Glossary of Terms

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FOP-related medical and research terms

We know that some of our documents are highly technical to read, so we encourage the use of this glossary to help make better sense of the scientific aspects of FOP. Please don't hesitate to contact the IFOPA with any questions concerning this glossary. 

Glossary has been composed by Dr. Frederick S. Kaplan, Dr. Eileen Shore and Rishi R. Gupta.


Adenovirus: A family of DNA viruses that is used as a vehicle for the delivery of genes in many forms of gene-therapy.

Allele: One of the alternative versions of a gene (i.e variation in DNA sequence) that occurs at a specific chromosomal locus (site).

Ambient: In the environment. Commonly used: “ambient temperature” = temperature in the current environment.

Aminobisphosphonate: A type of bisphosphonate drug, which is (ironically) a potent inhibitor of osteoclast-mediated bone resorption and also a potent inhibitor of angiogenesis (new blood vessel formation) – a process that is necessary for new bone formation.

Animal model: An animal sufficiently like humans in it anatomy, physiology, or response to an injury that is used in medical research in order to obtain information that can be extrapolated to human medicine.

Angiogenesis: The formation of new blood vessels.

Anti-angiogenic: The property of preventing the formation of blood vessels.

Antigen: Typically a foreign (not naturally occurring in the body) protein that is capable of stimulating an immune response.

Anti-neoplastic: Inhibiting or preventing growth and spread of tumors.

Apoptosis: A genetically determined self-destruction of cells that is thought to exist to mediate the orderly elimination of unnecessary cells. Frequently described as “programmed cell death.”

Athymic: Lacking a thymus. The thymus is the site of production of T lymphocytes, a vital part of the adaptive immune system.

Autoregulatory Negative Feedback Loop: A physiological thermostat that dampens and regulates the response of a system to external input.


Base pair: One of the pairs of chemical bases in the DNA double helix that carries genetic information.

Bioinformatics: The collection, classification, storage, and analysis of biochemical and biological information using computers, especially as applied to molecular genetics and genome sequencing.

Blastocyst: One of the earliest stages of an embryo.

Bone Morphogenetic Protein (BMP): A family of potent proteins involved in the promotion of bone formation. The study of these proteins and their related pathways forms a core component to the study of FOP.


Candidate gene: A gene that is suspected of being involved in a disease. Candidate genes may be identified by their location in a chromosomal region that has been linked to the disease and/or by what is known about the cellular function of the protein product encoded by the gene (often of the same name).

Chromosome: One of the DNA-containing structures of the cell that contain most or all of the genes of the individual.

Crystallography: 3D structure of the molecule : A science that deals with the forms and structures of crystals. A molecule forms a three-dimensional structure and this is the study of that specific structure and how it relates to cellular processes.

Clathrin: The major component protein of a cage-like structure that is important in brining proteins from the outside to the inside of a cell.

Corticosteroids: Any of various chemical made by the adrenal gland and used medically, especially as anti-inflammatory agents.

Cyclooxygenase-2 (cox-2) Inhibitors: Any of a class of drugs (as celecoxib or rofecoxib) that selectively block the COX-2 enzyme but not the COX-1 enzyme. These drugs are intended to relieve pain and inflammation while minimizing gastrointestinal side effects – called also COX-2 blockers.


DNA (deoxyribonucleic acid): The molecule that encodes the genes responsible for the structure and function of living organisms and that transmits genetic information from one generation to the next. DNA molecules, localized mainly in cell nuclei, are constructed of a double helix held together by hydrogen bonds between purine and pyramidine bases which project inward from two chains containing alternate links of deoxyribose (a sugar) and phosphate.


Ectopic: Occurring in an abnormal position or place.

Endochondral: Relating to bone formation that take place on a cartilage scaffold.

Endocytosis: Incorporation of substances into a cell by a process where the cell membrane invaginates to form vesicles.

Endosome: A cellular structure that is involved in the transport of proteins from the outside to the inside of the cell.

