Rare Retinal Disease Glossary

Achromatopsia: Achromatopsia is a non-progressive and hereditary visual disorder characterized by the absence of color vision, decreased vision, light sensitivity and nystagmus (repetitive and uncontrolled eye movements). The disorder is caused by the absence of functioning cones (photoreceptors) in the retina.

AONs – Antisense oligonucleotides:  AONs are short, single-stranded DNA molecules that interact with messenger RNA to prevent translation of a targeted gene.

Autosomal chromosome: Any chromosome except for the sex chromosomes. Humans have 44 autosomal chromosomes, or autosomes.

Autosomal Dominant: Autosomal Dominant is a pattern of inheritance in which an affected individual has one copy of a mutant gene and one normal gene on a pair of autosomal chromosomes. (In contrast, autosomal recessive diseases require that the individual have two copies of the mutated gene.) Two genes associated with LCA (IMPDH1 and OTX2) are known to cause dominant disease. Twenty-four of the genes associated with LCA cause recessive disease. 

Autosomal Recessive: Autosomal Recessive is a pattern of inheritance in which an affected individual inherits two copies of the mutated gene, one from each parent. LCA is usually inherited as an autosomal recessive genetic condition.

BBS – Bardet Biedl Syndrome: BBS is a complex disorder affecting many parts of the body, including the eyes through retinal degeneration similar to RP.

Braille Writer: A Braille Writer, also known as a Brailler, is a typewriter used to emboss paper with braille cells to be read by the visually impaired. 

Choroideremia: Choroideremia is a condition characterized by progressive vision loss that mainly affects males. The first symptom of this condition is usually an impairment of night vision (night blindness), which can occur in early childhood. 

Clinical Trials: Clinical trials, monitored by the FDA, are research studies that explore whether a medical strategy, treatment or device is safe and effective for humans. They also may show which medical approaches work best for certain illnesses or groups of people. Clinical trials produce the best data available for health care decision-making.

Clinical Trial Phases: The FDA evaluates three study phases of a proposed new drug:

Phase 1 investigation of new drugs in humans focuses on the safety of a drug. Trials usually are conducted with healthy volunteers and usually involve a small number of participants. The goal is to determine the drug’s most frequent and serious adverse events and, often, how the drug is broken down and excreted by the body.  

Phase 2 consists of gathering preliminary data on whether the drug is effective in people who have a certain condition/disease. Participants receiving the drug may be compared to similar participants receiving a different treatment, usually an inactive substance called a placebo, or a different drug. Safety continues to be evaluated, and short-term adverse events are studied. 

Phase 3 research gathers more information about a drug’s safety and effectiveness by studying different populations and different dosages and by using the drug in combination with other drugs. These studies typically involve more participants.

Cones: Cones are one of two types of photoreceptors in the retina. They deliver  color vision and help discern fine details. They are concentrated in the center of the retina in an area called the macula. The retina has approximately 120 million rods and 6 million cones.

CVI – Cortical Visual Impairment: CVI is a visual impairment that occurs due to a brain injury.

CRISPR-Cas9: CRISPR-Cas9 is short for Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated protein 9. The CRISPR-Cas9 gene-editing technology developed by Editas Medicine and Allergan is designed to locate and remove the mutation in LCA10 or CEP290-LCA. The treatment works like a pair of molecular scissors to cut out the mutation, and it is delivered to photoreceptors by subretinal injection.

DNA – Deoxyribonucleic acid: DNA is the hereditary material in humans and almost all other organisms.

ERG – Electroretinogram: An ERG, also known as an electroretinography test, measures the electrical response of the eye’s light-sensitive cells. 

Endpoint: An endpoint is the primary outcome being measured by a clinical trial.

