Four families with the dominant infantile form of optic nerve atrophy

The Pattern of Retinal Ganglion Cell Loss in OPA1-Related Autosomal Dominant Optic Atrophy Inferred From Temporal, Spatial, and Chromatic Sensitivity Losses

Purpose

Progressive retinal ganglion cell (RGC) loss is the pathological hallmark of autosomal dominant optic atrophy (DOA) caused by pathogenic OPA1 mutations. The aim of this study was to conduct an in-depth psychophysical study of the visual losses in DOA and to infer any selective vulnerability of visual pathways subserved by different RGC subtypes.

Methods

We recruited 25 patients carrying pathogenic OPA1 mutations and age-matched healthy individuals. Spatial contrast sensitivity functions (SCSFs) and chromatic contrast sensitivity were quantified, the latter using the Cambridge Colour Test. In 11 patients, long (L) and short (S) wavelength-sensitive cone temporal acuities were measured as a function of target illuminance, and L-cone temporal contrast sensitivity (TCSF) as a function of temporal frequency.

Results

Spatial contrast sensitivity functions were abnormal, with the loss of sensitivity increasing with spatial frequency. Further, the highest L-cone temporal acuity fell on average by 10 Hz and the TCSFs by 0.66 log10 unit. Chromatic thresholds along the protan, deutan, and tritan axes were 8, 9, and 14 times higher than normal, respectively, with losses increasing with age and S-cone temporal acuity showing the most significant age-related decline.

Conclusions

Losses of midget parvocellular, parasol magnocellular, and bistratified koniocellular RGCs could account for the losses of high spatial frequency sensitivity and protan and deutan sensitivities, high temporal frequency sensitivity, and S-cone temporal and tritan sensitivities, respectively. The S-cone-related losses showed a significant deterioration with increasing patient age and could therefore prove useful biomarkers of disease progression in DOA.

A review of primary hereditary optic neuropathies

The primary inherited optic neuropathies are a heterogeneous group of disorders that result in loss of retinal ganglion cells, leading to the clinical appearance of optic atrophy. They affect between 1:10,000 to 1:50,000 people. The main clinical features are a reduction in visual acuity, colour vision abnormalities, centro-caecal visual field defects and pallor of the optic nerve head. Electrophysiological testing shows a normal flash electroretinogram, absent or delayed pattern visually evoked potentials suggestive of a conduction deficit and N95 waveform reduction on the pattern electroretinogram, consistent with a primary ganglion cell pathology. The primary inherited optic neuropathies may be sporadic or familial. The mode of inheritance may be autosomal dominant, autosomal recessive, X-linked recessive or mitochondrial. Within each of these groups, the phenotypic characteristics vary in such features as the mode and age of onset, the severity of the visual loss, the colour deficit and the overall prognosis. A number of different genes (most as yet unidentified) in both nuclear and mitochondrial genomes, underlie these disorders. The elucidation of the role of the encoded proteins will improve our understanding of basic mechanisms of ganglion cell development, physiology and metabolism and further our understanding of the pathophysiology of optic nerve disease. It will also improve diagnosis, counselling and management of patients, and eventually lead to the development of new therapeutic modalities.

Optic disc morphology of patients with OPA1 autosomal dominant optic atrophy

BACKGROUND/AIMS

Patients with autosomal dominant optic atrophy (ADOA) are genetically heterogeneous, but all have disc pallor. A degree of cupping in ADOA can make the distinction from normal tension glaucoma (NTG) clinically difficult. This study aimed to clarify the features of the optic nerve of patients with ADOA at the OPA1 locus.

METHODS

29 patients (58 eyes), from 12 families, were identified in a prospective observational study of patients with ADOA examined by a single observer between 1995 and 1998, in whom genetic analysis showed either evidence for linkage to chromosome 3q28 or mutations in the ADOA gene, OPA1. All of the patients had disc and fundal photographs available for retrospective analysis. Clinical data collected included disc appearance, intraocular pressure, Snellen visual acuity, Hardy-Rand-Rittler colour vision plates, and Humphrey 30-2 visual fields.

RESULTS

Mean age at time of examination was 37 years and mean visual acuity was 6/24. Disc morphology showed temporal disc pallor in 30 eyes (52%) and total disc pallor in 28 eyes (48%). At least one disc showed a cup to disc ratio of more than 0.5 in 18 patients (28 discs, 48%). The temporal neuroretinal rim always showed pallor and shallow shelving (or saucerisation) was seen in 46 eyes (79%). Only 12 discs (21%) had deep excavation and baring of blood vessels. All of the patients had normal intraocular pressure and no family history of glaucoma. There was a temporal grey, pigmentary crescent in 12 patients (18 eyes, 31%) and peripapillary atrophy in 20 patients (40 eyes, 69%), but disc margin haemorrhages were not seen. There was no maculopathy or retinopathy.

CONCLUSION

The optic disc morphology, described for the first time in this genetically homogeneous population of patients with OPA1 ADOA, shows a distinctive absence of a healthy neuroretinal rim and shallow saucerisation of the optic disc cup, with frequent peripapillary atrophy.

Disc excavation in dominant optic atrophy: differentiation from normal tension glaucoma

OBJECTIVE

In patients with dominant optic atrophy (DOA, Kjer type), excavation of the optic nerve develops, and these patients may be misdiagnosed as having normal tension glaucoma (NTG). This study examined disc morphologic features in patients with DOA and explored features that help distinguish this condition from NTG.

DESIGN

Noncomparative, observational case series.

PARTICIPANTS

Patients with DOA who were seen at the Duke University Eye Center between 1987 and 1996 and who had bilateral optic nerve photographs.

METHODS

Retrospective chart review of the results of visual acuity testing, visual field testing by Goldmann perimetry, color vision testing, intraocular pressure measurement, and observation of bilateral optic nerve photographs.

