What causes an inherited retinal disease?
An inherited retinal disease is caused by a variation in your genetic code or DNA.
You can think of DNA as a recipe book, which contains all the instructions needed for your body to make the proteins to survive and thrive. Proteins are important as they provide cell structure, function and regulation of the body. In genetic diseases, there is an error in one of the recipes, which can lead to disease.
In IRDs, the genetic error usually results in an abnormality of the photoreceptor cells in the retina. The retina is the light-sensitive tissue at the back of the eye that senses and transmits light signals to the brain through the optic nerve to form images, enabling people to see.
Over 300 IRD associated genes
Researchers have found over 300 genes that cause IRDs.
Some IRDs, such as choroideremia or juvenile X-linked retinoschisis, are caused by one or only a small number of genes (known as a “monogenic” disease). Other diseases can be caused by many different mutations in many different genes. For example, over 70 different genes have been identified that can cause retinitis pigmentosa. Some gene anomalies cause more severe inherited retinal diseases than others.
60% successfully diagnosed
Currently, we are only able to find the causative gene mutation for about 6 in 10 people. This is because we still do not know all the genes that cause IRDs and, in some cases, our testing is not sensitive enough to detect certain changes in the genetic information.
However, researchers are working on more sensitive ways to examine a person’s genetic code in more detail, which should improve this number over time.
The way that each IRD is passed from generation to generation (inheritance pattern) can be different in each family.
- You may have a strong family history and know a family member with the condition.
- Or you may be the first one in your family to be diagnosed.
The different inheritance patterns of IRDs mean that there are different chances of children inheriting a condition, depending on the pattern. For example, recessive conditions can skip generations, whereas dominant inheritance is more likely to be present in most generations. In addition, it is possible for a person to develop an entirely new genetic mutation – this is known as a “de novo” gene variant. For more details, refer the “Inheritance Patterns” section.
In most people, IRDs only affect the eyes. However, some types are linked with other health issues, such as Usher syndrome (which also affects hearing).