Glossary

Acid: Chemical substance that, when dissolved in water, releases hydrogen ions with a positive electrical charge

Allergy: An important physiological reaction to contact with a factor that does not usually produce any in most people.

Desoxyribonucleic acid (DNA): Complex protein, the largest in the human body, a constituent element of chromosomes and a natural support for heredity.

ACTH: Acronym of “adreno-corticotrophic hormone”, English term for “corticostimulin”, a hormone secreted by the anterior lobe of the pituitary and targeting the cortex (the periphery) of the adrenal gland.

Alleles: Genes located opposite each other on the two chromosomes of the same pair. By extension, it also concerns DNA variations at the same locus.

Amino acids or amino acids: Organic acids characterized by the presence of an acid function and a basic function. These molecules unite to form chains (polypeptides) thanks to the neutralization and union of the acid function of one with the basic function of the other.

Antibodies: Proteins (globulins) made by certain white blood cells (lymphocytes) in reaction to the intrusion into an organism of a foreign substance (antigen).

Antigen: A substance foreign to an organism that, when introduced into it, causes an immune reaction specifically directed against it.

Apoptosis: Natural cell death, programmed genetically, allowing balance to be maintained during the constant cell renewal of the body. This mechanism also intervenes to eliminate aging, damaged or abnormal cells that are potentially dangerous for the proper functioning of the body. It is opposed to “necrosis” which is an accidental cell death due to toxic substances, germs, etc...

Autoimmunity: Presence in the body of an autoantibody that reacts specifically with a substance from the organism where it was manufactured. Autoimmunity is an exception to the rule of an organism's tolerance for its own tissues. It is responsible for autoimmune diseases in which the individual attacks himself.

Ankylosing arthritis: Synonym for chronic progressive polyarthritis.

Axon: Extension of the nerve cell (neuron) that transmits nerve impulses.

Astrocytes: Star-shaped CNS cells that play a role in supporting brain tissue and ensuring the transport of certain chemical mediators. It has recently been discovered that they also play a role in immune phenomena.

Base: Chemical substance capable in solution of fixing the hydrogen ion released by an acid and therefore of neutralizing it.

Character: Set of distinctive traits of a person or group transmitted by inheritance or resulting from changes made by the environment.

Chromosome: Rod-shaped structure located in the nucleus of any living cell and serving as a support for genes that transmit the hereditary characteristics of an individual.

Cloning: In vitro recombination of DNA in an organism capable of replication.

Clone: Set of all cells derived from a single mother cell. They are therefore strictly identical from all points of view.

Code: A term used in genetics to refer to the transmission from a gene of the information necessary for the synthesis of a protein.

Cognitive: Refers to all intellectual functions (memory, attention, intelligence, etc.).

Major histocompatibility complex: Molecules located on the surface of the cells that make up a tissue that make it possible to recognize the genetic and immune characteristics of an individual. These molecules must be identical to allow an organ to be transplanted from one person to another.

Trimolecular complex: Set of three structures, the keystones of antigen recognition: 1, major histocompatibility complex (HLA) on the membrane of the antigen-presenting cell; 2, the antigen itself; 3, the T cell membrane receptor (TCR).

Corticosteroid: Refers to hormones secreted by the peripheral part (cortex) of the adrenal gland and synthetic products that have a similar action.

Cytokine: Chemical mediator secreted by a cell belonging to the immune system.

Deletion: Loss of a segment of DNA with restoration of the continuity of the molecule.

Link imbalance: Is said when two alleles corresponding to two distinct loci on the same chromosome are associated more frequently in a study population than would have been expected by chance.

Antigenic determinant: Synonym of epitope, fragment of an antigen recognized by the immune system.

Genetic distance: Interval between two loci on a genetic map, calculated based on the frequency of combinations.

Dizygote: Synonym for heterozygote.

Dominant: An allele that expresses its phenotype when it is present both heterozygotically and homozygotically.

Dysarthria: Speech disorder resulting from a lack of coordination of the muscles responsible for the articulation of words.

Encephalitis: Inflammatory or infectious disease of the brain, that is to say of the brain. It is most often of viral origin.

Experimental allergic encephalitis (EAE): Immune reaction in the central nervous system caused in animals by the subcutaneous injection of a mixture of proteins constituting brain tissue, killed tubercle bacilli and an oily substance that delays resorption (adjuvants).

