what is retinitis pigmentosa?

Retinitis pigmentosa is the generic term for some eye diseases that are caused by a genetic defect and cause the sensory cells of the retina to die off. There are two types of these sensory cells. Both perish as a result of the disease: the rods, which are responsible for seeing through light and dark, and the cones, which make color recognition and sharp vision possible. techwadia

Retinitis pigmentosa develops slowly, often over several decades. It usually begins in adolescence or middle age. First of all , the person concerned notices that their vision becomes worse and worse in the evening ( night blindness ) and that their field of vision is gradually restricted. Later on, contrast and color vision as well as visual acuity deteriorate. In the late stages it can lead toCome blind . Usually both eyes are affected, in rare cases only one eye is affected.

Term: why do doctors use the term retinitis?

The term retinitis is actually misleading because it is not an inflammatory disease, as the (ancient Greek) word ending "-itis" usually indicates in medical parlance (for example arthritis (inflammation of the joints) or gingivitis ( inflammation of the gums )). Although the correct term is "retinopathia", the term "retinitis" has gained acceptance in medical parlance.
The adjective "pigmentosa" describes the pigment deposits in the retina.

Frequency: How often does retinitis pigmentosa occur?

In Germany, around 30,000 to 40,000 people suffer from retinitis pigmentosa, and around three million worldwide. Men are slightly more likely to suffer from the eye disease than women.

Development: How does retinitis pigmentosa develop?

The retina of the human eye has around 125 million light-sensitive sensory cells (also called photoreceptors). The main part, 120 million, are rods, 5 million are cones. Their job is to pick up light signals and convert them into electrical impulses. These are then transported to the brain via the optic nerve, where the image seen is then generated.

The rods are elongated and narrow and are mainly located on the edge of the retina. You are responsible for seeing light and dark. Since they already react to little light, people can see something even at dusk and in the dark. However, they only allow black and white vision.

The cones, on the other hand, are cone-shaped and are mainly located in the center of the retina, the so-called yellow spot (macula). They make color recognition and sharp vision possible and are only activated in brighter light. Thanks to their help, man is able to perceive the world in its different colors during the day.

There are three types of cone: red, green and blue cones, which convert the different wavelengths of light. They are also known as L (Long), M (Medium), and S (Small) cones, according to the long, medium, or short wavelengths of light to which they respond.

In retinitis pigmentosa, a genetic defect leads to a metabolic disorder in the organ of vision, for example, and the sensory cells then gradually die off. Initially, the rods are usually affected, later the cones also perish. As a result, the eyesight of those affected decreases more and more.

First they get severe visual problems at dusk, then the patient's field of vision narrows increasingly until after a certain time they only perceive a small section in the center (so-called tunnel vision) or blindness occurs.

Why do the sensory cells die?

So far, research has not yet clarified why the cones also die off. Because usually only the dying of the chopsticks is genetically determined. This may also be related to a special protein (RdCVF) that the rods release and that supplies the cones with glucose. If the rods are destroyed, the cones lack the RdCVF protein and thus the vital source of energy.

What types of retinitis pigmentosa are there?

Doctors basically differentiate between three groups of retinitis pigmentosa:

Primary retinitis pigmentosa

It is the most common form of retinitis pigmentosa, affecting more than 90 percent of patients. It is limited to the eye and no other organs are affected.

Associated retinitis pigmentosa

Around 25 percent of patients develop other physical complaints in addition to the eye disease, e.g. hearing impairment, muscle weakness, walking problems, very light-sensitive or flaky skin or cardiac arrhythmias .

In addition, retinitis can develop as a result of another hereditary disease, the most common of which is Usher's syndrome, in which those affected have congenital hearing loss or deafness, and in Bardet-Biedl syndrome, in which, among other things, metabolic disorders, excess fingers or toes and kidney diseases can arise.

Pseudo-retinitis pigmentosa

If the typical symptoms of retinitis pigmentosa occur, but the person concerned does not have a genetic defect, doctors speak of pseudo-retinitis pigmentosa. The cause of the eye disease can be, for example, inflammation, injuries, autoimmune diseases or side effects of medication.

Symptoms: what are the symptoms?

The classic sequence of symptoms: rod-and-cone dystrophy

Since the sensory cells responsible for light-dark vision (rods) are usually damaged first, vision problems arise at dusk at the onset of the disease. This means that those affected can no longer see (almost) anything in the evening or in an unlit environment. Night blindness (nyctalopia) is usually the first sign of retinitis pigmentosa!

During the day, those affected often have problems adjusting to rapidly changing light conditions (adaptation), for example when they go from a sun-drenched living room to the basement or from the foyer to the dark cinema room.

In the classic course of the eye disease, the field of vision is then increasingly restricted from the outside to the inside. The field of vision is the area that a person sees when looking straight ahead. Visual acuity is best in the center of the field of vision. It enables precise details to be recognized; although it is less precise in the outer zone (periphery), it is used for orientation in space.

With retinitis pigmentosa patients gradually no longer perceive the outer area of ​​the visual field. It disappears more and more until those affected can only see a small section in their field of vision - as if they were looking through a pipe (also known as a tube field of vision or tunnel vision).

The first indications of a restricted field of vision are: Sufferers often stumble over objects that they did not notice, although they were clearly visible to others. For example, they no longer notice the curb of a street or overlook it when someone waves to them.

