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Glossary of Gene Therapy Terms

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AAV (adeno-associated virus): A viral vector system for gene delivery.
Acquired mutations: Gene changes that arise within individual cells and accumulate throughout a person's lifetime; also called somatic mutations.
Adenosine deaminase deficiency (ADA): A severe immunodeficiency disease that results from a lack of the enzyme adenosine deaminase. It usually leads to death within the first few months of life.
Adenovirus: A group of DNA containing viruses which cause respiratory disease, including one form of the common cold. Adenoviruses used in gene therapy are altered to carry a specific tumor-fighting gene or can be used to treat cystic fibrosis and potentially other diseases.
Alleles: Variant forms of the same gene. Different alleles produce variations in inherited characteristics such as eye color or blood type.
Alphavirus: A genus of viruses of the family Togaviridae, including Sindbis Virus and Semliki Forest Virus, that cause encephalitis or febrile illness with rash or arthralgia.
Alzheimer's disease: A disease that causes memory loss, personality changes, dementia and, ultimately, death. Not all cases are inherited, but genes have been found for familial forms of Alzheimer's disease.
Amino acid: Any of a class of 20 molecules that combine to form proteins in living things.
Amyotrophic lateral sclerosis: An inherited, fatal degenerative nerve disorder; also known as Lou Gehrig's disease.
Anti-angiogenesis: Prevents the growth of new blood vessels. Tumors need their own blood supply to survive and by halting the development of new blood vessels, the tumor's supply of oxygen and nutrients are cut off, thus destroying the tumor.
Antigens: A substance that when introduced into the body stimulates the production of an antibody. Antigens include toxins, bacteria, foreign blood cells, and the cells of transplanted organs.
Apoptosis: Programmed cell death, the body's normal method of disposing of damaged, unwanted, or unneeded cells.
Autosome: Any of the non-sex-determining chromosomes. Human cells have 22 pairs of autosomes.

Base pairs: The two complementary, nitrogen-rich molecules held together by weak chemical bonds. Two strands of DNA are held together in the shape of a double helix by the bonds between their base pairs.
Biologics: A classification of products derived from living sources, such as humans, animals, bacteria and viruses. Vaccines, immune globulin, and anti-toxins are biologics.
BRCA1 breast cancer susceptibility gene: A mutated version of BRCA1 (a gene that normally helps to restrain cell growth), which predisposes a person toward developing breast cancer.
Carrier: A person who has a recessive mutated gene, together with its normal allele. Carriers do not usually develop disease but can pass the mutated gene on to their children.
Cell: Small, watery, membrane-bound compartment filled with chemicals; the basic subunit of any living thing.
Chemical base: An essential building block. DNA contains four complementary bases: adenine, which pairs with thymine, and cytosine, which pairs with guanine. In RNA, thymine is replaced by uracil.
Chromosomes: Long strings of genetic material made up of DNA and accessory proteins. The DNA contains the approximately 30,000 to 100,000 genes that make up the human genome. Chromosomes come in pairs, and a normal human cell contains 46 chromosomes, 22 pairs of autosomes and two sex chromosomes.
Clinical Translation: Process that transforms research evidence into clinical guidelines and policy. The aim of translation is to provide useful, useable, and relevant packages of summarized evidence to clinicians in a form that suits their time, cost, and care standards. Generically, these evidence-based clinical packages are called clinical practice guidelines.
Clinical Trial: A clinical trial is a research study in human volunteers to answer specific questions about vaccines or new therapies or new ways of using known treatments. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are the fastest and safest way to find treatments that work in people. Trials are in four phases: Phase I tests a new drug or treatment in a small group; Phase II expands the study to a larger group of people; Phase III expands the study to an even larger group of people; and Phase IV takes place after the drug or treatment has been licensed and marketed.
Clone: A group of identical genes, cells, or organisms derived from a single ancestor.
Cloning: The process of making genetically identical copies.
Cystic fibrosis: An inherited disease in which a thick mucus clogs the lungs and blocks the ducts of the pancreas.
Cytoplasm: The cellular substance outside the nucleus in which the cell's organelles are suspended.
DNA (deoxyribonucleic acid): Genes are composed of segments of DNA, a very long molecule that carries a cell's genetic information. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The sequence of nucleotides determines individual hereditary characteristics.