Endothelial cells: Polygonal, elongated cells that form the entire lining of the vascular system (the endothelium). Their structure and functional integrity is fundamental to the integrity of vessel wall and the circulation.

Exon: A genetic sequence that codes information for the formation of a protein and that is copied and spliced together with other such sequences to form messenger RNA – also see INTRON.

Exostoses/osteochondromas: A specific type of benign bony outgrowth from a bone that occurs near the growth plates by an endochondral process.


Fibroblast growth factors (FGF): A family of protein growth factors involved in new blood vessel formation, wound repair, lung maturation, and the development of skeletal muscle, specific lineages of blood cells and bone marrow stroma. FGFs are recognized by a family of cell surface receptors that have the ability to catalyze reactions inside the cell after they are activated by the FGFs.

Fibroproliferative: Of or relating to the growth and proliferation of fibroblasts, the most basic connective tissue cell.

Fibrous: Containing, consisting of, or resembling fibers. b : Characterized by fibrosis. c : capable of being separated into fibers.


Gene: A specific sequence of DNA or RNA that is located on a chromosome. A gene is the functional unit of inheritance controlling transmission and expression of one or more traits by specifying the structure of a particular protein.

Gene therapy: The insertion of normal or genetically altered genes into cells, usually to replace defective genes especially in the treatment of genetic disorders.

Genome-Wide Linkage Analysis: The study of the relationship between genetic markers of affected vs. unaffected individuals in a family with a genetic disease in order to localize chromosomal region of the gene responsible for the disease.

Genotype: The genetic composition (alleles) of an individual in total or at a specific locus.

Glucocorticoids: Synonymous with corticosteroids.

Glycoprotein: A protein-conjugate with a carbohydrate (sugar) component.

Gradient: Change in the concentration of a substance with distance from the cell that makes the substance.

Gremlin: The name of a specific secreted BMP antagonist (inhibitor).


Heparin: type of long chain sugar that is found especially in liver, that prolongs the clotting time of blood, and that is used medically.

Heparin Sulfate Proteoglycans (HSPGs): Ubiquitous macromolecules associated with the cell surface and extracellular matrix of a wide range of cells of vertebrate and invertebrate tissues. They are essential cofactors in cell-cell recognition systems, in receptor-growth factor interactions, and in internalization of receptors.

Heterogenous: Consisting of dissimilar or diverse ingredients or constituents.

Heterotopic Ossification: Bone formation that occurs in an abnormal place. Synonymous with ectopic.

Heterozygous: Having two different alleles at corresponding loci on homologous chromosomes in a cell.

Histology/Histopathology: A branch of anatomy that deals with the minute structure of animal and plant tissues as discernable with the microscope.


Immunology: A science that deals with the immune system.

In vitro: Outside the living body/in an artificial environment.

In vivo: Within the living body.

Integrins: Cellular sensors that act as signaling molecules.

Intron: A segment of a gene that is transcribed to RNA but then is removed from the primary RNA transcript by splicing together the sequences (exons) on either side of the intron.


Lesion: An abnormal lump or bump.

Ligand: Usually refers to a protein like BMP that is secreted and binds to a receptor (often on the surface of a cell).

Lymphoblastoid: Describing a peripheral blood lymphocyte immortalized by a virus such as Epstein-Barr virus (EBV).

Lymphocyte: Any of the colorless mobile cells originating from stem cells and differentiating in lymphoid tissue (as of the thymus or bone marrow).

Lymphocytes are the typical cellular elements of lymph (or tissue fluids), include the cellular mediators of immunity, and constitute 20 to 30 percent of the white blood cells of normal human blood. 

Lysosome: a saclike structure within cells that contains various enzymes that break down other cellular products.

Mast cell: A large cell that exists mainly in connective tissue. Mast cells have a colorful granules containing substances (as histamine and heparin) that act as molecular toolkits to mediate allergic reactions and stimulate tissue repair.

