CRISPR, Gene Editing and Gene Therapy: Ethics for Medical School Interviews

Gene editing changes a patient’s own DNA. UK law allows it in body cells, called somatic editing, but bans editing embryos, eggs or sperm to make a baby, because those changes pass to every future generation. Medicine interviews use gene editing to see whether you can argue an ethical case rather than recite the biology.

I'm Dr Akash Gandhi, an NHS GP, and I've prepared applicants for medical school interviews at TheUKCATPeople since 2012. The argument here is far more about ethics than biology, and our guide to answering medical ethics interview questions has that framework.

What is CRISPR gene editing?

CRISPR is a tool that finds a single sequence in a genome and changes it, and it's built from two components working together: a guide RNA that matches the target, and an enzyme, usually Cas9, that cuts where the guide lands. The guide is the satnav and the enzyme is the scissors.

• What it is for: rewriting a faulty sequence the patient has, rather than adding a gene the cell lacked from the start.
• Where it already exists: Casgevy, a CRISPR therapy for sickle cell disease and beta thalassaemia, funded by the NHS since January 2025.

Key Takeaway: CRISPR cuts DNA and the cell patches the break itself, which is why editing is powerful and unpredictable at the same time.

Is gene editing the same as gene therapy?

No, though they get used interchangeably all the time. Gene editing rewrites a sequence the patient already has, while gene therapy is the broader term that also covers adding a working copy of a gene and leaving the faulty one where it is. The table below is most of what you need.

If you're asked to name a gene editing therapy on the NHS, Casgevy is the one to reach for, and it's worth remembering that CAR-T adds a gene rather than editing one.

Key Takeaway: Casgevy edits, while Zolgensma and CAR-T add a gene, so both of those leave the patient’s own faulty sequence in place.

What is the difference between somatic and germline gene editing?

Somatic editing changes DNA in body cells, so it affects only that patient. Germline editing changes eggs, sperm or an early embryo, so the change appears in every cell of the resulting person and passes on to their children as well.

Key Takeaway: Say somatic or germline early, because germline editing raises a question medicine rarely has to face: what you owe someone who does not yet exist.

Is gene editing already available on the NHS?

Yes. Casgevy is the world’s first licensed CRISPR therapy, approved here in November 2023 for sickle cell disease and beta thalassaemia, in patients aged 12 and over.

NICE agreed the NHS should fund it, and NHS England expects around 50 patients a year. It goes to people with severe repeated crises and no matching marrow donor.

What's clever about it is that it doesn't fix the sickle gene at all, it works around it.

• The starting point: we're all born making fetal haemoglobin, which doesn't sickle.
• The switch: a gene called BCL11A switches fetal haemoglobin off after birth.
• What Casgevy does: CRISPR breaks that switch in the patient’s own blood stem cells, so fetal haemoglobin comes back on and does the job the adult version can’t.

Why is "cure" the wrong word for Casgevy?

Because of what it costs the patient to get there: chemotherapy to clear the marrow, four to six weeks in hospital, and a serious risk of infertility afterwards. A 12-year-old can be offered an end to a lifetime of crises at the price of never having biological children.

Beneficence says take the crises away, and non-maleficence points at sterilising a child. Autonomy is the hard one, because a 12-year-old cannot simply be asked, which is Gillick competence and capacity territory. Genetic results always concern a whole family, so confidentiality is strained too.

How can the NHS justify £1.65 million for one patient?

Casgevy lists at £1,651,000 per patient, though the NHS pays considerably less under a confidential discount, so nobody outside the negotiation knows the real figure.

NICE measures value using the quality-adjusted life year, and since April 2026 the standard threshold has been £25,000 to £35,000 per QALY, up from £20,000 to £30,000.

This is justice, as with weight loss injections, who receives a donated organ and the NHS postcode lottery. The argument the other way is strong: sickle cell disease mostly affects people of African and Caribbean heritage, has long been underfunded, and NICE weighed health inequalities in its decision.

Key Takeaway: The cost argument needs its other half, which is that sickle cell care has been underfunded for decades.

Is gene editing safe?