DNA repair genes: certain genes that are part of a DNA repair pathway; when altered, they permit mutations to pile up throughout the DNA.
DNA sequencing: Determining the exact order of the base pairs in a segment of DNA.
Dominant allele: A gene that is expressed, regardless of whether its counterpart allele on the other chromosome is dominant or recessive. Autosomal dominant disorders are produced by a single mutated dominant allele, even though its corresponding allele is normal.
Duchenne muscular dystrophy: A form of muscular dystrophy that is characterized by decreasing muscle mass and progressive loss of muscle function in male children. This disorder is caused by a mutation in a specific gene within the X chromosome that provides instructions for the formation of the dystrophin protein. Females can be carriers but generally do not experience the symptoms of the condition.
Enzyme: A protein that facilitates a specific chemical reaction.
Ex vivo Gene Therapy : Patient cells are harvested and cultivated in the laboratory and incubated with vectors carrying a corrective or therapeutic gene. Cells with the new genetic information are then harvested and transplanted back into the patient from whom they were derived.
Familial cancer: Cancer, or a predisposition toward cancer, that runs in families.
Fanconi anemia: A genetic disease that causes cells in the bone marrow to die.
Functional gene tests: Biochemical assays for a specific protein, which indicates that a specific gene is not merely present but active.
Gaucher's disease: A genetic disease that affects fat metabolism.
Gene: A segment of DNA found on a chromosome that codes for a particular protein. Humans have approximately 20,000 to 25,000 genes contains the code for a specific product, typically, a protein such as an enzyme.
Gene deletion: The total loss or absence of a gene.
Gene doping: The non-therapeutic use of cells, genes, genetic elements, or of the modulation of gene expression, having the capacity to improve athletic performance.
Gene expression: The process by which a gene's coded information is translated into the structures present and operating in the cell (either proteins or RNAs).
Gene mapping: Determining the relative positions of genes on a chromosome and the distance between them.
Gene markers: Landmarks for a target gene, either detectable traits that are inherited along with the gene, or distinctive segments of DNA.
Gene testing: Examining a sample of blood or other body fluid or tissue for biochemical, chromosomal, or genetic markers that indicate the presence or absence of genetic disease.
Gene Therapy: Treatment that consists of introducing into a patient a normal copy of one or more defective genes responsible for the patient’s disease. When a gene is damaged, the blueprint for the construction of the protein it codes for is imperfect: the resulting protein is therefore abnormal. The goal of gene therapy is to cure a genetic disease by repairing the damaged gene responsible for the disease. It involves introducing a normal copy of the gene into cells containing the damaged version. The cells then can produce the normal protein.
Genetic Engineering: A way of directly manipulating genetic material in a cell or organism to produce desired traits.
Genetics: The scientific study of heredity: how particular qualities or traits are transmitted from parents to offspring.
Genome: The sum of all the genetic material in the chromosomes of a particular organism.
Genome maps: Charts that indicate the ordered arrangement of the genes or other DNA markers within the chromosomes.
Genomics: The study of all of the nucleotide sequences, including structural genes, regulatory sequences, and non-coding DNA segments, in the chromosome of an organism.
Genotype: The actual genes carried by an individual.
Germ cells: The reproductive cells of the body, either egg or sperm cells.
Germline therapy: A gene is inserted into the DNA of the germline cells (egg or sperm) so that the offspring of the patient will have the inserted gene.

Hematopoietic stem cell: An unspecialized precursor cell that will develop into a mature blood cell.
Hemophilia: A hereditary bleeding disorder caused by the lack of certain clotting factors in the blood.
Hereditary mutation: A gene change in the body's reproductive cells (egg or sperm) that becomes incorporated in the DNA of every cell in the body; also called germline mutation.
Herpes viruses: Viruses which can affect the skin and central nervous system, includes Herpes simplex, Herpes zoster, and Cytomegalovirus.
Human genome: The full collection of genes needed to produce a human being.
Huntington's disease: An adult-onset disease characterized by progressive mental and physical deterioration; it is caused by an inherited dominant gene mutation.
Immunodeficiency: A state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Most cases of immunodeficiency are acquired ("secondary") but some people are born with defects in the immune system, or primary immunodeficiency.
Immunotherapy: Stimulates or restores the ability of the immune system to fight infection and disease. Research hopes to harness immune mechanisms against tumor cells, by using the patient's own immune system or the transfer of antibodies or T-cells from an outside source.