Over time, sensory cells that enable color recognition and sharp vision are also damaged (cones). The patient therefore no longer recognizes colors correctly (this often begins in the blue area) and has problems with contrast vision (dark areas appear to be overlit by brightness). The latter also favors glare sensitivity. This can also arise if a patient also has cataracts .

In the later stages, the tunnel vision can become more and more narrow until the organ of vision finally no longer perceives light and blindness occurs.

Sometimes those affected can still read a book, but since their all-round vision and thus also their sense of direction are severely impaired, they still need a white cane. At first this seems contradictory and may arouse the suspicion in some people that the person concerned is simulating his or her vision problems. This is no means the case, but is solely due to the various visual impairments that occur with the eye disease.

Rare development: cone-rod dystrophy

The course can sometimes be exactly the other way round: the damage then affects the cones first and the visual problems begin in the middle of the field of vision. The edge zones with the sticks, however, are still preserved.
As a result, the person affected can no longer see clearly at close range and needs a magnifying glass to be able to read. But at the edge of the field of vision he still perceives a lot precisely and therefore has an intact sense of direction. Doctors call this a cone-rod dystrophy. However, this progression rarely occurs (only in one in 40,000 cases).

How long the process takes until the ability to see is severely impaired varies from patient to patient. In most cases, several years pass from the time of diagnosis to severe visual impairment or blindness.

Causes: What causes the eye disease?

Retinitis pigmentosa is caused by a genetic defect. This may have been inherited from the parents or it may have formed spontaneously in the person concerned (new mutation).

Science has now identified more than 57 genes that mutate into retinitis pigmentosa. Researchers discovered over 100 different mutations in just one of them, the so-called rhodopsin gene. A change in these corresponding genes has serious consequences for the photoreceptors of the retina. The gene mutation can, for example, cause a metabolic disorder to develop and certain substances to accumulate in the cells of the retina or to produce a protein that damages the cells.

In addition, the visual process can be impaired by incorrectly formed proteins, and the visual cells can no longer function properly. Various harmful chain actions cause the photoreceptors to die.

It is estimated that around one million people in Germany alone carry such a gene that is capable of causing retinitis pigmentosa in their offspring.

Inheritance of eye disease

To put it simply: inheritance from parents to children Every gene is present in two versions in humans: one gene version from the mother and the other from the father. There are 46 chromosomes in a cell, which are arranged in pairs.

22 of these chromosome pairs (autosomons) are built up in parallel, only with the 23rd, the sex chromosome pair (gonosomes), there is a difference: While women have two X chromosomes, men have an X and a Y -Chromosome, he received the latter from his father.

A gene mutation can be inherited from the mother or father and thus passed on from one generation to the next, but it can also arise from scratch in the child (spontaneous mutation). In addition, a damaged gene does not necessarily have to cause a disease, depending on whether this gene is dominant (dominant) or recessive (receding) and on which chromosone it is located.

The forms of inheritance

If a Renititis pigmentosa gene (RP gene for short) from one parent meets the healthy gene from the other parent, three different consequences are possible:

If the RP gene is dominant, the allele (characteristic expression of a gene) is sufficient for the eye disease breaks out. In this case, doctors speak of an autosomal dominant inheritance. It affects about 25 percent of all cases.

If, on the other hand, the mutated gene is recessive, the other gene version must also be damaged in order for rentitis pigmentosa to develop. In this autosomal recessive form, although both parents are carriers of an RP gene, they do not suffer from it themselves. If, on the other hand, the disease-causing gene is covered by a healthy gene, the person concerned does not become ill, but he carries the RP gene in a recessive variant and can in turn pass it on to his children. More than half of all patients suffer from the recessive form.

It is a special case when the faulty gene is on the mother's X chromosome. In a woman, the healthy copy of the gene on the second X chromosome can prevent the onset of the disease. This is known as X-recessive inheritance. Nevertheless, the mother can pass the disease on to her children. If the father is also ill, retinitis pigmentosa breaks out in a son who does not have a compensating X chromosome.

However, if the father is healthy, there is only a 50 percent risk of the male child becoming ill. The daughters who emerge from the latter constellation can be 50 percent recessive carriers of the gene, but 50 percent can also be free of the RP gene. About every tenth RP patient suffers from the sex-linked X-linked recessive form.

The severity of retinitis pigmentosa is also influenced by the type of inheritance: patients with an autosomal dominant inheritance have the most favorable course of the disease, in autosomal recessive and sporadic cases it usually develops moderately, in X-linked inheritance it often occurs the most severe progression.

What is the risk of passing the disease on to children?

Advice
on human genetics Patients who want to start a family can seek advice from an ophthalmologist or a specialist in human genetics. These provide detailed information about the probability of inheritance.
If one parent has an autosmoal-dominated gene variant, there is a 50 percent risk that the child will inherit the eye disease. If both parents are carriers of autosomal recessive gene mutations, the probability is 25 percent that the offspring will develop retinitis pigmentosa.
In general, it can be said that more than half of all RP patients do not have any sick children, provided the other parent is not related and has healthy eyes, explains the self-help association Pro Retina Germany eV

Genetic analysis
With the help of the molecular analysis the mutated gene can be identified, with a multi-gene panel even several genes. The examination results of the ophthalmologist and a family tree, in which serious illnesses are noted, are also relevant for this.
The costs of the molecular genetic laboratory test are usually covered by the statutory health insurances if there is a corresponding indication.