Matrigel: a liquid preparation that is extracted from mouse tumor cells and is rich in extracellular matrix proteins. Its major component is laminin, followed by collagen IV, heparan sulfate proteoglycans, and entactin. At body temperature, the matrigel polymerizes to form a matrix of connective tissue proteins. It is often used as a carrier substance for the injection of proteins such as BMPs.

Meiosis: The cellular process that results in the number of chromosomes in gamete-producing cells (eggs and sperm) being reduced to one half. One of each pair of homologous chromosomes passes to each daughter cell.

Microarray Gene Expression Studies: Used to quantitatively examine the expression of RNA for thousands of genes in the genome. Gene expression refers to the transcription of gene from the stable DNA code into the less stable RNA intermediate that is used by the cell to direct the formation of proteins. In order to identify abnormal gene expression, we use gene chips (a key component of this technology), which are sensitive to mRNA levels in a particular sample, to assay the expression level of >30,000 individual genes at one time. This strategy allows us to determine how these genes respond in any particular single situation. If a gene behaves differently in a disease state vs. a normal state, then it can be inferred to have something to do with the disease.

Mitochondria: Any of various round or long cellular organelles that are found outside the nucleus, produce energy for the cell, and are rich in fats, proteins, and enzymes.

Mitotic Recombination: Any process of cell division that generates a diploid daughter cell with a re-assorted combination of genetic information (alleles).

Monoclonal: Derived form a single cell.

Monocytes: A large white blood cell that is formed in the bone marrow, enters the blood, and migrates into the connective tissue where it differentiates into a scavenger cell involved in the body's immune defense systems.

Morphogen: A diffusible protein that exerts control over tissue formation especially by forming a concentration gradient.

Morphology: (a) A branch of biology that deals with the form and structure of animals and plants; (b) the form and structure of an organism or any of its parts.

Mutation: A change in the DNA sequence that usually leads to a disease.

Mutein: A genetically engineered protein arising as a result of a laboratory-induced mutation.

Myosin: A fibrous protein of muscle that can split ATP, an energy molecule, and that reacts with actin to form actomyosin (not to be confused with Actinomycin : A type of drug that has the capability of inhibiting the transcription of mRNA from DNA.)


Neoplasm: New growths that should not be where they are. A tumor. An FOP lesion.

Noggin: The name of a specific secreted BMP antagonist (like gremlin). If BMP is a bone making signal, noggin is a “stop making bone” signal.

Nucleus: Substructure within cells that contain chromosomes (DNA).

Nucleated: Having a nucleus or nuclei.


Osteoclast: A large multinucleated cell whose sole responsibility is to resorb (eat up) bone. These cells are derived from blood-forming stem cells in the bone marrow.

Osteogenesis: The development and formation of bone.


Pathogenesis: The origination and development of disease.

Pathology: (a) The study of the essential nature of diseases and especially of the structural and functional changes produced by them; (b) Something abnormal; (c) The structural and functional deviations from the normal that constitute disease or characterize a particular disease.

Pathophysiology: The physiology of abnormal states; specifically, the functional changes that accompany a particular syndrome or disease.

Perichondrium: The membrane of fibrous connective tissue that surrounds cartilage, except at joints.

Peripheral Blood: The fluid that circulates in the heart, arteries, capillaries, and veins of an animal. Peripheral blood carries nourishment and oxygen to and brings away waste products from all parts of the body.

Perivascular Cells: Cells surrounding a blood vessel.

Phenotype: The visible properties of an organism that are produced by the interaction of the genotype and the environment.

Phosphorylation: The process of adding a phosphate group to a molecule. This often activates the molecule by altering its shape or charge and allows it to participate in a chemical reaction.

Physiology: (a) A branch of biology that deals with the functions and activities of life or of living matter (as organs, tissues, or cells) and of the physical and chemical phenomena involved; (b) The organic process and phenomena of an organism or any of its parts or of a particular body process.

Positional cloning: A technique used to identify genes, usually those that are associated with diseases, based on their location on a chromosome.

Preosseous: Tissue that is at an intermediate stage between undifferentiated connective tissue and bone.