In body cells it's increasingly safe, and the record so far is reassuring. In embryos it isn't, and the reasons are worth knowing.

• Off-target effects: the guide matches a similar sequence somewhere else in the genome, so the edit lands somewhere other than the intended target.
• Mosaicism: an embryo edited after it's started dividing ends up as a patchwork of edited and unedited cells.
• Damage even on target: a Columbia University team reported in 2020 that cutting precisely on target still left over 90% of the human embryos studied with a lost or damaged chromosome.
• We cannot reliably check: the tests used to inspect an edited embryo aren't reliable, because there's so little DNA to work with.

The case: in late 2018 the Chinese scientist He Jiankui announced twin girls born from embryos he edited, targeting CCR5 for HIV resistance. A third followed in 2019, and he was convicted of illegal medical practice in December 2019.

He also departed from the protective variant that exists in nature, so both twins carry changes never seen in any human being. The consent failures were worse: the parents signed a form calling the study an AIDS vaccine development project, and the named hospital said the signatures appeared forged.

The lesson here is really about oversight rather than about CRISPR. Ethics committees exist to catch the doctor who believes he's making history, as in the Yaser Jabbar case and after Andrew Wakefield.

Key Takeaway: In embryos the problem is measurement as much as risk, and He Jiankui failed on oversight well before he failed on the science.

Is germline gene editing legal in the UK?

No. Creating a baby from an edited embryo is a criminal offence under the Human Fertilisation and Embryology Act 1990, carrying up to ten years in prison. Around 70 countries ban heritable editing, and it remains permitted nowhere.

Research sits under a different rule. Editing embryos in the laboratory is lawful under a licence from the Human Fertilisation and Embryology Authority, provided the embryo is destroyed by 14 days and kept out of the womb.

• The exception that complicates the line: since 2015 the UK has allowed mitochondrial donation, reported as "three-parent babies", to stop mothers passing on mitochondrial disease. In July 2025 Newcastle, the only licensed centre, reported eight babies born this way.
• Why it is contested: the Government argued this falls outside genetic modification because the nucleus is untouched. Mitochondria pass down the female line, so a girl born this way passes donor mitochondria to her own children.

Are designer babies legal in the UK?

No. Editing an embryo and then implanting it to create a baby is a criminal offence here, whatever the reason for doing it. The ban covers editing to prevent serious inherited disease just as much as editing to choose a trait.

Choosing between embryos during IVF is a separate question with its own rules, and it isn't gene editing at all. Our guide to designer babies and embryo screening covers that side.

Key Takeaway: UK law forbids the baby rather than the science, and mitochondrial donation shows that the line is less clean than it first sounds.

What is the difference between treatment and enhancement?

Treatment corrects something that's causing harm, while enhancement improves a trait already working normally, and there's no agreed line anywhere between the two.

The Nuffield Council on Bioethics called the distinction "neither clear nor well understood", and the examples bear that out. Boosting a child’s immunity is prevention and enhancement at the same time, and height has no natural cut-off anywhere along its range.

• The expressivist objection: editing out a trait says something about the people living with it now. The British Deaf Association put it this way in 2024: "Deaf people are not sick or broken. We reject the medical model of deafness that reduces us to our disability."
• The other side: Nuffield found real force in that objection where a disability is mild and socially constructed, much less where the condition seriously shortens a life.

This is where the four pillars stop working as a checklist, because autonomy has nowhere to go when an embryo can't be asked. Max and Keira’s law is the comparison for widening access without coercion.

Key Takeaway: It's perfectly coherent to disvalue a condition while valuing the people who live with it just as much as anyone else.

How can I talk about gene editing in my medicine interview?

Explain the science in one clear sentence and then spend the rest of your answer on the ethics, which is where the marks actually are. You don't need laboratory experience for any of this, so use what you already have.

• A-level biology: you've already met DNA, genes and proteins, so you can explain a guide RNA and an enzyme in your own words.
• Your own experience: meeting someone with a long term condition shows you what repeated admissions cost a family, and an article about Casgevy or an EPQ counts too.