Restriction enzyme: An enzyme that cleaves the two DNA strings at a specific sequence level.

Enzymes: Proteins that dramatically increase the speed of a chemical reaction without appearing to be involved. They result from the association of two molecules: the apoenzyme, which only allows the reaction with a single specific substance, and the coenzyme, which allows only one type of reaction on this substance.

Epitope: Fragment of an antigen recognized by various structures (antibodies, cell receptor for a T cell, etc.) responsible for identifying molecules foreign to the body. An antigen is never recognized in its entirety but at the level of one or more of its epitopes.

Functional: Refers to disorders that reflect the abnormal functioning of an organ: diarrhea, cough, etc... This term is more frequently used to refer to disorders that exist when no anomaly in the organs concerned is detectable.

Gamma globulin: Blood protein belonging to the globulin group. All antibodies belong to the gammaglobulin class and are secreted by B lymphocytes.

Gene: Elementary particle of deoxyribonucleic acid in which a hereditary character is registered. It includes all the DNA sequences involved in the production of the polypeptide chain corresponding to this character.

Genotype: Set of the hereditary characteristics of an individual.

Germ:Synonym for microbe.

Globulin: One of the two types of proteins contained in the blood along with albumin. They are large molecules, which are separated by electrophoresis into different fractions: alpha, beta and gamma.

Carbohydrates: General term for sugars and including “oses” (simple sugars) and “osides” (complex sugars).

Heterozygote: Individual who, for a given hereditary characteristic, carries two different genes, located opposite each other (alleles) on two chromosomes of the same pair, one coming from the father, the other from the mother.

Homozygote: Individual who, for a given hereditary characteristic, carries two identical genes, located opposite each other (alleles) on two chromosomes of the same pair, one coming from the father, the other from the mother.

Immunity: State of resistance of an organism to an external toxic or infectious agent. Natural immunity is hereditary; acquired immunity develops after initial contact with an external agent.

Immunoglobulins: Globulins, that is, one of the two types of proteins circulating in the blood that have immune properties. They are the material support for antibodies.

Immunosuppressive: A chemical substance that greatly decreases or suppresses immune reactions.

Incidence: Number of new cases of a disease observed during a calendar year in a given region.

Genetic link: Simultaneous separation and isolation of two or more genes due to their proximity on a chromosome.

Cerebrospinal fluid: Fluid that bathes the central nervous system, located around the spinal cord and the brain, as well as in cavities (ventricles) in the depth of the latter. It plays an important role in the evacuation of chemical substances involved in brain function. Taken by lumbar puncture, its analysis gives a reflection of what is happening in the central nervous system.

Locus (plural loci): Position of DNA sequences on a chromosome, whether genes or DNA fragments, with no known function (anonymous).

Lod score: Decimal logarithm of the ratio between the likelihood of genetic link between two loci and the likelihood of no link, calculated for a given genetic distance.

Lymphocyte: White blood cell that differs from others in that it is not formed in the bone marrow but in special organs called “lymphoid” (lymph nodes, spleen, etc.). They are divided into two main classes: T and B.

Memory lymphocytes: Lymphocytes responsible for maintaining for many years the memory of the molecular structure of one or more epitopes of an antigen during its first intrusion into the body in order to trigger an immediate immune reaction if it enters a second time, even much later.

Suppressor lymphocytes: Group T lymphocytes intervening to slow down or stop an immune reaction. T suppressor in English, they are recognized by the monoclonal antibody CD8.

T cells: T cells play a crucial role in cellular immune mechanisms and maintain the memory of contact with an antigen. They have a very long lifespan of up to ten years. They are recognized by the monoclonal antibody CD3.

Inducing lymphocytes: Group T lymphocytes intervening to trigger an immune reaction. T helper in English, they are identified by the monoclonal antibody CD4.

B cells: B lymphocytes are involved in immune mechanisms involving chemical mediators (humoral immunity). They can present the antigen to T cells and are responsible for making antibodies.

Lymphokin: Chemical mediator secreted by a lymphocyte.

Macrophage: Cell whose role is to absorb and destroy various particles (cellular waste, foreign bodies and in particular infectious germs, etc...). Most of them are of blood origin (monocytes).

Genetic marker: Genotypic or phenotypic character that makes it possible to identify a locus.

