Retinitis Pigmentosa (RP)

Frequently Asked Questions (FAQs)

• What is RP?
• What are the symptoms?
• Who does it affect?
• How quickly does it progress?
• Can the progress be halted and is there a cure?
• How is it diagnosed?
• How is it transmitted?
• Genetics of RP
• How is the type determined?
• What action can be taken by those affected?

What is RP?

Retinitis Pigmentosa (RP) is the name given to a group of degenerative diseases of the retina. The retina, at the back of the eye, is a thin sheet of interconnected nerve cells including the light sensitive cells (rods). It is here that light is converted into electrical signals to the brain where "seeing" takes place. In RP the rod and cone cells degenerate. Depending on the type of RP, the rate of progression varies.

What are the symptoms?

Usually the rod cells are the first to be affected. They are concentrated away from the centre of vision in the retina and are responsible for seeing in dim light. Thus, one of the earliest symptoms is often night blindness followed by loss of peripheral vision leading to "tunnel vision".

Cone cells in contrast are concentrated in the centre of the retina and are responsible for brightly detailed colour vision. In cases where the cone cells degenerate first, central vision becomes blurred and loss of colour perception occurs. Peripheral vision is initially retained.

Symptoms of RP are most often recognized in children, adolescents and young adults, with progression of the disease continuing throughout the individual’s life.

Although the majority of people with RP do not suffer from associated disabilities, it does happen. Deafness associated with RP in a condition known as Usher syndrome is one such disability.

Who does it affect?

The symptoms of RP may occur at any age but most commonly they appear in young adults. Generally speaking, the earlier the disease begins, the more severe the symptoms. Occasionally the disease is present at birth and can be diagnosed with appropriate testing at that time. RP is recognized as one of the most common inherited causes of blindness in people between the ages of 20 and 60.

How quickly does it progress?

Most patients have very gradual progression of symptoms, often over many years or decades. Generally, when other members of a family are affected, the rate of vision loss is usually similar. Different forms of RP advance at different rates.

Can it be treated?

To date, there is no known way to halt the degeneration of the retina or cure the disease. Transplants of the retina are not possible at this time and there is no convincing scientific evidence to demonstrate benefit from any treatment methods currently available. There are, however, a number of areas currently being researched that demonstrate great potential.

How is it diagnosed?

Whenever RP is suspected or is a concern, a person should be evaluated by an ophthalmologist (medical eye doctor). The disease is usually most difficult to diagnose in the earliest stages. Depending on the stage and type of the disorder, tests of vision function such as visual field, dark adaptation and electroretinograms (ERG) are made to determine the precise state of the retina.

How is it transmitted?

The conditions are genetic in nature however up to 50% of cases do not appear to be inherited but are sporadic with no previous family history. The cause of these cases cannot be explained.

Genetics of RP

Within the nucleus of every human cell reside a host of genes. Genes are the fundamental building blocks of life. Inherited from our parents, genes carry family traits like eye and hair colour, the shape of our face and even diseases like RP.

Genes are like computer programs containing sets of coded instructions. Each gene instructs the cell to create a specialized protein that performs a specific task for the cell. In retinal cells, some genes encode proteins that allow the cell to process light. Other genes encode proteins that uptake nutrients and eliminate waste from the cell. Still other genes encode proteins that form the cell walls and other structures within the cell.

Sometimes, the coded instructions within a gene become altered. These alterations, known as mutations, can confer a benefit, allowing the organism to better adapt to its environment. However, mutations can also interfere with the proper encoding of a protein. The resultant protein cannot perform its job within the cell, thereby hampering the cell’s well being and leading to disease.

Retinal cells are among the most specialized cells in the human body and depend on a number of unique genes to create vision. A disease-causing mutation in any one of these genes can lead to vision loss.

To date, 38 genes and loci have been identified that cause the three inheritance patterns of RP; Autosomal recessive, autosomal dominant or X-linked recessive RP.

Autosomal recessive forms of the disease occur when both parents are unaffected carriers of the same defective gene. The chance of a child of theirs being affected is 1 in 4 (the affected child must inherit the defective gene from each parent). The chances of a parent having an unaffected child who, like them, would be a carrier of the defective gene is 1 in 2. The chance of such parents having a child completely free of the RP gene is 1 in 4.

Autosomal dominant forms of the disease are characterized by expression of the disease in either males or females when only a single copy of the gene is defective. In such cases, it is typical that one of the parents is affected by the disease. Since the affected parent has one normal and one defective gene, the chance is 1 in 2 of any given offspring being affected by the disease.

X-linked (or sex linked) recessive forms occur in offspring in two ways. The fathers can be affected or mothers can be carriers of the defective gene. If the father is affected, all sons will be unaffected and all daughters will be carriers. If the mother is the carrier, 1 in 2 sons will be affected and 1 in 2 daughters will be carriers.

How is the type determined?

Family history is the single most important factor to determine the type of RP. Family members should be examined by an ophthalmologist. For example, some female carriers of the X-linked form can be identified by slight pigmentary change or a golden reflex in the retina.

What action can be taken by those affected?

Those affected by RP should seek the best information available from ophthalmologists about their particular condition. Depending on the condition, further action may be appropriate in the field of education, training and family planning.