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IRDs
What Are Inherited Retinal Diseases?
Inherited retinal diseases (IRDs; also called “inherited retinal dystrophies or degenerations”) are a diverse group of rare eye diseases, characterised by the progressive loss of function or death of photoreceptor (light-sensitive) cells in the retina, resulting in associated vision loss or blindness. The underlying cause of all IRDs is the presence of a mutation(s) in genes involved in development and normal function of photoreceptors or other retinal cells.
It has been estimated that IRDs affect approximately 1 in every 3000 persons (more than 2 million people worldwide). IRDs can affect people of all ages – they are leading cause of vision loss in people of working age (16 to 64 years) and a common cause of visual impairment in childhood.
Genetics of IRDs
IRDs are caused by a gene mutation that is inherited from a parent. This led to the title of “Inherited Retinal Disease”. In the case of IRDs, the mutation affects genes that play an essential role in normal retinal development and functioning, leading to the degeneration of photoreceptors and other retinal cells and associated vision loss.
Scientific research has shown that IRDs are genetically diverse, with over 260 disease-related genes identified to date. In some cases the genes or mutations responsible are not yet known or not understood. However, ongoing research and genetic testing is advancing our knowledge of such genetic changes in order to find cures.
A small number of IRDs are caused by mutations in one single gene. For example, Choroideremia (CHM), a progressive condition where vision loss primarily affects males, is caused by a mutation in a gene called CHM. Stargardt disease is caused by a mutation in a gene called ABCA4.
For most other IRDs, affected people may have the same symptoms and the same disease but each person could have mutations in different genes. This is because mutations in many different genes can all have the same end result. For example, RP can be caused by mutations in one of 84 different genes, while cone-rod dystrophy can be caused by mutations in one of 33 different genes. Mutations in 20 different genes can lead to macular dystrophies (MD) and another 15 different genes can be responsible for congenital stationary night blindness.