Like any specialized discipline, the fields of genetics and gene therapy have their own vocabulary. The terms defined on this page have been collected throughout genehome to help you understand these subjects as you read about them.
The following terms have been defined within the context of genetics and our current knowledge of gene therapy.

Acquired mutation
a genetic change that happens after conception; this change is passed on to cells that come from the cell that acquires the change1

Adeno-associated virus
a single-stranded DNA virus that depends on adenoviruses for replication

any variant of a gene that can be found in the same place on a specific chromosome2,3

Allogenic hematopoietic stem cell transplant (allogenic HSCT or allo HSCT)
a transplant in which the person receives blood stem cells or bone marrow cells from another person (a donor)4

Amino acids
a set of 20 different molecules used to build proteins2

Autologous hematopoietic stem cell transplant (autologous HSCT or auto HSCT)
a transplant in which the patient receives their own blood stem cells or bone marrow that was previously collected5

any of the numbered chromosomes, not including sex chromosomes2

Base editing
a gene editing method to edit select bases without cleaving DNA6

Base pairs
2 complementary DNA bases that are bonded together forming one step on the DNA ladder2

Blood stem cells
cells found in the bone marrow and circulating blood that develop into different types of blood cells, such as red blood cells, white blood cells, and platelets7

Bone marrow transplant (BMT)
the process of infusing blood stem cells from another person (a donor) into a person who has a genetic disease or whose bone marrow or immune system is compromised to help correct or restore normal cell function8

CAR T-cell therapy
a treatment where a person's T cells (a part of the immune system) are genetically modified to recognize and attack cancer cells7

a protein that plays a role in signal transduction and acts as a marker of human stem cells8

the basic building block of living things; they are enclosed by a wall or membrane and have structures inside them that perform a variety of functions that help them, and/or the organism they are part of, to survive2

Chemical disruption vector
a type of vector that is typically designed to target specific cells and increase the delivery of genetic material to cytosol or nucleus9, 10

Chromosomal disease
a disease in which chromosomes (or parts of chromosomes) are missing or changed11

an organized structure of DNA found in the nucleus of the cell. Humans have 23 pairs of chromosomes, and they receive half from their mother and half from their father2

Clinical trial
a study that measures the safety and effectiveness of a medication in humans1

Coding DNA
regions within a gene that provide the instructions to produce a protein1, 12

a sequence of DNA that codes for a specific amino acid2

Complex genetic diseases
diseases in which changes occur in two or more genes11

the process where a patient is prepared to receive transplanted donor cells through chemotherapy, radiotherapy, and/or immunotherapy.13

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9
a gene editing technique that uses a specially designed RNA molecule to guide a Cas9 enzyme to a specific sequence of DNA so it can change or edit that site sequence7

De novo
genetic mutation: a genetic mutation/alteration that appears for the first time in a family as a result of a variant in an egg or sperm cell of the parents, or a variant that occurs in the fertilized egg itself; this genetic mutation is not present in either parent, only the offspring; it may also occur later in life7

DNA (deoxyribonucleic acid)
the hereditary material in humans and almost all other organisms14

Dominant trait
a genetic trait that appears when there is only one copy of that gene1

in a hematopoietic stem cell transplant, the person who donates their blood stem cells15

the ability of a medication to achieve its desired effect7

the use of an electric field to make a cell more permeable, which allows the delivery of genetic material9

Ex vivo
outside the body6

European Medicines Agency (EMA)
the regulatory agency responsible for scientific evaluation of medicine for potential use in the European Union16

instructions made of DNA used to create the proteins the body needs to function6

Gene addition
a technique that adds functioning genetic material to do the work of a faulty gene17,18

Gene editing
the creation of targeted double-stranded breaks in DNA, with or without repair instructions, to disrupt or correct the function of a gene19,20

Gene expression
the information encoded in a gene is used to direct the assembly of a protein molecule21

Gene inactivation
an approach in gene therapy that turns off or reduces the function of a gene in order to have a therapeutic effect20,22

Gene insertion
a technique that applies genetic material in order to treat a disease at the genetic level23

Gene correction
a technique that corrects a faulty gene with functional genetic material with the aim of correcting the faulty gene17

Genetic disease
a disease caused by a mutation (or problem) in one or more genes1,3