Here's a structure that works for almost any gene editing question:

1. Define it. Say what CRISPR does in one sentence, using the guide and the enzyme.
2. Separate somatic from germline. Make clear which one the question is about before you argue about it.
3. Give both sides. The good Casgevy does, then the safety and consent problems on the germline side.
4. Land a position. Say what you think, in one sentence, without hedging.
5. Say what would change it. Name the evidence or the safeguard that would move you.

Here's what the interviewer is listening for:

• Whether you can define the science accurately: one clear sentence about what CRISPR does matters more than jargon.
• Whether you can hold two sides at once: they want the strongest version of the argument you disagree with.
• Whether you know the UK regulatory position: somatic editing licensed and funded, germline editing a criminal offence, research licensed to 14 days.

Do I need A-level Biology detail to answer a CRISPR question?

No. You need one sentence on what CRISPR does and one on why the somatic and germline distinction matters, and that's genuinely it. A panel is testing your reasoning about the ethics rather than your recall of molecular biology.

This part takes practice rather than reading. In the mock interviews I run, gene editing is the topic where a student most often knows all the facts and still loses the thread halfway through.

Key Takeaway: Say what the technology does in one sentence, then spend everything after that on the ethics.

Example interview questions on gene editing

You are unlikely to be asked any of these word for word, and you do not need a prepared answer to each one. Use them to check your understanding: if you could speak for a minute on most of them, you know this topic well enough for whatever the interviewer actually asks.

Questions to get you thinking

1. What is CRISPR, and should we be using it?
2. What is the difference between somatic and germline gene editing, and why does it matter?
3. Should the NHS spend £1.65 million on one patient when it could treat hundreds?
4. What do you think about the He Jiankui case?
5. A friend says scientists can now design babies. What would you say to them?
6. You are a sixth former on placement and a patient with sickle cell asks if gene therapy would cure her. What do you say?

Harder questions to stretch you

1. Where would you draw the line between treating disease and enhancing a healthy person?
2. Some deaf people argue that editing out deafness devalues deaf lives. How would you answer them?
3. Mitochondrial donation is inherited down the female line. Is that not germline modification already?
4. If germline editing were proved safe tomorrow, what would still stand in the way of legalising it?

Model answer: "Should we edit the genes of embryos to prevent serious inherited disease?"

My honest answer is not yet, and the reason matters more than the verdict.

I would separate the two cases first, because they often get confused. Editing body cells is already happening: Casgevy is a CRISPR treatment for sickle cell disease, on the NHS since January 2025. Editing an embryo is different, because the change passes to that person’s children, and that is the part the law here prohibits.

The case for it is strong. Stopping a devastating inherited condition before a person exists is an enormous good.

Against it, the safety data in embryos is poor, and the tests we use to check an edited embryo are unreliable, so we have no dependable way to measure how badly it has gone.

The person edited is in no position to consent, and their descendants are in the same position. Disabled people also argue, fairly, that editing out a trait says something about people living with it today.

I would add that embryo screening already exists, so the number of families who could only be helped by editing is small.

As a sixth former I am in no position to judge the laboratory data myself. On what I have read my answer is not yet, and what would change it is safety we can verify, a clear unmet need, and a public that has been properly asked.

Why this answer works:

• It split the question: somatic and germline are different arguments, and it said so in the first thirty seconds.
• It used one dated fact: Casgevy on the NHS since January 2025 is specific, checkable and current.
• It was honest about competence: it put the other side at full strength and said what would change its mind.

Several hundred more sit in our interview questions guide and our medicine interview hot topics guide, and we practise answers like this in our medicine interview coaching.

Key Takeaway: Say these out loud and time yourself, because knowing this topic and delivering it in ninety seconds are different skills.

What should I take into the interview room?

Somatic gene editing is already here, licensed and funded, and the arguments about it are cost and safety. Germline editing remains illegal and unresolved, and the arguments there are consent and what we owe to people who don't yet exist.

Related topics: read Charlie Gard, Archie Battersbee and Indi Gregory for parents and doctors disagreeing, and assisted dying for where law and ethics pull apart.

Key Takeaway: If you say nothing else, say that editing body cells and editing embryos are two entirely different debates.