Mediator: “Chemical mediator” refers to a substance secreted by cells of the immune, nervous, or hormonal system, influencing the function of other cells. They transmit orders chemically.

Monoclonal: Refers to a chemical mediator secreted from cells that all come from a single parent cell.

Multiplex: Refers to a family in which several people with the same disease are observed.

Mutation: Modification of the genome's DNA sequence regardless of its type. A mutation involving only one base is said to be “punctual”.

Myasthenia: Muscle contraction disorder due to an interruption in the transmission of nerve impulses between the nerve and the muscle. It results from the presence of antibodies directed against the chemical substance responsible for transmission (acetylcholine).

Myelin: Sheath surrounding axons and made up largely of fats. It also contains proteins, the most important of which is the basic myelin protein. Its role is to save the energy necessary for the conduction of nerve impulses and to make this conduction more rapid.

Neuron: Nerve cell that participates in the development and transmission of nerve impulses.

Nucleotide: Chemical body resulting from the combination of a phosphoric acid, a carbohydrate and a base (puric or pyrinidic).

Nystagmus: Rhythmic, involuntary and combined twitching of the eyes. Translates to a lesion of the cerebellum or inner ear.

Oligodendrocyte: Brain tissue cell responsible for the manufacture and maintenance of myelin sheaths.

Organic: Refers to a disorder related to a detectable alteration in the structure of an organ as opposed to a functional disorder.

Paraclinical: Refers to laboratory tests and technical examinations carried out to confirm a diagnosis based on the observation of clinical disorders.

Penetrance: Percentage of individuals carrying a dominant gene and expressing the corresponding phenotype.

Phenotype: Term referring to all the characteristics of the individual that can be observed. When they are essentially the result of hereditary heritage, we speak of a “genotype”.

Plasmocyte: B lymphocyte secreting antibodies.

Evolutionary chronic polyarthritis: A chronic rheumatic condition triggered by antibodies directed against the wall (synovia) of the joints. Also called ankylosing polyarthritis, it is an autoimmune condition. Immunosuppressants effective in ECP are in theory interesting candidates for the treatment of MS.

Polymerase chain reaction (PCR): Elective enzymatic amplification of a DNA sequence by exponential duplication during successive cycles.

Restriction polymorphism: Individual variation in the genome sequence revealed by digestion with a restriction enzyme.

Prevalence: Number of people with the same disease in the same region at a given time.

Protein: Substance resulting from the assembly of amino acids. It is composed of several chains. The amino acid sequence defines the primary structure that is sensitive to the action of enzymes. These primary chains are wound helically and this structure, called secondary, is maintained by hydrogen chains. These propellers are themselves associated or folded. Maintained by disulphid bridges, they constitute the tertiary structure. These last two structures are very sensitive to the action of physical agents (temperature, acidity, etc.).

Recessive: An allele that expresses its phenotype only in a homozygotic state.

Satellites: Short amino acid sequences that are easily identified with the genetic analysis technique thanks to their small size. When they are located near a gene (hence their satellite names), they make it possible to identify it indirectly, much easier than its direct identification.

Amyotrophic lateral sclerosis (ALS): A degenerative condition of the central nervous system, characterized by the gradual disappearance of motor cells in the spinal cord and brain stem. It is frequently called “Charcot's disease” in French-speaking countries.

Segregation: Separation and isolation of the homologous chromosomes and therefore of the allelic genes that they carry.

Sporadic: Disease affecting only a few isolated individuals within a population.

White substance: Brain tissue made up of all myelinated axons.

Gray matter: Brain tissue made up of all nerve cells (neurons).

Sugar: Organic substance belonging to the carbohydrate group. Simple sugars (molecules with 5 or 6 carbons) provide energy like glucose; others are involved in the constitution of important molecules such as nucleic acids responsible for genetic transmission (ribose, deoxyribose, etc.).

Systemic: Medical term for anything that relates to general blood flow.

Translation: Synthesis of a polypeptide chain from a messenger RNA.

Transcript: Synthesis of RNA from a DNA fragment.

Transfection: Acquisition of a new genetic marker by incorporating DNA into a cell.

Translocation: Transfer of one chromosome fragment to another.

Brain stem: Part of the CNS that connects the brain and the cervical spinal cord. It contains the centers corresponding to the various functions of the head and neck as well as the regulatory centers of the main vital functions (heart rate, breathing, blood pressure, consciousness, etc.).