Prostaglandins: A type of fatty acid that is made from the enzymatic breakdown of cell membranes that perform a variety of hormone-like actions (as in controlling blood pressure or smooth muscle contraction).

Proteins: Any of numerous naturally occurring, extremely complex substances that consist of amino-acid residues joined by peptide bonds. Proteins include many essential biological compounds (as enzymes, morphogens, growth factors, structural proteins, hormones, or immunoglobulins).

Proteoglycans: Any of a class of high molecular weight protein-sugar polymers that are found especially in the extracellular matrix of connective tissue.


Radioimmunoassay: A method to measure the amount of a substance using an antibody against the substance for specificity and a radioactive label for detection and measurement.

Receptor Signaling: The process in which the binding of signaling molecules to cell surface receptors leads to activation of particular proteins that turn-on and turn-off genes.

Receptor Trafficking: The movement of receptors from one part of the cell to another (often associated with receptor activation at the cell surface and/or degradation within the cell.)

Recombinant-Genetically Engineered: A term used to describe the manufacture of a protein by “genetic engineering”; usually by using a cloned gene as a template for making a specific protein.

RNA: Any of various nucleic acids that contain ribose and uracil as structural components and are associated with the control of cellular chemical activities. RNAs may be intermediaries between DNA and proteins (as in messenger RNA) or may have specific structural or enzymatic activities as in ribosomal RNA, transfer RNA or inhibitory RNA.


Sarcoplasmic Reticulum: The specialized endoplasmic reticulum of cardiac muscle and skeletal striated muscle that functions especially as a storage and release area for calcium.

Satellite Cells: A reserve cell population located in skeletal muscle fibers that is responsible for growth, healing, and regeneration of skeletal muscle.

Sequencing Genes: To determine the DNA nucleotide sequence (the genetic code) of a gene.

Signal Transduction: The process by which extracellular signals are detected and converted into intracellular signals, that, in turn, generate specific cellular responses.

Squalamine: An example of a powerful anti-angiogenic molecule originally isolated from the liver of dogfish sharks.

Stem Cells, Hematopoietic and Mesenchymal: Stem cells are of embryonic origin and possess the properties of both self-renewal and differentiation into a wide variety of tissue types. There are many different types of stem cells among which include Hematopoietic and Mesenchymal. Hematopoietic Stem Cells (HSCs) have the properties to give rise to all known cell types in the blood-forming and immune (hematolymphoid) systems. The bone marrow also contains other non-hematopoietic cells termed mesenchymal stem cells (MSCs), that are capable of both self renewal and differentiation into bone, cartilage, muscle, tendon, and fat. MSCs are similar to HSCs in that they are very rare, existing at an estimated frequency of about 1 in 100,000 bone marrow cells.

Syndecans and Glypicans: Integral membrane proteins in the family of heparan sulfate proteoglycans.


Thalidomide: A sedative and hypnotic drug C 13 H 10 N 2 O 4 that has been the cause of malformation of infants born to mothers using it during pregnancy. Thalidomide acts as an antiangiogenic agent and therefore can be inhibitory for bone formation.

Transcription: The process of constructing a messenger RNA molecule using a DNA molecule as a template. The messenger RNA (mRNA) is the unstable intermediate in the formation of a protein. (If the DNA is the cookbook, the mRNA is the recipe copied from the cookbook to make the protein (the cake).

Transforming Growth Factor-Beta Receptors: A receptor on cell membranes that binds TGF-beta, a growth factor involved in a number of biological events important in normal and abnormal growth of cells and tissues.

Transgenic: Having chromosomes into which one or more “foreign” genes (genes from a different organism and/or genes that have been modified) have been incorporated either artificially or naturally.

Transposons (Jumping Genes): Mobile elements of DNA that can insert into new locations in the chromosomal DNA and that can affect the function of genes at or near the insertion site.


Vascular: Referring to a channel for the conveyance of a body fluid, such as a blood vessel or a lymphatic vessel.

Vector: A sequence of genetic material used to introduce specific genes into the genome of an organism. A carrier molecule.

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