Clinical heterogeneity of dominant optic atrophy: the contribution of visual function investigations to diagnosis

Inherited mitochondrial optic neuropathies

Leber hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (DOA) are the two most common inherited optic neuropathies and they result in significant visual morbidity among young adults. Both disorders are the result of mitochondrial dysfunction: LHON from primary mitochondrial DNA (mtDNA) mutations affecting the respiratory chain complexes; and the majority of DOA families have mutations in the OPA1 gene, which codes for an inner mitochondrial membrane protein critical for mtDNA maintenance and oxidative phosphorylation. Additional genetic and environmental factors modulate the penetrance of LHON, and the same is likely to be the case for DOA which has a markedly variable clinical phenotype. The selective vulnerability of retinal ganglion cells (RGCs) is a key pathological feature and understanding the fundamental mechanisms that underlie RGC loss in these disorders is a prerequisite for the development of effective therapeutic strategies which are currently limited.

Dominant optic atrophy: correlation between clinical and molecular genetic studies

PURPOSE

To assess the clinical picture and molecular genetics of 14 Finnish families with dominant optic atrophy (DOA).

METHODS

The clinical status of family members was based on the assessment of visual acuity, colour vision, visual fields and optic nerve appearance; 31 individuals were affected, two suspect and 21 unaffected. A total of 30 coding exons and exon- intron boundaries of the OPA1 gene were sequenced in order to detect mutations.

RESULTS

Half the patients were diagnosed at the age of < or = 20 years. Ten out of 20 affected individuals followed up for > or = 6 years had a progressive disease and 10 had a stable disease. According to WHO criteria, 36% of the affected patients were visually handicapped. Eight OPA1 pathogenic mutations, all but one novel, and 18 neutral polymorphisms were detected.

CONCLUSION

The most sensitive indicators of DOA were optic disc pallor and dyschromatopsia. With molecular genetic analysis, asymptomatic mutation carriers and DOA cases with a mild clinical outcome were ascertained. No mutational hotspot or Finnish major mutation in the OPA1 gene could be demonstrated as most families carried a unique mutation. No obvious genotype- phenotype correlation could be detected. Detailed clinical assessment and exclusion of non-DOA families prior to mutation screening are necessary for obtaining a high mutation detection rate.

Hereditary optic neuropathies

AIMS

To provide a clinical update on the hereditary optic neuropathies.

METHODS

Review of the literature.

RESULTS

The hereditary optic neuropathies comprise a group of disorders in which the cause of optic nerve dysfunction appears to be hereditable, based on familial expression or genetic analysis. In some hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. In others, various neurologic and systemic abnormalities are regularly observed.

CONCLUSION

The most common hereditary optic neuropathies are autosomal dominant optic atrophy (Kjer's disease) and maternally inherited Leber's hereditary optic neuropathy. We review the clinical phenotypes of these and other inherited disorders with optic nerve involvement.

Dominant optic atrophy. Refining the clinical diagnostic criteria in light of genetic linkage studies

OBJECTIVE

To describe the clinical findings and refine the clinical diagnostic criteria for dominant optic atrophy based on eight British families in which the diagnosis was confirmed by linkage analysis.

DESIGN AND PARTICIPANTS

Case series; 92 subjects in 8 pedigrees had both eyes examined.

INTERVENTION

Family members received a domiciliary examination based on best-corrected visual acuity, color vision using Ishihara and Hardy Richter Rand (HRR) plates, confrontation field testing using a red target, and optic disc evaluation using a direct ophthalmoscope. Genomic DNA was extracted from leukocytes or buccal mucosal cells and genotyped using 12 fluorescently labeled microsatellite markers from the region 3q27-q29.

MAIN OUTCOME MEASURES

Subjects were classified clinically as definitely or possibly affected on the basis of the domiciliary examination before genetic analysis, and these results were compared with the haplotype analysis.

RESULTS

Clinically, 43 subjects were identified as definitely affected, 4 as possibly affected, and 45 as unaffected. Visual acuity in affected subjects ranged from 6/6 to count fingers and declined with age. On genetic analysis, a haplotype was identified in each family, which was found in all definitely affected members but not in those regarded as unaffected. The four possibly affected individuals also bore the haplotype that segregated with the disease.

CONCLUSIONS

Simple clinical tests are highly efficacious in diagnosing dominant optic atrophy. Contrary to accepted criteria, symptoms begin before the age of 10 years in only 58% of affected individuals. Visual acuity in affected subjects is highly variable. A mild degree of temporal or diffuse pallor of the optic disc and minimal color vision defects, in the context of a family with dominant optic atrophy, are highly suggestive of an individual being affected, even if the visual acuity is normal. This widens the generally accepted diagnostic criteria for this disease.

Autosomal-dominant retinitis pigmentosa associated with an Arg-135-Trp point mutation of the rhodopsin gene. Clinical features and longitudinal observations

PURPOSE

To report the clinical and functional characteristics of patients affected with autosomal-dominant transmitted retinitis pigmentosa (adRP) from a large Italian pedigree in which a point mutation predicting the Arg-135-Trp change of rhodopsin was identified by polymerase chain reaction-single-strand conformation polymorphism analysis.

METHODS

Seven patients, ranging in age from 6 to 41 years, underwent a full clinical ophthalmologic evaluation, kinetic visual field testing, and electroretinographic testing.

RESULTS

In agreement with previous reports, this rhodopsin mutation yielded a particularly severe phenotype, both clinically and functionally. The evaluation of patients from this pedigree in the first and second decade of life demonstrated that retinal function is still electroretinographically measurable at least until 18 years of age, although reduced to 2% to 4% of normal. Longitudinal measures showed that the rate of progression of the disease was unusually high, with an average 50% loss per year of electroretinographic amplitude and visual field area with respect to baseline. Later in the course of the disease, macular function is also severely compromised, leaving only residual central vision by the fourth decade of life.

CONCLUSIONS

The phenotype associated with mutations in codon 135 of the rhodopsin molecule appears to have an unusually high progression rate and yields an extremely poor prognosis. These distinctive features make the Arg-135-Trp phenotype substantially different from the general RP population, and also from many of the other adRP pedigrees with known rhodopsin mutations reported to date.