Retinitis pigmentosa

Retinitis pigmentosa is a group of inherited eye disorders characterized by the gradual deterioration of light-sensitive cells in the retina, leading to progressive vision loss.

Overview

Retinitis pigmentosa affects the retina, the layer of light-sensitive tissue at the back of the eye. In affected individuals, specialized light receptor cells called photoreceptors gradually deteriorate. While the condition typically affects both eyes (bilateral), the age of onset and the progression of the disease vary significantly among individuals.

Symptoms

The progression of vision loss in retinitis pigmentosa typically follows a specific pattern:

• Night vision loss: Often the first sign, appearing in childhood or adolescence, making movement in low light difficult.
• Peripheral vision loss: Blind spots develop at the edges of the visual field.
• Tunnel vision: Over time, peripheral blind spots increase and merge.
• Central vision impairment: Eventually, the center of the visual field is affected, hindering tasks like reading, driving, and recognizing faces.

Most individuals with retinitis pigmentosa become legally blind in adulthood.

Types

• Nonsyndromic retinitis pigmentosa: Occurs on its own without symptoms in other parts of the body.
• Syndromic retinitis pigmentosa: Occurs as part of a syndrome affecting other organs. The most common form is Usher syndrome, which combines retinitis pigmentosa with early-onset hearing loss.

Causes & Risk Factors

Retinitis pigmentosa is caused by pathogenic variants in more than 130 different genes. These genes are essential for the structure, function, or maintenance of the retina's two types of photoreceptors:

• Rods: Responsible for vision in low light. These typically break down first, leading to night vision impairment.
• Cones: Responsible for vision in bright light and color vision. These are lost later in the disease progression.

Commonly associated genes include RHO, USH2A, and RPGR. A genetic cause is identified in 50 to 80 percent of cases.

Inheritance

Inheritance patterns vary based on the specific gene involved:

• Autosomal dominant: One copy of the altered gene is sufficient to cause the disorder.
• Autosomal recessive: Both copies of the gene must have a pathogenic variant. Parents typically do not show symptoms.
• X-linked: Genes are located on the X chromosome. Males are typically more severely affected, though at least 20 percent of carrier females may also experience retinal degeneration.
• Digenic: A rare pattern where variants must be present in two different genes.

In 40 to 50 percent of nonsyndromic cases, only one person in a family is affected; these are described as simplex cases, which are often the result of autosomal recessive inheritance.