful when scientists can collect and manipulate blood-forming stem cells.

Casgevy, for example, uses a patient's own blood stem cells. The cells are edited outside the body and subsequently infused back after the patient receives conditioning treatment. Research published in The New England Journal of Medicine described the therapy as CRISPR-Cas9 editing of autologous blood-forming stem and progenitor cells.

ii.  In Vivo Gene Editing

With in vivo editing, the gene-editing machinery is delivered directly into the patient's body.  This approach could eventually be particularly useful for tissues that are difficult to remove and manipulate outside the body, such as certain organs.

However, delivering the editing machinery to exactly the right cells remains one of the major scientific challenges.

5. What Is CRISPR Gene Editing for?

CRISPR gene editing is being investigated for a wide range of medical applications.

These include inherited blood disorders, certain cancers, rare genetic diseases, metabolic disorders, neurological conditions, and other diseases.

One of the most important applications is treating diseases caused by genetic mutations.  For example, sickle cell disease affects haemoglobin and can cause severe pain episodes, anaemia, and organ complications. Rather than correcting the original sickle-cell mutation directly, the CRISPR-based Casgevy treatment edits a regulatory region associated with BCL11A to increase foetal haemoglobin production.

This illustrates an important point: gene editing does not always mean repairing the exact mutation that originally caused a disease. Sometimes changing another genetic pathway can compensate for the harmful effect.

6.  Its Success Rate

There is no single "CRISPR success rate."  Success depends on the disease, the editing method, the target cells, the delivery system, and how researchers define success.

However, the results from some clinical studies have been remarkable.  In a phase 3 study of exagamglogene autotemcel (generic name for a breakthrough gene-editing therapy), the CRISPR-based treatment later marketed as Casgevy, 29 of 30 evaluable patients with severe sickle cell disease—about 97%—were free from severe vaso-occlusive crises for at least 12 consecutive months. All 30 evaluable patients were free from hospitalization for severe vaso-occlusive crises for at least 12 months.

The FDA's original approval assessment similarly reported that 29 of 31 evaluable patients, or 93.5%, achieved freedom from severe vaso-occlusive crises for at least 12 consecutive months during the specified follow-up period.

These numbers are encouraging, but they should not be interpreted as meaning that "CRISPR cures 97% of genetic diseases."

The studies involve specific diseases, carefully selected patients, and particular treatment protocols. Long-term follow-up is also essential because gene editing can produce effects that may take years to fully understand.

7.  Diseases Cured or Treated Using Gene Editing

The word "cured" needs to be used carefully.

CRISPR has demonstrated the ability to produce potentially transformative, long-lasting treatment outcomes for certain diseases, but scientists cannot yet claim that all CRISPR-treated diseases are permanently cured.

a.  Sickle Cell Disease 

Sickle cell disease (an abnormal red blood cell of crescent shape) is one of the clearest examples of successful clinical CRISPR treatment.

Casgevy is approved in the United States for eligible patients with sickle cell disease involving recurrent vaso-occlusive crises.  The treatment aims to increase foetal haemoglobin, reducing the tendency of red blood cells to sickle.

b.  Transfusion-Dependent Beta-Thalassemia

Beta-thalassemia is another inherited blood disorder for which Casgevy has received regulatory approval. Patients with severe beta-thalassemia may require repeated blood transfusions. The gene-editing approach aims to restore the body's ability to produce healthier levels of functional haemoglobin.

The FDA (U.S. Food and Drug Administration) currently lists Casgevy as indicated for transfusion-dependent beta-thalassemia as well as specified sickle cell disease patients.

c.  Other Diseases Under Investigation

Researchers are studying gene-editing approaches for many other conditions, including some cancers, immune disorders, rare genetic diseases and neurological conditions.

However, many of these applications remain experimental.

For example, ClinicalTrials.gov contains ongoing studies investigating CRISPR-based approaches for conditions including Duchenne muscular dystrophy and rare neurological disorders.

Therefore, patients should distinguish between an approved treatment and a clinical trial. A promising laboratory result does not automatically mean that a therapy is ready for routine medical use.

8.  Benefits for Humanity

The potential benefits of CRISPR gene editing extend far beyond individual patients.

i.  Potentially Long-Lasting Treatment

A successful gene-editing intervention can potentially produce effects that last for many years because the genetic change occurs inside cells.

ii.  Treatment at the Biological Source

Traditional medicines may control symptoms. Gene editing can potentially intervene closer to the underlying biological mechanism.

iii.  New Possibilities for Rare Diseases

Many rare genetic diseases have limited treatment options. CRISPR could provide a way to target diseases that previously had no practical molecular treatment.

iv.  Reduced Treatment Burden

If a one-time or infrequently administered therapy successfully controls a disease, patients could potentially spend less time receiving repeated treatments.

v.  Advancement of Medical Research

CRISPR is also a powerful research tool. Scientists can use it to understand how genes work and identify potential drug targets.

The WHO notes that genome editing could contribute to more targeted treatments and prevention of genetic disorders, while emphasizing the importance of safety, effectiveness, and ethics.

9.  Drawbacks and After-Effects

CRISPR is powerful, but it is not risk-free.

a.  Off-Target Effects

The editing system may sometimes affect DNA sequences other than the intended target. Researchers work extensively to reduce these unintended edits, but complete elimination of risk remains a challenge.

b.  Immune and Treatment-Related Risks

Patients may experience complications related to the delivery method or other parts of the treatment.

In the Casgevy clinical programme, several adverse events were associated with the conditioning regimen used before cell infusion.

c.  Long-Term Uncertainty

A genetic edit can potentially remain in cells for a very long time. Consequently, researchers need years of follow-up to understand long-term safety.

d.  High Cost

Advanced gene therapies can be financially inaccessible to many patients, raising concerns about inequality in healthcare.

e. Ethical Concerns

There is a major difference between editing the cells of an existing patient and editing embryos in a way that could affect future generations.

The WHO considers heritable human genome editing a particularly significant ethical and safety issue and has called for strong governance and oversight.

f.  Risk of Unregulated Treatments

The excitement surrounding CRISPR has created opportunities for misleading medical claims. A treatment advertised online as a "permanent genetic cure" should be approached with extreme caution unless it has undergone appropriate clinical testing and regulatory review.

10.  Conclusion

CRISPR gene editing represents a fundamental shift in medicine: from managing some genetic diseases toward potentially modifying the biological instructions behind them.

The technology has already reached clinical practice. Casgevy demonstrates that CRISPR-based treatment can produce substantial benefits for appropriately selected patients with sickle cell disease and transfusion-dependent beta-thalassemia, while ongoing research is exploring many additional conditions.

But CRISPR is not a universal cure, nor is it currently available to everyone.