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, which is called somatic editing, but bans editing embryos, eggs or sperm to make a baby, because those changes would pass to every future generation. Casgevy, a CRISPR therapy for sickle cell disease, has been available on the NHS since January 2025.

I am Dr Akash Gandhi, an NHS GP preparing applicants for medical school interviews at TheUKCATPeople since 2012. The surprise with gene editing is that it has already arrived. A CRISPR therapy is licensed here and funded by the NHS, so this is a live topic rather than a futuristic one.

Most of the argument is in the ethics rather than the biology, which is where a panel will want to take the conversation. Our guide to answering medical ethics interview questions has the framework; below is the content.

What is CRISPR, in plain English?

CRISPR finds one sequence in a genome and changes it. It has two parts: a guide RNA matching the target, and an enzyme, usually Cas9, that cuts where the guide lands. The guide is the satnav, the enzyme the scissors. Charpentier and Doudna won the 2020 Nobel Prize in Chemistry for it.

Key Takeaway: CRISPR cuts, it does not repair. The cell patches the break, and that is where unpredictability starts.

Is gene editing the same as gene therapy?

No. Only the first row below is gene editing, and the three are easy to mix up, so it is worth keeping them separate.

Asked to name a gene editing therapy on the NHS, say Casgevy. Calling CAR-T "gene editing" is the usual slip: it adds a gene rather than editing one the patient already has.

Key Takeaway: Casgevy edits. Zolgensma and CAR-T add, and neither rewrites the patient’s own faulty sequence.

What is the difference between somatic and germline editing?

Somatic editing changes DNA in body cells, so it affects only that patient. Germline editing changes eggs, sperm or an embryo, so the change appears in every cell and passes to that person’s children.

Key Takeaway: Say somatic or germline early, because germline editing raises a question medicine rarely faces: what you owe someone not yet born.

Is gene editing already 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 only to people with severe repeated crises and no matching marrow donor.

It does not fix the sickle gene at all. It works around it, and this is the mechanism worth remembering.

• The starting point. We are all born making fetal haemoglobin, which does not 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.

Why "cure" is the wrong word

First comes chemotherapy to clear the marrow, then four to six weeks in hospital, and it carries a serious risk of infertility. A 12-year-old may be offered an end to a lifetime of crises at the price of never having biological children.

Beneficence says take the crises away. Non-maleficence points at the possibility of sterilising a child. Autonomy is the difficult one, because a 12-year-old cannot simply be asked, which puts this in Gillick competence and capacity territory. Genetic results are never about one person, so confidentiality is strained too.

Key Takeaway: Asked what is difficult about gene therapy, the price is not the most interesting answer. It may cost a 12-year-old their fertility.

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

Casgevy lists at £1,651,000 per patient. The NHS pays less under a confidential discount, so nobody outside the negotiation can check what it actually pays.

NICE judges 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. A lot of prep material still quotes the older figure.

This is justice in its purest form, as with weight loss injections and who receives a donated organ.

There is a strong argument the other way. Sickle cell disease mostly affects people of African and Caribbean heritage, has long been underfunded, and NICE weighed health inequalities in its decision. See also the NHS postcode lottery.

Key Takeaway: The cost argument needs its other half: sickle cell care has long been underfunded.

Can we do it safely?

In body cells, increasingly yes. In embryos, no.

• Off-target effects and mosaicism. Edits in the wrong place, because the guide matched a similar sequence elsewhere; or an embryo edited after it starts dividing, leaving 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 are themselves unreliable, because there is so little DNA. Not being able to measure the damage is the argument against doing it in patients.
• The asymmetry. If somatic editing goes wrong, one consenting patient is harmed and it stops there. Germline harm lands on someone who never consented and cannot be recalled.

Key Takeaway: On embryos, we cannot yet tell whether an edit has gone well, which is more precise than calling it unsafe.

What happened with He Jiankui and the CRISPR babies?

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

The detail that usually gets left out is that he did not reproduce the protective variant that exists in nature. One twin has a completely unedited copy, and both carry changes never seen in any human. He knew this before implantation. The consent failures were worse than the science.