FDA – U.S. Food and Drug Administration: The FDA is an agency within the U.S. Department of Health and Human Services. It consists of the Office of the Commissioner and four directorates overseeing the core functions of the agency: Medical Products and Tobacco, Foods and Veterinary Medicine, Global Regulatory Operations and Policy, and Operations. The FDA is responsible for protecting the public health by assuring the safety, effectiveness, quality and security of human and veterinary drugs, vaccines and other biological products, and medical devices. The FDA also is responsible for the safety and security of most of the nation’s food supply, all cosmetics, dietary supplements and products that give off radiation.

FFB – Foundation Fighting Blindness: FFB is the world’s leading private source for inherited retinal disease research funding, driving the research of prevention, treatments  cures for retinal degenerative diseases.

Genetic Testing: Genetic testing is critical to confirming a suspected genetic condition. A genetic test identifies changes in chromosomes, genes or proteins. The results can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder. 

Genome: Genome is the complete set of genes or genetic material present in a cell or organism. Also, see HGP. 

Gene Therapy: Human gene therapy seeks to modify or manipulate the expression of a gene or to alter the biological properties of living cells for therapeutic use. It is a technique that modifies a person’s genes to treat or cure disease. Gene therapies can work by replacing a disease-causing gene with a healthy copy of the gene; by inactivating a disease-causing gene that is not functioning properly; and by introducing a new or modified gene into the body to help treat a disease.

Global Genes: Guided by its mission to eliminate the challenges of rare disease, Global Genes is a leading rare disease patient advocacy organization with worldwide reach that serves and promotes the needs of patients and families touched by rare and genetic diseases. 

HGP – The Human Genome Project: The HGP began in 1990 with an international collaborative quest to map and understand all the genes of human beings and their roles in health and disease. Completed in 2003, the HGP revealed there are probably about 20,500 genes, referred to collectively as our genome. 

IND – Investigational New Drug: An IND is a number assigned by the FDA, signaling the federal OK to proceed with clinical trials.

IRDs – Inherited Retinal Diseases: IRDs are a group of rare blinding conditions caused by one of more than 250 different genes.

LCA – Leber congenital amaurosis: LCA is a rare inherited eye disorder that causes severe vision loss at birth. It is the most common cause of inherited blindness in childhood and is found in two to three out of every 100,000 babies. LCA is monogenic, meaning the disease is caused by a single gene. At least 27 genes are implicated, and changes or mutations in these genes can account for about 80 to 90 percent of diagnosed LCA cases. The genes responsible for the remaining 10 to 20 percent of diagnoses are not known. LCA usually is inherited as an autosomal recessive genetic condition. 

Below are the pathogenic variants (variants that cause disease) in 17 genes known to cause LCA. Together, pathogenic variants in these genes are estimated to account for more than half of all LCA diagnoses.

LCA/RPE65 gene therapy trial: A clinical trial in which patients with a form of LCA called LCA2 or RPE65-LCA received gene therapy through subretinal injections of the human RPE65 gene. The therapy, called LUXTURNA, produced dramatic gains in visual sensitivity and received FDA approval in December 2017.

LUXTURNA®: LUXTURNA is the first FDA-approved prescription gene therapy for IRD patients with LCA caused by mutations in the gene RPE65, one of the more than 25 different genes, that, when mutated, can lead to LCA. Spark Therapeutics, a company that spun off the team’s research at Children’s Hospital of Philadelphia, developed the drug after 12 years of research and millions of dollars in investment. LUXTURNA is the first gene therapy for any inherited genetic disease in the United States, and it is the first genetic therapy targeting a retinal disease worldwide.

MRT – My Retina Tracker®: MRT is a free, secure online registry launched by the Foundation Fighting Blindness that helps connect families dealing with rare inherited retinal diseases to ease feelings of isolation and to find help. The registry also enables doctors and researchers to track the progress, prevalence and other variables of IRDs to move research forward.

NH – Natural History Study: A Natural History Study tracks the course of a patient’s disease over time. These studies identify demographic, genetic, environmental and other variables that shape the drug-development process. They give scientists and researchers a better estimate of the prevalence of the disease, help identify potential biomarkers, affect clinical outcome assessments, and determine the feasibility of established assessments for clinical trials.

