Reference
Glossary
94 terms used across The CRISPR Atlas, each defined in plain language. Technical terms throughout the site link back here.
94 terms shown
A
One of the four DNA letters, written A. It pairs with thymine.
A small virus, harmless in itself, widely modified into a delivery vehicle for genetic medicines. Usually abbreviated AAV. Its cargo limit of about 4.7 kilobases is a major constraint.
One of the alternative versions of a gene at a given location. You inherit one from each parent.
Coming from a donor rather than the patient. Allogeneic cell therapies are made in advance and given off the shelf, which requires gene editing to stop the donor cells attacking the recipient.
One of the building blocks that proteins are made from. Each set of three DNA letters specifies one amino acid.
A procedure that separates and collects specific cells from a person's blood, returning the rest. It is how stem cells are collected for editing.
Coming from the patient's own body. Autologous cell therapies are manufactured individually for each person.
B
Changing one DNA letter into another chemically, without cutting both strands of the helix.
Two DNA letters bonded across the double helix: A with T, or G with C. Genome sizes are measured in base pairs.
Biologics licence application — the submission a company makes to the FDA seeking approval to market a biological medicine.
The most serious warning a medicines regulator can require on a product label, reserved for risks prescribers must be explicitly told about.
An unintended change to a second editable letter that happens to sit inside a base editor's small working window, next to the one you meant to change.
C
Clustered Regularly Interspaced Short Palindromic Repeats — a bacterial immune system reprogrammed into a tool for finding and changing chosen DNA.
The stretch of a bacterial genome where fragments of past viral invaders are stored between repeated sequences — the original biological CRISPR.
Using a disabled CRISPR protein to increase a gene's expression, without changing its sequence.
Using a disabled CRISPR protein to block a gene from being read, without changing its sequence.
A family of CRISPR proteins that cut DNA leaving staggered ends and recognise a different sequence signal from Cas9. Also used in diagnostics.
A CRISPR protein that targets RNA rather than DNA, so its effect is temporary and the genome is untouched.
The best-known CRISPR protein. Guided by an RNA, it cuts both strands of DNA at a chosen site.
DNA together with the proteins it is packaged with. How tightly it is packed affects whether a gene can be read at all.
One long DNA molecule packaged with proteins. Humans normally have 46, in 23 pairs.
An order from a regulator suspending or restricting a clinical trial, usually after a safety concern. Holds can be lifted once the concern is addressed.
The habit some CRISPR proteins have of cutting nearby genetic material indiscriminately once activated. A problem inside cells and the basis of CRISPR diagnostics.
Chemotherapy or antibody treatment given before a cell therapy to clear space in the bone marrow so edited cells can engraft. It is the source of most of the risk in ex vivo therapies.
One of the four DNA letters, written C. It pairs with guanine.
D
Deoxyribonucleic acid — the molecule that stores genetic instructions, written in an alphabet of four letters.
The loss of one or more DNA letters. If the number lost is not a multiple of three it shifts the reading frame and usually destroys the protein.
An inheritance pattern in which one faulty copy of a gene is enough to cause the condition.
A cut through both strands of the DNA helix. Ordinary CRISPR makes these deliberately; base and prime editing were invented to avoid them.
E
The small stretch of DNA, usually four or five letters, within which a base editor can act. Anything editable inside it may be changed.
When transplanted cells take hold in the body and begin producing new cells. The first milestone after any cell therapy.
A stretch of DNA that increases how strongly a gene is expressed, often from a distance. The approved sickle cell therapy targets an enhancer, not a gene.
Deliberately writing or erasing those marks at a chosen gene, to change its expression without altering sequence.
Chemical marks on DNA and its packaging proteins that change how genes are read without changing the sequence itself. Cells copy these marks when they divide.
Editing performed on cells outside the body, which are then returned to the patient.
A part of a gene retained in the final message and usually translated into protein.
F
The form of haemoglobin made before birth. It does not sickle, which is why switching it back on treats sickle cell disease.
A shift in how DNA is read in groups of three, caused by inserting or deleting a number of letters not divisible by three. It usually destroys the protein.
G
A stretch of DNA carrying the instructions for one product, usually a protein.
An engineered genetic element designed to spread through a wild population far faster than normal inheritance would allow.
Changing DNA that is already present in a cell, at a chosen location.
Treating disease by delivering genetic material. In its classic form it adds a working copy of a gene rather than changing the existing one.
The complete set of genetic material in an organism.
The genetic makeup of an individual, as distinct from the observable characteristics it produces.
Cells that can pass genetic information to children — eggs, sperm and embryos. Editing them would be heritable, and is prohibited or unapproved for clinical use in most countries.
Good manufacturing practice — the quality standard cell and gene therapy products must be made under.