• The paperwork was false. What the parents signed called the study an "AIDS vaccine development project", which it was not, and the hospital named on the ethics approval said no meeting happened and the signatures appeared forged.
• Nobody has checked on the children. There has been no independent follow-up, so asked whether they are healthy, the honest answer is that nobody knows.

The lesson is oversight, not CRISPR. Ethics committees and scrutiny catch the doctor who believes he is making history, as in the Yaser Jabbar case and after Andrew Wakefield.

Key Takeaway: The scandal was not the CRISPR. It was bypassing the safeguards that make human research legitimate.

Where does UK law stand on gene editing?

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. The answer to "is it allowed here?" is no. Around 70 countries ban heritable editing, and none permits it.

Research is different, and this is the part that often gets lost. 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 never implanted.

• 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. Newcastle is the only licensed centre, and in July 2025 the team there reported eight babies born this way.
• Why it is contested. The Government argued it is not genetic modification because the nucleus is untouched. But mitochondria pass down the female line, so a girl born this way passes donor mitochondria to her children. It is heritable, so Britain has arguably crossed the line it says it will not cross.

Key Takeaway: UK law forbids the baby, not the science, and mitochondrial donation shows the line is less clean than it sounds.

Where is the line between treatment and enhancement?

The usual line is that curing disease is fine and improving healthy traits is not. It does not survive much pressure.

The Nuffield Council on Bioethics called the distinction "neither clear nor well understood". Boosting a child’s immunity is prevention and enhancement at once, and height has no natural cut-off.

• The expressivist objection. Editing out a trait sends a message about people living with it now. Disabled people make this argument more forcefully than philosophers do.
• Said plainly. 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 did not accept it wholesale, finding real force where a disability is mild and socially constructed, much less where the condition seriously shortens a life.

Key Takeaway: It is coherent to disvalue a condition while valuing equally the people who have it, and that is worth saying out loud.

How do the four pillars apply to a gene editing station?

Gene editing is where the four pillars stop being a checklist, because on the germline side one breaks.

• Beneficence. An end to a lifetime of sickle cell crises, or a child with spinal muscular atrophy who sits and walks.
• Non-maleficence. Off-target damage, the fertility risk, and inherited harm. Not "is it safe" but "safe enough compared to what".
• Autonomy. The one that breaks: an edited embryo cannot be asked, and unlike ordinary parental consent it binds grandchildren too.
• Justice. Who gets a £1.65 million treatment, and what stops to pay for it? Max and Keira’s law is the comparison for widening access without coercion.

Have Charlie Gard, Archie Battersbee and Indi Gregory ready for parents and doctors disagreeing, and assisted dying for where law and ethics diverge. In the mock interviews I run, this is the section that takes the most practice.

Key Takeaway: Name the pillar that breaks rather than listing four. On germline editing it is autonomy that cannot be satisfied.

What interview questions could come up on this?

Likely questions

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 disease asks if gene therapy would cure her. What do you say?

Less likely questions (harder, but worth knowing)

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 I think the reason matters more than the verdict.

I would separate two things, because they 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 ends up in every cell and passes to that person’s children, which is what is illegal here.

The case for it is strong. Stopping a devastating inherited condition before a person exists is an enormous good, and I would not dismiss a family who wanted it.

Against it, three things. The safety data in embryos is poor, and worse, the tests we use to check an edited embryo are unreliable, so we cannot measure how badly it has gone.

The person edited cannot consent, and nor can their descendants. And disabled people argue, fairly, that editing out a trait says something about people living with it today.

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

So, not yet. What would change my mind is safety we can verify, a clear unmet need, and a public that has been asked.

Why this answer works:

• It split the question. Somatic and germline are different arguments, and the answer 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 landed a position and said what would change it. It also gave the case for editing at its strongest, named the disability objection, and finished on a point that is easy to overlook: screening already covers nearly all the need.

Several hundred more sit in our medical school interview questions guide and our medicine interview hot topics guide; our medicine interview tutoring runs mock MMI and panel interviews.

Key Takeaway: These are worth saying out loud and timing. Knowing this topic and delivering it in ninety seconds are different skills.

The one-line summary to take into the room

Somatic gene editing is here, licensed and funded; the arguments are cost and safety. Germline editing is illegal and unresolved; the arguments are consent and what we owe people not yet born.