MAIN OUTCOME MEASURES

Appearance of the optic disc and peripapillary zone in patients with DOA.

RESULTS

Nine patients were identified. The mean age at the time of evaluation was 28 years (range, 11-62 years). Most patients had a mild to moderate reduction in visual acuity. Color vision as tested with Hardy-Rand-Rittler plates was reduced (4.0/10 +/- 4.2/10). A cup-to-disc ratio of more than 0.5 was observed in at least one eye of eight patients. A temporal wedge-shaped area of excavation was observed in 14 of the 18 eyes studied. Moderate to severe temporal pallor was observed in all of the eyes. Pallor of the remaining (noncupped) neuroretinal rim was also observed consistently, ranging from mild to moderate. A gray crescent and some degree of peripapillary atrophy were noted in all eyes.

CONCLUSIONS

Several clinical features, including early age of onset, preferential loss of central vision, sparing of the peripheral fields, pallor of the remaining neuroretinal rim, and a family history of unexplained visual loss or optic atrophy, help to distinguish patients with DOA from those with NTG.

Clinical features, molecular genetics, and pathophysiology of dominant optic atrophy

Inherited optic neuropathies are a significant cause of childhood and adult blindness and dominant optic atrophy (DOA) is the most common form of autosomally inherited (non-glaucomatous) optic neuropathy. Patients with DOA present with an insidious onset of bilateral visual loss and they characteristically have temporal optic nerve pallor, centrocaecal visual field scotoma, and a colour vision deficit, which is frequently blue-yellow. Evidence from histological and electrophysiological studies suggests that the pathology is confined to the retinal ganglion cell. A gene for dominant optic atrophy (OPA1) has been mapped to chromosome 3q28-qter, and studies are under way to refine the genetic interval in which the gene lies, to map the region physically, and hence to clone the gene. A second locus for dominant optic atrophy has recently been shown to map to chromosome 18q12.2-12.3 near the Kidd blood group locus. The cloning of genes for dominant optic atrophy will provide important insights into the pathophysiology of the retinal ganglion cell in health and disease. These insights may prove to be of great value in the understanding of other primary ganglion cell diseases, such as the mitochondrially inherited Leber's hereditary optic neuropathy and other diseases associated with ganglion cell loss, such as glaucoma.

A gene for X-linked optic atrophy is closely linked to the Xp11.4-Xp11.2 region of the X chromosome

The aim of this study was to identify the chromosomal location of the disease-causing gene in a family apparently segregating X-linked optic atrophy. A large family of 45 individuals with a four-generation history of X-linked optic atrophy was reexamined in a full ophthalmic as well as electrophysiological examination. A DNA linkage analysis of the family was undertaken in order to identify the chromosomal location of the disease-causing gene. Linkage analysis was performed with 26 markers that spanned the entire X chromosome. The affected males showed very early onset and slow progression of the disease. Ophthalmic study of the female carriers did not reveal any abnormalities. Close linkage without recombination was found at the MAOB locus (maximum LOD score [Zmax] 4.19). The Zmax - 1 support interval was found at a recombination fraction of .076 distal and .018 proximal to MAOB. Multipoint linkage analysis placed the optic atrophy-causing gene in the Xp11.4-p11.21 interval between markers DXS993 and DXS991, whereas any other localization along the X chromosome could be excluded.

Histopathology of eye, optic nerve and brain in a case of dominant optic atrophy

Histopathology of eye, optic nerve and brain was performed in a patient with typical signs and symptoms of dominant optic atrophy. He belonged to a previously-reported family of 152 members in which optic atrophy was demonstrable in 14 persons, and probably present in a further 8 cases. In the eyes, fibrosis of the retinal ganglion cell layer and disc was found. Ultrastructural examination showed a few remaining cells in this layer, heavy fibrosis and in particular a highly condensed inner limiting membrane. The optic nerves, the optic chiasm and optic tracts showed an increased content of collagen tissue and a decreased number of neurofibrils and myelin sheaths. In the lateral geniculate body there was massive loss of ganglion cells, fibrillary gliosis and a great quantity of fine granular lipid in the cytoplasm of the ganglion cells. No changes in the calcarine cortex were observed. Examination of the intracranial part of both vestibulocochlear nerves showed a decreased number of neurofibrils and myelin sheaths. It is concluded that the histopathological changes of the visual system are similar to those in Leber's disease, but less pronounced. The study confirms earlier theories that dominant optic atrophy is a primary degeneration of the ganglion cell layer in the retina, with ascending optic atrophy.

Autosomal dominant optic atrophy. A spectrum of disability

Autosomal dominant optic atrophy is an abiotrophy with an insidious onset in the first decade of life. The clinical features of 31 individuals in six pedigrees are detailed in this study. These data suggest that here is considerable intrafamilial and interfamilial expression of dysfunction. Moreover, asymmetry of the visual loss in not unusual. An unexpected result of this study is the previously unreported frequent association of a neural hearing loss with this disorder.

A clinicopathologic study of autosomal dominant optic atrophy

Of a family with 40 members, 12 had autosomal dominant optic atrophy. The affected members were aware of reduced vision from the first decade. Visual loss was moderate to severe, 6/12 (20/40) to 3/60 (10/200). The affected members showed similar centrocecal scotomata. Most affected patients had severe unclassified color defects. Electroretinography measurements were normal in all but one patient who had a small reduction in the scotopic response. The pathologic changes in a patient with autosomal dominant optic atrophy showed diffuse atrophy of the ganglion cell layer of the retina with a loss of myelin and nerve tissue within the optic nerves. We suggest that autosomal dominant atrophy is a primary degeneration of retinal ganglion cells.