EYE

Isolated ectopia lentis is a condition that affects the eyes, specifically the positioning of the lens. The lens is a clear structure at the front of the eye that helps focus light. In people with isolated ectopia lentis, the lens in one or both eyes is not centrally positioned as it should be but is off-center (displaced). Isolated ectopia lentis usually becomes apparent in childhood. The lens may drift further off-center over time.

The prevalence of isolated ectopia lentis is unknown. In Denmark, an estimated 6.4 per 100,000 individuals have ectopia lentis, but a large proportion of these cases (about 75 percent) are syndromic.

Mutations in the FBN1 or ADAMTSL4 gene cause isolated ectopia lentis. These genes provide instructions for making proteins that are necessary for the formation of threadlike filaments called microfibrils. Microfibrils provide support to many tissues, including the lenses of the eyes, which are held in position by these filaments.

Mutations in the FBN1 or ADAMTSL4 gene impair protein function and lead to a decrease in microfibril formation or result in the formation of impaired microfibrils. Without functional microfibrils to anchor the lens in its central position at the front of the eye, the lens becomes displaced.

When isolated ectopia lentis is caused by mutations in the FBN1 gene, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

When isolated ectopia lentis is caused by mutations in the ADAMTSL4 gene, it is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Oculocutaneous albinism is a group of conditions that affect coloring (pigmentation) of the skin, hair, and eyes. Affected individuals typically have very fair skin and white or light-colored hair. Long-term sun exposure greatly increases the risk of skin damage and skin cancers, including an aggressive form of skin cancer called melanoma, in people with this condition. Oculocutaneous albinism also reduces pigmentation of the colored part of the eye (the iris) and the light-sensitive tissue at the back of the eye (the retina). People with this condition usually have vision problems such as reduced sharpness; rapid, involuntary eye movements (nystagmus); and increased sensitivity to light (photophobia).

Overall, an estimated 1 in 20,000 people worldwide are born with oculocutaneous albinism. The condition affects people in many ethnic groups and geographical regions.

Oculocutaneous albinism can result from mutations in several genes, including TYR, OCA2, TYRP1, and SLC45A2. Changes in the TYR gene cause type 1; mutations in the OCA2 gene are responsible for type 2; TYRP1 mutations cause type 3; and changes in the SLC45A2 gene result in type 4. Mutations in additional genes likely underlie the other forms of this disorder. The genes associated with oculocutaneous albinism are involved in producing a pigment called melanin, which is the substance that gives skin, hair, and eyes their color. In the retina, melanin also plays a role in normal vision. Mutations in any of these genes disrupt the ability of cells to make melanin, which reduces pigmentation in the skin, hair, and eyes. A lack of melanin in the retina leads to the vision problems characteristic of oculocutaneous albinism.

Oculocutaneous albinism is inherited in an autosomal recessive pattern, which means both copies of a gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they do not show signs and symptoms of the condition.