28 November, 2024
What is an inherited retinal disease?
An inherited retinal disease (IRD) is a condition caused by a genetic anomaly that leads to loss of vision and in some cases, legal blindness.
They are also known as inherited retinal dystrophies or inherited retinal degenerations.
There are over 20 types of inherited retinal diseases. Depending on the disease, you may have vision loss at birth, or it may occur later in life.
What causes an inherited retinal disease?
Genetic error
An IRD 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. 1
Some IRDs, such as choroideremia or 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.
Inheritance patterns
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, see the “Inheritance Patterns” section on the Retina Australia website here.
Syndromic IRDs
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). 2
How many people live with an inherited retinal disease?
In Australia, it is estimated that ~ 1 in 1380 people are living with an IRD, which is around 19,000 people. 3 5
Disease progression
IRDs can affect individuals of all ages and genders and can progress at different rates. Some may be born with or experience vision loss in infancy or early childhood. Some may experience a gradual loss of vision later in life.
The prognosis of an IRD also varies – some people will lose all vision, whilst others will have more mild disease.
Common symptoms of IRDs
Each IRD is different, but common symptoms include:
- Low vision at night, or in dim or dark settings
- Loss of central and/or peripheral vision
- Sensitivity to light, glare and difficulty in bright light
- Farsightedness or shortsightedness
- Blind spots
- Colour differentiation difficulties or not seeing all colours
- Uncontrolled eye movements (nystagmus)
Vision loss can vary between different IRDs
In some conditions, only the central vision is lost, while others lose peripheral vision first, with a slow progression into the central vision areas. Some people will only ever have mild vision loss, whilst others can progress to lose all vision, also known as “no light perception” or “black-blindness”.
Your ophthalmologist may be able to give you some indication of the expected future for you based on your clinical presentation and genetic testing, but this is not an exact science. Sometimes, it can be unpredictable as to how the disease will proceed.
Obtaining a confirmed diagnosis through genetic testing is the only way to verify the exact gene anomaly(s) that is the underlying cause of an IRD. 6
This article has been supported by Novartis.
https://retinaaustralia.com.au/in-focus-inherited-retinal-disease/
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