Genetic information
the hereditary information coded in a person’s DNA or RNA24

Genetic material
refers to DNA or RNA that play a fundamental role in creating proteins critical to a cell’s structure or its function in the body24

Gene therapy
a method of treating genetic diseases at the genetic level (the source) with the goal of changing the course of a disease2 

the entire set of genetic instructions found in a cell nucleus2

Gene mutation
a change in DNA sequence2

Germline mutation
a gene change in a body's reproductive cell that is incorporated into the DNA of a person’s offspring7

Graft rejection
a situation that occurs when donated bone marrow is infused and then rejected by the person receiving the donation24

Graft-versus-host disease
an adverse reaction to a bone marrow transplant in which the body attacks its own cells1 

an inherited disease where blood does not clot properly2

a protein that provides structural support to a chromosome2

the degree to which a substance triggers an immune response23

In vivo
inside the body7

the process where genetic material moves into the nucleus of a cell and integrates with the host genome, allowing for stable expression25

Lentiviral vector
a way to deliver genetic material to a cell using the blueprint of a lentivirus as a guide7

natural proteins that recognize long DNA sequences. They target a specific site on a gene to make a break24

artificial nucleases composed of an array of transcription activator-like effector (TALE) DNA-binding domains and a Meganucleasesnatural proteins that recognize long DNA sequences. They target a specific site on a gene to make a break

See glossary for more terms >

membrane-bound cell organelles that produce energy2

a change in a DNA sequence2

(US) National Institutes of Health
a federal agency in the US that conducts biomedical research in its own laboratories; supports the research of non-federal scientists in universities, medical schools, hospitals, and research institutions throughout the country and abroad; helps in the training of research investigators; and fosters communication of medical information7

Non-coding DNA
DNA sequences that do not code for amino acids; some non-coding DNA has no known function, while other non-coding DNA plays a role in regulating gene expression2

Non-genetic diseases
diseases that are not attributed to genetics14

the process where genetic material does not integrate with the host genome and thus has transient expression25

Non-viral vector
a way to deliver genetic material to a cell that is not based on a virus9

an enzyme that is capable of cleaving the bond between two bases in a nucleic acid at a specific sequence14

a membrane-bound organelle that contains the cell’s chromosomes2

observable characteristics or traits (like blood type or eye color) that come from genetic traits and/or environmental effects2

an element in the blood that assists in clotting1

Polymer-based vector
polymers are one of the substances used to create chemical vectors. These complexes protect DNA and facilitate cell uptake and intracellular delivery9

Preclinical study
a study that aims to demonstrate proof of concept, support efficacy, and/or measure safety of a treatment or therapy before it is allowed to be tested in people1

class of molecules composed of one or more chains of amino acids that perform different functions the body needs including structure, function, and regulation of tissues and organs2

a trait that appears only when a person has two copies of a gene1

Red blood cells
the blood cells that carry oxygen1

Replication incompetent
in reference to viruses used for vectors that are incapable of self-replication and therefore incapable of spreading from one cell to another and causing infection26

a virus that uses RNA as its genetic material; when a retrovirus infects a host cell, the RNA is converted into DNA, which then incorporates into the genome of the host cell2

Ribonucleic acid (RNA)
a nucleic acid that is present in all human cells. It is the product of transcription and acts as an intermediary between DNA and proteins14

Sex chromosomes
a type of chromosome that helps determine a person's sex2

Short hairpin RNA (shRNA)
an artificial RNA molecule that is used to enable gene supression27

Single-gene diseases
types of diseases, also called monogenic diseases, in which a mutation is present in one gene only11

Stem cells
cells in the body that have the unique potential to develop into all the different cell types with specific functions, such as blood cells, brain cells, muscle cells, or bone cells7

repetitive sequence of non-coding DNA at the end of a chromosome, which protects the chromosome from damage during cell division2

a type of white blood cell that is partly in charge of the body's immune response to pathogens7

Transcription activator-like effector-based nucleases (TALEN)
arrays of single-protein modules, or nucleases, where each module recognizes a single DNA base pair. These nucleases cleave DNA at a defined distance from TALEN recognition sequences. These nucleases are derived from transcription activator-like effectors24

a portion of DNA from one organism inserted into the genome of another organism23

US Food and Drug Administration (FDA)
an agency in the US federal government whose mission is to protect public health by making sure that drugs, medical devices, and other equipment are safe and effective7