NORD – National Organization for Rare Disorders: NORD, along with its more than 280 patient organization members, is committed to the identification, treatment and cure of rare disorders through programs of education, advocacy, research and patient services.

Nystagmus: Nystagmus is a vision condition in which the eyes make repetitive, uncontrolled movements. These movements often result in reduced vision and depth perception and can affect balance and coordination; they can occur from side to side, up and down, or in a circular pattern.

OMIM® – Online Mendelian Inheritance in Man: OMIM is a comprehensive, authoritative compendium of human genes and genetic phenotypes that is updated daily and available online.

OCT – Optical Coherence Tomography: An OCT is a non-invasive imaging test that uses light waves to take cross-section pictures of the retina.

Optogenetics: Optogenetics is a gene therapy under study in which light is used to control genetically modified retinal cells.

O&M – Orientation and Mobility: O&M training focuses on helping individuals who are blind or visually impaired to safely and effectively navigate their environment. 

Orphan drugs: Orphan drugs are medications or other medicinal products used to treat rare diseases or disorders. They are called orphan drugs because, due to their limited market, few pharmaceutical companies pursue research into such products.

Photoreceptors: Photoreceptors are special cells in the retina responsible for converting light into signals sent to the brain. Photoreceptors give us our color vision and night vision. Rods and cones are the two types of photoreceptor cells.

RAN – Rare Action Network® : RAN, part of NORD, the National Organization for Rare Disorders, connects and empowers a unified network of individuals and organizations with tools, training and resources to become effective advocates for rare diseases through national- and state-based initiatives. 

RDD – Rare Disease Day: RDD is held globally on the last day of February annually to raise awareness for rare diseases and improve access to treatment and medical representation for individuals with rare diseases and their families.

Retina: The retina is the sensory membrane that lines the inner surface of the back of the eye. It is composed of several layers, including one containing specialized cells called photoreceptors.

RP – Retinitis Pigmentosa: RP is a group of related eye disorders that cause progressive vision loss as the retina’s light-sensing cells gradually deteriorate. 

Rhodopsin: Researchers in 1989-90 identified the Rhodopsin gene as the genetic cause of RP.

RNA – Ribonucleic acid: RNA is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes.

Rods: Rods are one of two types of photoreceptors cell in the retina. They are sensitive to light levels and enable good vision in low light. They are concentrated in the outer areas of the retina and enable peripheral vision. Rods are 500 to 1,000 times more sensitive to light than cones. The retina has approximately 120 million rods and 6 million cones.

SCD – Sickle Cell Disease: SCD is a group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disorder have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle, or crescent, shape. The disease attacks various parts of the body, including the eyes and joints. 

SSH – Sofia Sees Hope: SSH generates awareness, raises funds for genetic testing and research, and provides outreach, support and education to those affected with LCA and other rare IRDs.

Stargardt Disease: Often diagnosed in childhood or adolescence, Stargardt Disease is an inherited form of macular degeneration causing central vision loss. The condition is sometimes referred to as juvenile or early-onset macular degeneration.

Translational Research: Translational Research is the process of applying knowledge from basic biology and clinical trials to techniques and tools that address critical medical needs.

USH2A – Usher Syndrome Type 2A: USH2A is a genetic condition characterized by hearing loss from birth and progressive vision loss, due to RP that begins in adolescence or adulthood. 

VA – Visual Acuity: VA means clarity of vision. 

Visual Evoked Potentia: is a non-invasive testing method that provides objective information about the function of the entire vision system. VEP provides a means to measure the complete visual pathway, from the lens to the visual cortex, to detect mechanical or neural abnormalities related to vision. These problems are often subtle and difficult to detect.

XLRP – X-linked Retinitis Pigmentosa: XLRP is an inherited condition caused by mutations in the RPGR gene and results in progressive vision loss in boys and young men.