Professor Michel Michaelides is Fighting Retinal Blindness from Retinitis Pigmentosa
What is Retinitis Pigmentosa?
The website www.rpfightingblindness.org.uk is an excellent resource for learning more about the inherited retinal disease called Retinitis Pigmentosa (RP).
If you think that you have a possible diagnosis of Retinitis Pigmentosa or your optician, GP or ophthalmologist has already diagnosed this condition; you should seek a referral to a retinal specialist experienced in advising on this condition. Retinitis Pigmentosa is a condition that affects young people. The condition causes visual impairment with tunnel vision and eventual loss of central vision. Retinitis Pigmentosa affects roughly 1 in 3000-4000 people.
Many exciting technologies are coming along helping research and the development of genetic management (gene therapy). Researchers are developing new technologies to help people maximise their vision, when at home and work when using computers, mobile phones, books, TV, and the radio. Many new text-to-voice software applications help young working adults maintain successful, busy jobs and lives.
Retinitis pigmentosa is in fact not just one condition. Retinitis Pigmentosa is the general name given to a group of inherited retinal conditions which all lead to the same gradual and progressive reduction in vision. The first signs of visual impairment are difficulties with night vision and reduced peripheral or side vision. Later, with disease progression, Retinitis Pigmentosa can affect your reading vision, detailed vision, colour vision and central straight ahead vision. The age at which the visual symptoms begin can be variable. The rate of deterioration differs considerably and can depend on the particular genetic type. Retinitis Pigmentosa is a very slowly developing disease often starting in young adulthood, with changes occurring in the vision over several years, rather than rapidly over months. Often, other members of the family also have Retinitis Pigmentosa.
Professor Michel Michaelides can advise and confirm the diagnosis and inheritance patterns.
What are the inheritance patterns?
There are three main inheritance patterns. There is autosomal recessive, autosomal dominant and X-linked inheritance. I will try and explain what these each mean.
In simple terms, autosomal dominant Retinitis Pigmentosa is due to a fault in one gene and affects men and women equally. An affected parent can pass the condition to their son or daughter. There is a risk of 1 in 2 (50%) of someone with autosomal dominant Retinitis Pigmentosa passing on the disease to one of their children.
Autosomal recessive Retinitis Pigmentosa affects men and woman equally because faulty genes are carried on the autosome, but the difference that it is necessary is for both parents to have the genetic fault to affect one of their children. In this way, an affected person inherits one faulty gene from each parent. The parents are ‘carriers’. The parent will have one normal and one defective copy of the gene. They don’t have any symptoms of Retinitis Pigmentosa, they are just carriers, and carriers have normal vision. If both parents are carriers, then the risk of them having a child with autorecessive Retinitis Pigmentosa is 1 in 4 (a 25% chance).
The last inheritance patterns for Retinitis Pigmentosa is X-linked, where there is a faulty gene on the X chromosome, and this affects mainly males, although females can be very mildly affected and occasionally severely affected. The sex chromosomes of a woman consist of an identical pair of X chromosomes, while men have an X and Y chromosome. A man with X-linked Retinitis Pigmentosa will have a faulty gene on his X chromosome, and therefore he will pass on this chromosome to all of his daughters, but none of his sons, who only receive his Y chromosome which does not have a copy of this gene. So, none of his sons will be affected, whereas all of his daughters will become carriers. The female carriers with the X chromosome containing the faulty gene will also have an X chromosome with a normal copy and this normal copy usually protects them from developing full features of X-linked Retinitis Pigmentosa.
Some carriers of X-linked Retinitis Pigmentosa may have some mild signs of the condition. These signs could be just
- changes either directly in their retina
- changes detectable with specialised imaging or abnormal function of the retina detected with electrophysiology, or
- mild clinical symptoms with night vision.
A female Retinitis Pigmentosa carrier will pass one or other of the X chromosomes to her children, so there is a 1 in 2 chance that a female carrier will pass on the X chromosome with the faulty gene. If that chromosome with the faulty gene goes to her son, he will have an X-linked Retinitis Pigmentosa. If it goes to her daughter, she will become a carrier just like her mother.
To summarise, an affected male cannot transmit X-linked Retinitis Pigmentosa to his sons, but all his daughters will become carriers, and the carrier female has a 50% risk or 1 in 2 chance of having an affected son and has the same risk of having a daughter who is carrier like herself.
I hope that does not sound too complex for you! Remember, Professor Michaelides at Clinica London can help sort your family tree and advise you about the risk of passing on Retinitis Pigmentosa if you are affected or a carrier. You can read more about Retinitis Pigmentosa and Professor Michaelides in my next blog post.
Professor Michaelides is a world expert on Retinitis Pigmentosa working at the UCL Institute of Ophthalmology and Moorfields Eye Hospital and seeing patients privately at Clinica London. He will be pleased to help advise on the diagnosis of Retinitis Pigmentosa and what type of genetic inheritance it will have.