Viral vector
a way to deliver genetic material to a cell using the blueprint of a virus as a guide; it may be used to carry genes and change mutated cells to healthy ones7

an infectious agent smaller than a bacteria consisting of a small RNA or DNA genome surrounded by a protein coat2

a delivery system used to introduce genetic material into the cell nucleus2

White blood cells
cells the body makes to help fight infections1

Wild-type virus
a naturally occurring, non-mutated strain of a virus28

Zinc finger nucleases (ZFN)
artificial restriction enzymes generated by fusing a zinc finger DNA-binding domain to a DNA-cleavage domain; ZFNs are used in gene editing applications13


1. MedicineNet. MedTerms medical dictionary A-Z list. Accessed July 1, 2021. 2. National Institutes of Health. National Human Genome Research Institute. Talking glossary of genetic terms. Accessed July 1, 2021. 3. Stedman’s Medical Dictionary Online. Wolters Kluwer. Accessed July 1, 2021. 4. Mayo Clinic. Bone marrow transplant. Allogeneic stem cell transplant. Accessed July 1, 2021. 5. Mayo Clinic. Bone marrow transplant. Autologous stem cell transplant. Accessed July 1, 2021. 6. Rees H, Liu D. Base editing: precision chemistry on the genome and transcriptome of living cells. Nat Rev Genet. 2018;19(12):770-788. 7. National Institutes of Health. National Cancer Institute. NCI dictionary of cancer terms. Accessed July 1, 2021. 8. Sidney LE, Branch MJ, Dunphy SE, Dua HS, Hopkinson A. Concise review: evidence for CD34 as a common marker for diverse progenitors. Stem Cells. 2014:23(6):1380-1389. 9. Al-Dosari MS. Gao X. Nonviral gene delivery: principle, limitations, and recent progress. AAPS J. 2009;11(4);671-681. 10. Wang D, Gao G. State-of-the-art human gene therapy: part I. Gene delivery technologies. Discov Med. 2014;18(97):67-77. 11. National Institutes of Health. Medline Plus. Medical encyclopedia. Accessed July 1, 2021. 12. Salzberg SL. Open questions: how many genes do we have? BMC Biol. 2018;16(94). 13. Zulu S, Kenyon M. Principles of conditioning therapy and cell infusion. In Kenyon M, Babic A, eds. The European Blood and Marrow Transplantation Textbook for Nurses. Springer International Publishing. 2018:89-96. 14. National Institutes of Health. Help me understand genetics. Accessed July 1, 2021. 15. Johns Hopkins Medicine. Bone marrow transplantation. Accessed July 1, 2021. 16. The Free Dictionary. Medical dictionary. Accessed July 1, 2021. 17. FDA Commissioner. What is gene therapy? How does it work? US Food and Drug Administration. Accessed July 1, 2021. 18. Collins M, Thrasher A. Gene therapy: progress and predictions. Proc Biol Sci. 2015;282(1821): 20143003. 19. Guha TK, Wai A, Hausner G. Programmable genome editing tools and their regulation for efficient genome engineering. Comput Struct Biotechnol J. 2017;15:146-160. 20. Yanik M, Müller B, Song F, et al. In vivo genome editing as a potential treatment strategy for inherited retinal dystrophies. Prog Retin Eye Res. 2017;56:1-18. 21. National Institutes of Health. Gene expression. Accessed July 1, 2021. 22. Cambridge Dictionary. Accessed July 1, 2021. 23. El-Brolosy MA, Stainier DYR. Genetic compensation: A phenomenon in search of mechanisms. PLoS Genet. 2017;13(7):e1006780. 24. Papapetrou EP, Schambach A. Gene insertion into genomic safe harbors for human gene therapy. Mol Ther. 2016;24(4):678-684. 25. Nowakowski A, Andrzejewska A, Janowski M, Walczak P, Lukomska B. Genetic engineering of stem cells for enhanced therapy. Acta Neurobiol Exp. 2013;73:1-18. 26. Biology Online. Dictionary. Accessed July 1, 2021. 27. Corrigan-Curay J, O’Reilly M, Kohn D, et al. Genome editing technologies: defining a path to clinic. Mol Ther. 2015;23(5):796-806. 28. Clinical Info. Wild type virus. Accessed July 1, 2021.

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