Retinitis Pigmentosa (RP)
Description
Retinitis pigmentosa (RP) is a group of inherited eye diseases that affect the retina, the light-sensitive tissue at the back of the eye. RP causes progressive vision loss, starting with night blindness and peripheral vision loss, which can eventually lead to complete blindness. This blog post will delve into the intricacies of RP, encompassing its causes, symptoms, diagnosis, management strategies, and resources for those affected by this condition.
Genes Involved
RP is caused by mutations in a variety of genes that are responsible for the function of the retina. Some of the genes involved include:
- RHO: The gene for rhodopsin, a light-sensitive pigment in the retina.
- ABCA4: A gene involved in the processing of vitamin A in the retina.
- PRPH2: The gene for peripherin, a protein found in the outer segments of photoreceptor cells.
- CRB1: A gene that plays a role in the structure and function of the outer segments of photoreceptor cells.
- USH2A: A gene that is associated with both RP and Usher syndrome, a condition that combines hearing loss and vision loss.
This is not an exhaustive list, as there are many other genes that can be involved in RP.
Recognizing the Signs and Symptoms
The most common early symptom of RP is night blindness, difficulty seeing in low light conditions. This is followed by peripheral vision loss, meaning the side or ‘corner‘ vision starts to diminish. Over time, the field of vision shrinks, making it difficult to see objects that are not directly in front. Other symptoms may include:
- Floaters: Small, dark spots or shapes that appear to float in the field of vision.
- Photophobia: Sensitivity to light.
- Tunnel vision: A narrowing of the field of vision, resembling looking through a tunnel.
- Loss of central vision: In advanced stages, central vision may also be affected.
Causes
Retinitis pigmentosa is primarily an inherited condition, meaning it‘s passed down through families. The specific genes involved can vary, leading to different forms of RP. While most cases are inherited, some individuals develop RP without a family history. This can occur due to a spontaneous gene mutation or unknown environmental factors.
Inheritance/recurrence risk
RP can be inherited in several ways, including:
- Autosomal dominant inheritance: Only one copy of the mutated gene is needed to inherit RP, and there is a 50% chance of passing it on to each child.
- Autosomal recessive inheritance: Both parents must carry the mutated gene for their child to inherit RP. If both parents are carriers, there is a 25% chance of their child having RP, a 50% chance of being a carrier, and a 25% chance of not inheriting the gene.
- X-linked recessive inheritance: The mutated gene is located on the X chromosome, and primarily affects males. If a mother is a carrier, there is a 50% chance of her son inheriting RP.
- Mitochondrial inheritance: The mutated gene is located in the mitochondria, which are organelles within cells that provide energy. RP due to mitochondrial inheritance is less common than other types.
The specific mode of inheritance can influence the risk of recurrence in future generations. Genetic counseling can provide guidance on the likelihood of passing on the condition.