One of the four DNA letters, written G. It pairs with cytosine.
The short RNA molecule that tells a CRISPR protein where to act. Changing it is how the system is reprogrammed.
H
When one working copy of a gene is not enough for normal function — a situation better suited to turning expression up than to correcting sequence.
Homology-directed repair — the precise repair pathway that can copy a supplied template into a break. It works only in dividing cells and is inefficient.
Engineered to avoid recognition by the immune system, so that transplanted cells can survive without immunosuppressive drugs.
I
Editing performed inside the body, usually by infusion or injection, rather than on cells outside it.
A small insertion or deletion, the usual result of a cell repairing a CRISPR cut by end joining.
The addition of one or more DNA letters into a sequence.
Harm caused when inserted genetic material lands inside or beside an important gene and disrupts it.
A part of a gene removed from the message before the protein is made. Faults in introns can still cause disease by disrupting how the message is assembled.
K
Reducing the amount of a gene's product without eliminating it, usually temporarily.
Disabling a gene so it no longer produces a working product. The most reliable thing gene editing does.
L
A microscopic fat bubble carrying genetic cargo into cells. The delivery technology behind in vivo CRISPR and mRNA vaccines; it goes efficiently to the liver.
M
A change of one DNA letter that alters which amino acid is used, giving a protein that is present but altered.
When some cells in an organism carry a change and others do not. It is a serious problem in embryo editing, where it means the result cannot be controlled or fully known.
Making several edits in the same cell at once. Necessary for off-the-shelf cell therapy, and riskier than a single edit.
A change in DNA sequence. Most have no effect; a minority cause disease.
N
A modified Cas protein that cuts only one strand of DNA. Used in base and prime editors to avoid a full break.
Non-homologous end joining — the fast, always-available, error-prone repair pathway that usually seals a CRISPR cut and disables the gene.
A change that creates a premature stop signal, ending a protein early and usually destroying its function.
One unit of DNA or RNA: a sugar, a phosphate and one of the four bases. The letters of the genetic alphabet.
O
An edit made somewhere other than the intended site, because the guide tolerated a mismatch. Measured empirically, not assumed absent.
A regulatory status for treatments aimed at rare diseases, carrying incentives intended to make small-population development viable.
P
Protospacer-adjacent motif — a short sequence that must sit next to the target or Cas9 will not cut. It is a real constraint on where you can edit.
The observable characteristics of an organism, resulting from its genes and its environment.
A change affecting a single DNA letter. The most common kind of disease-causing variant, and the reason base editing was invented.
Writing a chosen new stretch of DNA sequence into a specific site, without cutting both strands and without a separate donor template.
The stretch of DNA where the machinery that reads a gene first binds. Its accessibility largely determines whether the gene is expressed.
The molecular machines that do most of the work in cells. Genes are the instructions for making them.
R
Ribonucleic acid — the single-stranded working copy a cell makes when it needs to use a gene.
RNA interference — using short RNA molecules to have the cell destroy a specific message, lowering a protein's level temporarily.
An inheritance pattern in which both copies of a gene must be faulty for the condition to appear.
An enzyme that cuts and rejoins DNA at specific recognition sites, able to insert large sequences.
The editing protein and its guide RNA delivered together as a ready-made complex. It acts quickly and then degrades, which limits off-target opportunity.
S
Affecting the body's ordinary cells rather than eggs, sperm or embryos. Somatic changes are not inherited, and all approved gene editing is somatic.
Removing introns and joining exons to make the final message. Many disease-causing variants act by disrupting it.
A measurement used as a stand-in for the outcome that actually matters — a blood marker rather than survival. It may or may not predict real benefit.
T
Transcription activator-like effector nuclease — an earlier editing tool built from protein modules, each recognising one DNA letter.
One of the four DNA letters, written T. It pairs with adenine.
A gene deliberately introduced into an organism, as distinct from one that was already there.
An enzyme that moves a segment of DNA from one place in the genome to another.
V
Variant of uncertain significance — a genetic change that has been found but whose effect, if any, is not known.
Anything used to carry genetic material into cells — a modified virus, a lipid nanoparticle, or a piece of engineered DNA.
W
The typical, unaltered version of a gene or organism, used as the reference for comparison.
Z
The first programmable gene-editing tool used in people, built from small protein modules that each grip about three DNA letters.
D
A version of Cas9 that can still find its target but cannot cut. It is the foundation of base editors, prime editors and gene-regulation tools.
P
The guide used in prime editing, which carries both the target address and the replacement sequence to be written.
T
A small RNA discovered by Emmanuelle Charpentier that is required for CRISPR-Cas9 to function; fused with the targeting RNA it forms the single guide RNA.