Leber Congenital Amaurosis
What is Leber Congenital Amaurosis?
Leber congenital amaurosis (LCA) is an inherited retinal degenerative disease characterized by severe loss of vision at birth. A variety of other eye-related abnormalities including roving eye movements, deep-set eyes, and sensitivity to bright light also occur with this disease. Some patients with LCA also experience central nervous system abnormalities.
What are the symptoms?
Individuals with LCA have very reduced vision at birth. Within an infant’s first few months of life, parents usually notice a lack of visual responsiveness and unusual roving eye movements, known as nystagmus. Eye examinations of infants with LCA reveal normal appearing retinas. However, electroretinography (ERG) tests, which measure visual function, detect little if any activity in the retina. A low level of retinal activity, measured by ERG, indicates very little visual function. ERG tests are key to establishing a diagnosis of LCA.
By early adolescence, various changes in the retinas of patients with LCA become readily apparent. Blood vessels often become narrow and constricted. A variety of pigmentary (color) changes can also occur in the retinal pigment epithelium (RPE), the supportive tissue underlying the retina. Sometimes, pigmentary changes are similar to another retinal degenerative disease known as retinitis pigmentosa.
Although the appearance of the retina undergoes marked changes with age, vision usually remains fairly stable through young adult life. Long term visual prognosis remains to be defined. Visual acuity in patients with LCA is usually limited to the level of counting fingers or detecting hand motions or bright lights. Some patients are also extremely sensitive to light (photophobia). Patients with remaining vision are often extremely farsighted.
Many children with LCA habitually press on their eyes with their fists or fingers. This habitual pressing on the eyes is known clinically as oculo-digital reflex. The eyes of individuals with LCA also usually appear sunken or deep set. Keratoconus (cone shape to the front of the eye) and cataracts (clouding of the lens, the clear, glass-like structure through which light passes) have also been reported with this disease.
In some cases, LCA is associated with central nervous system complications such as developmental delay, epilepsy, and motor skill impairment. Because LCA is relatively rare, the frequency of central nervous system complications is unknown.
Is it an inherited disease?
LCA is most typically passed through families by the autosomal recessive pattern of inheritance. In this type of inheritance, both parents, called carriers, have one gene for the disease paired with one normal gene. Each of their children has a 25 percent chance (or 1 chance in 4) of inheriting the two LCA genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene. At this time, it is impossible to determine who is a carrier for LCA until after the birth of an affected child.
Are there any other related diseases?
Initially, LCA can be confused with congenital and hereditary optic atrophy, cortical blindness, congenital stationary night blindness, flecked retina syndrome, and achromatopsia. Although similarly named, LCA should not be confused with Leber optic atrophy. In addition, there are syndromes seen in infancy where visual impairment is a component. A thorough ophthalmologic examination including diagnostic tests measuring retinal function and an accurate documentation of family history can distinguish between these related conditions.
What treatment is available?
Scientists have identified 14 genes with mutations that can each cause LCA. These genes account for approximately 75 percent of all cases of LCA. With this information, scientists are better equipped to develop preventions and treatments.
Clinical trials of gene replacement therapy for LCA caused by mutations in the RPE65 are now underway at Children’s Hospital of Philadelphia, Universities of Pennsylvania and Florida, and Moorfields Eye Hospital at the University College of London. Children and young adults who were nearly blind have had dramatic improvements in their vision after treatment.
This is the same therapy that gave vision to 60 dogs, including the world-famous Lancelot, born blind from LCA. These studies provide great promise for eradicating LCA caused by RPE65, and eventually, LCA caused by other genetic variations.
Some individuals with LCA, who have remaining vision, may also benefit from the use of low-vision aids, including electronic, computer-based and optical aids. Orientation and mobility training, adaptive training skills, job placement, and income assistance are available through community resources.