In vivo Gene Therapy: A vector carrying the therapeutic gene(s) is directly administered to the affected tissue.
Inborn errors of metabolism: Inherited diseases resulting from alterations in genes that code for enzymes.
Lentivirus: Viruses of the Retroviridae family, characterized by a long incubation period. HIV, SIV, and FIV are all examples of lentiviruses.
Leukemia: Cancer that begins in developing blood cells in the bone marrow.
Li-Fraumeni syndrome: A family predisposition to multiple cancers, caused by a mutation in the p53 tumor-suppressor gene.
Lymphocytes: Small white blood cells that plays a large role in defending the body against disease. Lymphocytes are responsible for immune responses. There are two main types of lymphocytes: B cells and T cells. The B cells make antibodies that attack bacteria and toxins while the T cells attack body cells themselves when they have been taken over by viruses or have become cancerous. Lymphocytes secrete products (lymphokines) that modulate the functional activities of many other types of cells and are often present at sites of chronic inflammation.
Melanoma: A cancer that begins in skin cells called melanocytes and spreads to internal organs.
Molecule: A group of atoms arranged to interact in a particular way; one molecule of any substance is the smallest physical unit of that particular substance
Multifactorial disorder: A genetically linked disorder that is not purely the result of heredity; they are the result of multiple gene mutations and environmental factors. Examples: cancer, diabetes, heart disease.
Mutation: Change in the number, arrangement, or molecular sequence of a gene. As a result, the gene no longer makes a normal copy of the protein that it encodes.
Newborn screening: Examining blood samples from a newborn infant to detect disease-related abnormalities or deficiencies in gene products.
Nucleotide: A subunit of DNA or RNA, consisting of one chemical base plus a phosphate molecule and a sugar molecule.
Nucleus: The cell structure that houses the chromosomes.
Oncogenes: Genes that normally play a role in the growth of cells but, when overexpressed or mutated, can foster the growth of cancer.
p53: a transcription factor encoded by the TP53 gene. p53 is important in multicellular organisms, where it regulates the cell cycle and thus functions as a tumor suppressor that is involved in preventing cancer.
Parkinson's Disease: A degenerative disorder of the central nervous system that often impairs the sufferer's motor skills and speech.
PCR: Polymerase chain reaction (PCR) is a key technique in molecular genetics that permits the analysis of any short sequence of DNA (or RNA) without having to clone it. PCR is used to reproduce (amplify) selected sections of DNA. PCR is highly efficient so that untold numbers of copies can be made of the DNA. .
Phenotype: The observable traits or characteristics of an organism, for example hair color, weight, or the presence or absence of a disease. Phenotypic traits are not necessarily genetic.
Plasmid: A circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA.
Poxviruses: Viruses associated with diseases that produced poxs in the skin. The smallpox virus remains as the most notable member of the Poxviridae family.
Preclinical Trial: Refers to the testing of experimental drugs in the test tube or in animals - the testing that occurs before trials in humans may be carried out.
Probe: A specific sequence of single-stranded DNA, typically labeled with a radioactive atom, which is designed to bind to, and thereby single out, a particular segment of DNA.
Promoter: A site on DNA to which the enzyme RNA polymerase can bind and initiate the transcription of DNA into RNA.
Prophylactic surgery: Surgery to remove tissue that is in danger of becoming cancerous, before cancer has the chance to develop. Surgery to remove the breasts of women at high risk of developing breast cancer is known as prophylactic mastectomy.
Protein product: The protein molecule assembled under the direction of a gene.
Protein: A large, complex molecule composed of amino acids. The sequence of the amino acids and thus the function of the protein is determined by the sequence of the base pairs in the gene that encodes it. Proteins are essential to the structure, function, and regulation of the body. Examples are hormones, enzymes, and antibodies.
Recessive allele: A gene that is expressed only when its counterpart allele on the matching chromosome is also recessive (not dominant). Autosomal recessive disorders develop in persons who receive two copies of the mutant gene, one from each parent who is a carrier.
Recombinant DNA: A novel DNA sequence formed by the joining, usually in vitro, of two non-homologous DNA molecules.
Recombination: A phenomenon that sometimes occurs during the formation of sperm and egg cells (meiosis); a pair of chromosomes (one from the mother and the other from the father) break and trade segments with one another.
