Dominant optic atrophy, or dominant optic atrophy, Kjer's type, is an autosomally inherited disease that affects the optic nerves, causing reduced visual acuity and blindness beginning in childhood. This condition is due to mitochondrial dysfunction mediating the death of optic nerve fibers. Dominant optic atrophy was first described clinically by Batten in 1896 and named Kjer’s optic neuropathy in 1959 after Danish ophthalmologist Poul Kjer, who studied 19 families with the disease. Although dominant optic atrophy is the most common autosomally inherited optic neuropathy aside from glaucoma, it is often misdiagnosed.
Presentation
Autosomal dominant optic atrophy can present clinically as an isolated bilateral optic neuropathy or rather as a complicated phenotype with extra-ocular signs. Dominant optic atrophy usually affects both eyes roughly symmetrically in a slowly progressive pattern of vision loss beginning in childhood and is hence a contributor to childhood blindness. Vision testing will reveal scotomas in the central visual fields with peripheral vision sparing and impaired color vision. Visual acuity loss varies from mild to severe, typically ranging from 6/6 to 6/60 with a median value of 6/36, corrected vision. In rare cases, vision loss is more severe. Characteristic changes of the fundus evident on examination is temporal pallor of the optic disc and in its end stage, excavation of the optic disc, as is also seen in Leber hereditary optic neuropathy and normal tension glaucoma. Because the onset of Dominant optic atrophy is insidious, symptoms are often not noticed by the patients in its early stages and are picked up by chance in routine school eye screenings. First signs of Kjer's typically present between 4–6 years of age, though presentation at as early as 1 year of age has been reported. In some cases, Dominant optic atrophy may remain subclinical until early adulthood. Progression of dominant optic atrophy varies even within the same family. Some have mild cases with visual acuity stabilizing in adolescence, others have slowly but constantly progressing cases, and others still have sudden step-like decreases in visual acuity. Generally, the severity of the condition by adolescence reflects the overall level of visual function to be expected throughout most of the patient’s adult life. Slow decline in acuity is known to occur in late middle age in some families. In complicated cases of autosomal dominant optic atrophy, in addition to bilateral optic neuropathy, several other neurological signs of neurological involvement can be observed: peripheral neuropathy, deafness, cerebellar ataxia, spastic paraparesis, myopathy.
Genetics
Dominant optic atrophy is inherited in an autosomal dominant manner. That is, a heterozygous patient with the disease has a 50% chance of passing on the disease to offspring, assuming his/her partner does not have the disease. Males and females are affected at the same rate. Although Kjer's has a high penetrance, severity and progression of DOA are extremely variable even within the same family.
Pathophysiology
Vision loss in dominant optic atrophy is due to optic nerve fiber loss from mitochondria dysfunction. Dominant optic atrophy is associated with mutation of the OPA1 gene found on chromosome 3, region q28-qter. Also, 5 other chromosomal genes are described as causing optic atrophy: OPA2, OPA3, OPA4, OPA5 and OPA6 . The OPA1 gene codes for a dynamin-related GTPase protein targeted to the mitochondrial inner membrane. OPA1 has distinct roles in the fusion of mitochondrial inner membranes during mitochondrial fusion events, and in regulation of cell death. Mitochondria are subcellular structures that generate and transform energy from metabolism into discrete usable units for the cell’s functions. Retinal ganglion cells, which make up the optic nerve, have a high energy demand and are particularly sensitive to mitochondrial dysfunction. This is especially the case for smaller and less myelinated neurons such as those found in the papillomacular bundle of the retina, which transmit information corresponding to the central visual field. Biochemical and mitochondrial morphological studies on cells from patients affected by autosomal dominant optic atrophy have shown a severe defect in the shape and distribution of mitochondria, occurring independently from a bioenergetic defect or apoptosis, indicating that the mitochondrial fusion defect is the primary pathogenetic mechanism, although variable bioenergetic defects can also occur as a secondary phenomenon, especially in severe cases with complicated phenotypes and accumulation of multiple mitochondrial-DNA deletions. Over 60 different mutations of the OPA1 gene causing Kjer's have been reported, most of which occur in the catalytic domain of the protein. Mutations at the OPA1 gene are also associated with normal tension glaucoma and deafness.
Management
Currently there is no effective therapy for dominant optic atrophy, and consequently, these patients are simply monitored for changes in vision by their eye-care professional. Children of patients should be screened regularly for visual changes related to dominant optic atrophy. Research is underway to further characterize the disease so that therapies may be developed. Since November 2018, has been focusing on fellow patients and their families. They have the following goals: scientific research, disease awareness, interaction between all parties involved and a trustworthy place for the patients.
Incidence
The incidence of dominant optic atrophy has been estimated to be 1:50000 with prevalence as high as 1:10000 in the Danish population.
