Autosome: chromosome in which the genetic information does not determine sex.
Autosomal: describes a trait transmitted by a gene carried by a chromosome which is not linked to the determination of sex (an autosome).
Autosomal dominant disorder: genetic trait expressed by an individual for which the modified (mutated) gene transmitted is present on only one of two homologous chromosomes (a pair of identical chromosomes). The transmission of the trait by either mother or father alone is enough for it to be expressed.
Autosomal recessive disorder: genetic trait expressed by an individual having received the modified (mutated) gene from both mother and father.
Cell therapy (cellular therapy): therapy in which faulty cells causing disease are replaced by an injection of healthy cells, thus restoring altered cellular functions. Cell therapies are grafts or cellular transplants.
Clinical trial: research in which the participants or groups of participants are allocated to one or several medical interventions as of the beginning of the trial in order to evaluate their effects on the participants’ health. Clinical trials test medical drugs, cells and other biological products, surgical acts, preventive care etc. (WHO). These studies are often carried out after preclinical studies (e.g. molecular studies, studies of structure, cellular effects, animal effects…) with an experimental phase conducted on animal or cellular models in order to confirm the safety and interest of the treatment tested. Clinical trials are made up of four phases:
- Phase I: phase designed to assess tolerability, pharmacokinetics and metabolism of the substance tested.
- Phase II: phase designed to assess the Optimal Biological Dose (OBD) and the possible side effects of the substance tested.
- Phase III: phase designed for the comparative assessment of efficacy. After this phase, the results can be submitted to the European Health Authorities in order to obtain marketing authorisation.
- Phase IV: phase designed for long term post-marketing surveillance.
Clinical trials require authorisation of the health authorities or the ethical authorities of the country in which they take place.
Cone cells: light-sensitive cells primarily located in the macula. They represent 3 to 5% of the photoreceptor cells that make up the retina. They are involved in diurnal (daytime) vision, enabling colour vision, perception of detail and of the size or thickness of the points observed.
Dilated fundus examination: painless retinal exam enabling the diagnosis of serious retinal anomalies. This test is conducted by an ophthalmologist after pupil dilation with an adequate substance.
Electrooculography: test which measures the retina’s electrical activity at rest, which is to say without visual stimulation.
Electroretinogram: graph obtained by electroretinography. It is an analysis of the retina’s electrical response to light stimulation. It enables the verification of both rod and cone cells’ activities thanks to variations of the light’s colour and intensity. The test is conducted using electrodes placed on the cornea and skin.
Fluorescein angiography: test which consists of taking photographs of the fundus after having injected a fluorescent product (fluorescein) into the vein. The angiography enables us to see the eye’s blood vessels, especially those of the retina. It enables the diagnosis of certain eye diseases, and the guiding of certain treatments. This test is conducted externally (without hospitalisation) but requires pupil dilation. A similar test is the auto fluorescence of the fundus.
Fovea centralis: small pit located in the centre of the macula composed entirely of cone cells (light-detecting cells). It makes up the area of visual acuity (ability and quality of vision). The area surrounding the fovea centralis mainly contains rod cells.
Fundus (of the eye): concave interior surface of the eye which includes the retina, the fovea centralis and the macula amongst other structures.
Gene: physical and functional unit of heredity, expressing a particular trait transmitted by parents to their offspring. This segment of DNA which carries genetic information is located in a specific region (allele) of a chromosome.
Gene therapy: therapy in which normal copies of the gene(s) responsible for a condition are administered to a patient carrying a genetic mutation, in order to replace the faulty gene(s).
Hereditary macular dystrophy: eye disease characterised by the impairment of the central area of the retina. These diseases concern the retinal area called the macula. They are responsible for a decrease in visual acuity and cause severe visual impairment. They group together a clinically, genetically and physiopathologically varied set of diseases. The form of Stargardt disease linked to the ABCA4 gene is a form of hereditary macular dystrophy. The most frequent form is Age-Related Macular Degeneration (AMD or ARMD).
Homozygous: a person is said to be homozygous for a gene if they carry two identical copies (two alleles) of the gene at issue (two normal genes or two mutated genes), one on each chromosome of the same pair.
Heterozygous: a person is said to be heterozygous for a gene if they carry either two copies of the gene each with different mutations or one modified copy and one normal copy of the gene.
Lipofuscin: lipid cellular pigment, product of organelle degradation which, when accumulated, alters the functioning of certain cells (e.g. damage to retinal cells).
Macula (of the retina): area located in the fundus of the eye, in the centre of the retina. It is the area where light rays focus. The macula participates in: the central vision of elements located in the line of vision, the vision of detail (reading, writing, facial detail…) and the ability to see colour.
Optic nerve: set of axons that transmit information from the eye to the brain.
Pharmacology: science of the development of molecules which act on direct or indirect molecular mechanisms of biological systems. This method is used for treatment development.
Photoreceptor cell: light-detecting cells which convert light into electrical signals. There are two types of photoreceptor cells: cone cells and rod cells.
Prevalence: number of people found to have a given condition at a given time within a given population.
Rare diseases (orphan diseases): diseases which do not benefit from treatment. These diseases affect a limited number of people. This rarity causes problems for medical care and social coverage, the development of medical and scientific research… The European threshold which defines a disease a rare disease is 1/2000 people. Cf. website: www.orpha.net
Retina: section lining the inner surface of the eye, made up of several layers of cells (photoreceptor cells (cone cells and rod cells), bipolar cells and retinal ganglion cells). These cells participate in the transformation and transmission from light to an electrical signal to create an image. This is where vision occurs.
Retinal dystrophy: hereditary retinal disease affecting cells involved in vision, that is to say the photoreceptor cells: cone cells and rod cells. These diseases are responsible for a decrease in visual acuity and cause severe visual impairment. They group together a clinically, genetically and physiopathologically varied set of diseases. Retinitis pigmentosa is a form of retinal dystrophy.
Retinal pigment epithelium (RPE): cell layer situated between the photoreceptor cells and the choroid (part of the eye which contains its vessels). Its role is to nourish the photoreceptor cells.
Retinitis pigmentosa: hereditary retinal dystrophy caused by abnormalities of photoreceptor cells: cone cells and rod cells. It is characterised by pigment deposits visible in the fundus. This visual impairment leads to blindness. There is currently no cure. Research is underway, especially with the development and study of the artificial retina.
Rod cells: light-sensitive cells located in the peripheral retina. They represent 95-97% of the photoreceptor cells that make up the retina. They are involved in nocturnal vision (with low light intensity), enable black-and-white vision and ensure movement detection.
Stargardt disease: genetic disease of the fundus of the eye, characterised by damage to the macula, the central area of the retina involved in precise vision, vision of detail and colour vision. It is linked to an anomaly (mutation) of the ABCA4 gene.
Visual acuity: defines the ability and quality of vision. Its measurement determines the eye’s ability to identify distinct points according to the distance between them and the distance to the person’s eye. It is measured in tenths or diopters.
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