Reproductive cells: Egg and sperm cells. Each mature reproductive cell carries a single set of 23 chromosomes.
Restriction enzymes: Enzymes that can cut strands of DNA at specific base sequences.
Retinoblastoma: An eye cancer caused by the loss of a pair of tumor-suppressor genes; the inherited form typically appears in childhood, since one gene is missing from the time of birth.
Retrovirus: A type of virus that contains RNA as its genetic material. The RNA of the virus is translated into DNA, which inserts itself into an infected cell's own DNA. Retroviruses can cause many diseases, including some cancers and AIDS.
RNA (ribonucleic acid): A molecule that is chemically similar to DNA and carries the same code. The several classes of RNA molecules play important roles in protein synthesis and other cell activities.
Sarcoma: A type of cancer that starts in bone or muscle.
Serious Adverse Event: Any untoward medical occurrence in human drug trials that at any dose results in: death, is life-threatening; requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, or is a congenital anomaly/birth defect.
Serotype: A group of closely related microorganisms distinguished by a characteristic set of antigens.
Sex chromosomes: The chromosomes that determine the sex of an organism. Human females have two X chromosomes; males have one X and one Y.
Sickle-cell anemia: An inherited, potentially lethal disease in which a defect in hemoglobin, the oxygen-carrying pigment in the blood, causes distortion (sickling) and loss of red blood cells, producing damage to organs throughout the body.
Somatic cells: All body cells except the reproductive cells.
Somatic Therapy: Involves the manipulation of gene expression in cells that will be corrective to the patient but not inherited by the next generation. Somatic cells include all the non-reproductive cells in the human body.
Stem cell: A progenitor blood cell made in the bone marrow that can give rise to all the cells of the blood and immune system, including red blood cells, white cells to fight infection, and platelets for clotting.
Suicide gene: A strategy for making cancer cells more vulnerable to chemotherapy. One approach has been to link parts of genes expressed in cancer cells to other genes for enzymes not found in mammals that can convert a harmless substance into one that is toxic to the tumor.
Tay-Sachs disease: An inherited disease of infancy characterized by profound mental retardation and early death; it is caused by a recessive gene mutation.
Transcription: The process of copying information from DNA into new strands of messenger RNA (mRNA). The mRNA then carries this information to the cytoplasm, where it serves as the blueprint for the manufacture of a specific protein.
Translation: The process of turning instructions from mRNA, base by base, into chains of amino acids that then fold into proteins. This process takes place in the cytoplasm, on structures called ribosomes.
Tropism: Refers to host tropism that is a process of tropism that determines which cells can become infected by any given pathogen. Various factors determine the ability of a pathogen to infect a particular cell. Viruses, for example, must bind to specific cell surface receptors to enter a cell. If a cell does not express these receptors then the virus cannot normally infect it.
Tumor-suppressor genes: Genes that normally restrain cell growth but, when missing or inactivated by mutation, allow cells to grow uncontrolled. P53 is a tumor suppressor gene.
Vaccinia virus: Virus is closely related to the virus that causes cowpox. It is in the pox family of viruses, which also includes smallpox. Vaccinia is so mild that it is typically asymptomatic in healthy individuals, but may causes a mild rash and fever, with an extremely low rate of fatality.
Vectors: Gene therapy delivery vehicles, or carriers, that encapsulate therapeutic genes for delivery to cells. These include both genetically disabled viruses such as adenovirus and nonviral vectors such as liposomes.
Viruses: Tiny organisms, smaller than bacteria, consisting of a protein coat and some nucleic acid. They only reproduce inside living cells and can cause disease.
Recommended video: "Understanding viruses"
Wilms' tumor: A kidney cancer (tumor) that occurs in children, usually before age five.
X chromosome: A sex chromosome, normal females carry two X chromosomes.
X-SCID: Severe combined immunodeficiency disease is a combined deficiency of the immune system's two major weapons, antibodies and T cells, are genetically missing or disabled. SCID is rare, the chances of a child being born with SCID are about one in 500,000 births. X-linked SCID, the most common type, is a genetic flaw damages molecules that allow T cells and B cells to receive signals from crucial growth factors.
Y chromosome: A sex chromosome, normal males carry one Y and one X chromosome.

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