Albinism ocular late onset sensorineural deafness

Synonyms

8

Overview

Ocular albinism (OA) is a genetic condition that primarily affects the eyes and it occurs almost exclusively in males, is a gene mutation on the X chromosome. This condition reduces the coloring (pigmentation) of the iris, which is the colored part of the eye, and the retina, which is the light-sensitive tissue at the back of the eye. Pigmentation in the eye is essential for normal vision.

Ocular albinism is characterized by severely impaired sharpness of vision (visual acuity) and problems with combining vision from both eyes to perceive depth (stereoscopic vision). Although the vision loss is permanent, it does not worsen over time. Other eye abnormalities associated with this condition include rapid, involuntary eye movements (nystagmus); eyes that do not look in the same direction (strabismus); and increased sensitivity to light (photophobia). Many affected individuals also have abnormalities involving the optic nerves, which carry visual information from the eye to the brain.

Unlike some other forms of albinism, ocular albinism does not significantly affect the color of the skin and hair. People with this condition may have a somewhat lighter complexion than other members of their family, but these differences are usually minor.
The most common form of ocular albinism is known as the Nettleship-Falls type or type 1. Other forms of ocular albinism are much rarer and may be associated with additional signs and symptoms, such as hearing loss.

There are multiple forms of ocular albinism, which are clinically similar. Ocular albinism is inherited in two patterns, X-linked and autosomal pattern. X-linked OA includes type I OA (Nettership-Falls type), type II OA (Forsius-Eriksson type), and OA with late-onset sensorineural deafness. 

Ocular albinism, type 1 (OA1):

Also known as Nettleship-Falls syndrome, is the most common variety of ocular albinism. OA1 is usually associated with nystagmus, and difficult to otherwise detect in females; males show more readily observable symptoms.

Ocular albinism, type 2 (OA2):

Also known as Forsius-Eriksson syndrome or "Åland Island eye disease", mostly affects males, though females are often carriers and can sometimes be symptomatic; it is frequently linked with protanopic dichromacy (a form of color blindness) and with night blindness (nyctalopia).

Ocular albinism with sensorineural deafness (OASD):

It is, as its name implies, associated with loss of hearing. May be the same as OA1.

Symptoms

  • Deafness
  • Pigmented nevi
  • Freckles
  • Skin neoplasia
  • Rapid involuntary eye movements
  • Reduced visual acuity
  • Ocular albinism
  • Photophobia
  • Reduced coloring of the iris and retina (ocular hypopigmentation)
  • Foveal hypoplasia (underdevelopment)
  • Rapid, involuntary eye movements (nystagmus)
  • Poor vision
  • Poor depth perception
  • Eyes that do not look in the same direction (strabismus)
  • Increased sensitivity to light
  • Nystagmus
  • Sensorineural hearing impairment
  • Visual impairment

Causes

It is caused by mutations in the GPR143 gene and is inherited in an X-linked recessive manner. Females have been affected in rare instances. This gene provides instructions for making a protein that plays a role in pigmentation of the eyes and skin. It helps control the growth of melanosomes, which are cellular structures that produce and store a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color. In the retina, this pigment also plays a role in normal vision. Mutations in the GPR143 gene can affect the protein's ability to do its job. As a result, melanosomes in skin and retinal cells can grow abnormally large, contributing to the signs and symptoms of the condition. In rare cases, the genetic cause of this condition is unknown.

Diagnosis

The diagnosis of ocular albinism is based on the characteristic eye findings. Female relatives who carry the gene for ocular albinism will have some retinal pigment abnormalities (seen as mild iris transillumination) but usually will not have the visual changes observed in affected males. Very rarely females can be affected with the hallmarks of OA1 including nystagmus and foveal hypoplasia with reduced visual acuity. Molecular genetic testing for GPR143 gene detects mutations in approximately 90% of affected males and is available to confirm the diagnosis.

Treatment

Individuals diagnosed with ocular albinism should be evaluated by an ophthalmologist at the time of diagnosis to determine the extent of the disease and have ongoing ophthalmologic examinations annually. Glasses or contact lenses can greatly improve vision. Dark glasses or a hat with a brim can help to reduce sun sensitivity (photophobia).

Resources

  • NIH