Aland eye disease: Description, Causes and Risk Factors:
Aland eye disease (AED) is an X-linked recessive retinal disease characterized by fundus hypopigmentation, decreased visual acuity, nystagmus, astigmatism
, progressive axial myopia, defective dark adaptation and protanopia. AED is a very rare disease originally reported in a family from Aland islands in the Bothnia sea. Some other cases from the Baltic area and other origins have been reported but the clinical features of these cases overlap with X-linked incomplete congenital stationary night blindness CSNB2 (Congenital Stationary Night Blindness Type 2). Aland eye disease is characterized by hypopigmented eye fundus, foveal dysplasia with no foveal reflex that leads to decreased visual acuity, progressive axial myopia, latent nystagmus, astigmatism, night blindness and protan color vision defect. The hypopigmentation is most pronounced in the posterior pole and in the peripapillary region. Female carriers may show slight disturbances of color discrimination and subtle nystagmus. Aland eye disease is caused by mutations in the CACNA1F gene. Some mutations in CACNA1F are associated with CSNB2 suggesting allelism of the two disorders.
This is an X-linked disorder resulting from a mutation in the CACNA1F gene located at Xp11.23. Molecular DNA studies suggest that there may be some heterogeneity in the causative mutations but in the original family reported by Forsius and Eriksson, a 425-bp deletion in the CACNA1F gene has been found to segregate as expected in the phenotypes. The highly variable and subtle nature of clinical manifestations in females limits their usefulness in determination of carrier status and genotyping is necessary.
The CSNB2A type of congenital stationary night blindness caused by mutations in the same gene suggesting allelism of the two disorders. Aland Island eye disease shares some clinical features such as night blindness and occasionally mild color vision defects but differs in the presence of progressive myopia and an abnormal fovea.
Clinical and molecular genetic studies were performed on a single, large, white family, in which congenital nystagmus and moderate to high refractive error segregated as a sex linked trait with manifestation in some female carriers. In this family, affected males demonstrate myopia, but a high proportion of female carriers, and some of the possibly affected males, show hypermetropia. Clinical ophthalmic examination and electrodiagnostic studies of retinal function were fully compatible with a diagnosis of either incomplete congenital stationary night blindness or of Aland island eye disease. Previous studies have mapped both disorders to the proximal short arm of the X chromosome: our molecular studies support this localisation. Incomplete congenital stationary nightblindness and Aland Island eye disease could be considered as a single entity.
Individuals with active AED have astigmatism, diminished visual acuity
, foveal hypoplasia (slow response to changes in light), fundus hypopigmentation (very pale whites of the eyes), poor red-green color vision, progressive myopia (nearsightedness), nystagmus (rapidly moving eyes), and stationary night blindness. Nystagmus can be induced in women with the gene for AIED.
Differential diagnosis includes X-linked ocular albinism (OA1) and CSNB2. The lack of misrouting of optic nerve axons excludes OA1 whereas CSNB2 is apparently stationary with a normal fovea and, usually, no color defects. Aland eye disease is an X-linked disorder, with a carrier female having a 50% chance of transmitting the mutation to her offspring. Carrier testing for atrisk female relatives is possible. Genetic counseling of the family is recommended.
Patients with a clinical suspicion of AED should undergo a complete ophthalmologic examination including funduscopy, visual acuity, refraction defects, electroretinogram (ERG) and color vision test. Mutation screening of CACNA1F gene including the presence of large deletions in the gene can help the clinical diagnosis.
No treatment is available except for correction of the myopia. Except for progression ofaxial myopia, the disease presents a stationary course.
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