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Glossary

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 gene therapy and are specific to gene therapy treatment options and administration.

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 depend on adenoviruses for replication

Allele
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

Autosomes
any of the numbered chromosomes, not including sex chromosomes2



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 support development of different types of blood cells, such as red blood cells, white blood cells, and platelets6

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 function



CAR T-cell therapy
a treatment where a person's T cells are altered in a lab and then infused back into the person’s body to help attack cancer cells6

CD34
a protein that plays a role in signal transduction and acts as a marker of human stem cells8

Cell
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
diseases in which chromosomes (or parts of chromosomes) are missing or changed11

Chromosome
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
refers to regions within a gene that provide the instructions to produce a protein1, 12

Codon
a sequence of DNA that codes for a specific amino acid2

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

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9
a laboratory tool 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 sequence6



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 life6

DNA (deoxyribonucleic acid)
the substance (or molecule) that carries genetic information in a human cell6

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

Donor
in a hematopoietic stem cell transplant, the person who donates their blood stem cells7



Efficacy
the ability for a medication to achieve its desired effect6 

Electroporation
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 Association (EMA)
the regulatory agency responsible for scientific evaluation of medicine for potential use in the European Union13



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

Gene addition
adds functioning genetic material to do the work of a faulty gene14, 15

Gene editing
the creation of targeted double-stranded breaks in DNA, with or without repair instructions, to disrupt or correct the function of a gene16, 17

Gene expression
when the information encoded in a gene is used and expressed as an effect or trait2,3

Gene inactivation
an approach in gene therapy that turns off or reduces the function of a gene in order to have a therapeutic effect18, 19

Gene insertion
applies genetic material in order to treat a disease at the genetic level20

Gene correction
corrects a faulty gene with functional genetic material with the aim of correcting the faulty gene15

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 RNA21

Genetic material
refers to materials that play a fundamental role in determining the structure and nature of a cell21

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

Genome
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 offspring6

Graft rejection
when donated bone marrow is infused and then rejected by the person receiving the donation21

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



Hemophilia
an inherited disease where blood does not clot properly2

Histone
a protein that provides structural support to a chromosome2



Immunogenicity
the degree to which a substance triggers an immune response21

In vivo
inside the body6



Lentiviral vector
a way to deliver genetic material to a cell using the blueprint of a lentivirus as a guide6

Meganucleases
natural proteins that recognize long DNA sequences. They target a specific site on a gene to make a break22

MegaTALS
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 or dent to transfer their coding sequence to the gene

See glossary for more terms >
22

Mitochondria
membrane-bound cell organelles that produce energy2

Mutation
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 information6

Noncoding DNA
DNA sequences that do not code for amino acids; some noncoding DNA has no known function, while some noncoding DNA plays a role in regulating gene expression2

Non-genetic diseases
diseases that are not attributed to genetics13

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

Nuclease
an enzyme that is capable of cleaving the bond between two bases in a nucleic acid at a specific sequence13

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



Phenotype
observable characteristics or traits (like blood type or eye color) that come from genotype or environment2

Platelet
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

Protein
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



Recessive
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 1 cell to another and causing infection23

Retroviruses
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 proteins13

Self-inactivating lentiviral vector
a vector that, through a process of deleting and manipulating lentiviral components, is no longer able to replicate

Sex chromosomes
a type of chromosome that helps determine the sex2

Short hairpin RNA (shRNA)
an artificial RNA molecule that is used to enable gene supression24

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

Stem cells
cells in the body which can form all the different cell types with specific functions, such as blood cells, brain cells, muscle cells, or bone cells6

Telomere
repetitive sequence of noncoding DNA at the end of a chromosome, which protects the chromosome from damage during cell division2

T-cell
a type of white blood cell that is partly in charge of the body's immune response to pathogens6

Transcription activator-like effector (TALE)
a protein secreted by a bacteria to aid in the infection of plant species. TALEs enable the rapid and systematic targeting of specific DNA sequences. TALEs are used as the basis of transcription activator-like effector nucleases (TALENs), which are used in gene editing25

Transcription activator-like effector-based nucleases (TALEN)
an array of single-protein modules, or nuclease, where each module recognizes a single DNA base pair. These nucleases cleave DNA at a defined distance from TALE recognition sequences. These nucleases are derived from transcription activator-like effectors22

Transgene
a portion of DNA from one organism inserted into the genome of another organism21

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 effective6

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 ones6

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

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

White blood cells
cells the body makes to help fight infections1

Wild-type Virus
is a naturally occurring, non-mutated strain of a virus25

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

References

1. MedicineNet. MedTerms medical dictionary A-Z list. Accessed March 16, 2020. https://www.medicinenet.com/script/main/alphaidx.asp?p=a_dict 2. National Institutes of Health. National Human Genome Research Institute. Talking glossary of genetic terms. Accessed March 16, 2020. https://www.genome.gov/genetics-glossary 3. Stedman’s Medical Dictionary Online. Wolters Kluwer. Accessed March 21, 2020. https://stedmansonline.com/ 4. Mayo Clinic. Bone marrow transplant. Allogeneic stem cell transplant. Accessed March 16, 2020. https://www.mayoclinic.org/tests-procedures/allogeneic-stem-cell-transplant/pyc-20384863 5. Mayo Clinic. Bone marrow transplant. Autologous stem cell transplant. Accessed March 16, 2020. https://www.mayoclinic.org/tests-procedures/autologous-stem-cell-transplant/home/ovc-20384860 6. National Institutes of Health. National Cancer Institute. NCI dictionary of cancer terms. Accessed March 16, 2020. https://www.cancer.gov/publications/dictionaries/cancer-terms 7. Johns Hopkins Medicine. Bone marrow transplantation. Accessed March 16, 2020. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/bone-marrow-transplantation 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 March 16, 2020. https://medlineplus.gov/encyclopedia.html 12. Salzberg SL. Open questions: how many genes do we have? BMC Biol. 2018;16(94). https://doi.org/10.1186/s12915-018-0564-x 13. National Institute of Health. What is DNA? Accessed May 29, 2020. https://ghr.nlm.nih.gov/primer/basics/dna 14. The Free Dictionary. Medical dictionary. Accessed March 16, 2020. https://medical-dictionary.thefreedictionary.com/ 15. FDA Commissioner. What is gene therapy? How does it work? US Food and Drug Administration. Accessed March 1, 2020. https://www.fda.gov/consumers/consumer-updates/what-gene-therapy-how-does-it-work 16. Collins M, Thrasher A. Gene therapy: progress and predictions. Proc Biol Sci. 2015;282(1821): 20143003. 17. 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. 18. 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. 19. National Institute of Health. Gene expression. Accessed May 29, 2020. https://www.genome.gov/genetics-glossary/Gene-Expression 20. Cambridge Dictionary. Accessed March 16, 2020. https://dictionary.cambridge.org/ 21. El-Brolosy MA, Stainier DYR. Genetic compensation: A phenomenon in search of mechanisms. PLoS Genet. 2017;13(7):e1006780. 22. Papapetrou EP, Schambach A. Gene insertion into genomic safe harbors for human gene therapy. Mol Ther. 2016;24(4):678-684. 23. BiologyOnline. Learn biology online. Accessed March 16, 2020. https://www.biologyonline.com 24. 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. 25. Aidsinfo. Wild type virus. Accessed June 11, 2020. https://aidsinfo.nih.gov/understanding-hiv-aids/glossary/753/wild-type-virus 

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