Congenital amaurosis of retinal origin (Leber)

A novel syndrome of congenital lid and punctal anomalies, corneal and chorioretinal dystrophy

A 28-year old woman had an ocular syndrome consisting of congenital lid and punctal anomalies, and corneal and chorioretinal dystrophy without facial dysmorphism. These combined malformations of the ocular adnexae and both anterior and posterior ocular segments have not been previously described and appear to represent a novel syndrome. Direct sequencing of PAX6 and the DNA-binding domain of FOXC1 failed to detect a mutation.

Leber's congenital amaurosis: an update

Leber's congenital amaurosis (LCA) is a clinically and genetically heterogeneous disorder characterized by severe loss of vision at birth. It accounts for 10-18% of cases of congenital blindness. Some patients exhibit only blindness of retinal origin whereas others show evidence of a multi-systemic involvement. We review the literature relating to this severe disorder, highlighting unresolved questions, in particular the nature of the association of LCA with mental retardation and with systemic findings and syndromic pictures. In recent years, genetic advances in the diagnosis of LCA have opened up new horizons, also from a therapeutic point of view. A better understanding of this pathology would be valuable for paediatric neurologists.

Molecular aspects of retinal degenerative diseases

Retinal degeneration, either acquired or inherited, is a major cause of visual impairment and blindness in humans. Inherited retinal degeneration comprises a large group of diseases that result in the loss of photoreceptor cells. To date, 131 retinal disease loci have been identified, and 76 of the genes at these loci have been isolated (RetNet Web site). Several of these genes were first considered candidates because of their chromosomal localization or homology to genes involved in retinal degeneration in other organisms. In this review, I will discuss recent advances in the identification of genes that cause retinal degeneration, and I will describe the mechanisms of photoreceptor death and potential treatments for retinal degenerative diseases.

Ocular colobomata

Ocular colobomata present diagnostic and therapeutic challenges in patients of all ages, but especially in young children. The "typical" coloboma, caused by defective closure of the fetal fissure, is located in the inferonasal quadrant, and it may affect any part of the globe traversed by the fissure from the iris to the optic nerve. Ocular colobomata are often associated with microphthalmia, and they may be idiopathic or associated with various syndromes. Types and severity of complications vary depending on the location and size of the colobomata. This article reviews the pathogeneses, categorization, genetic bases, differential diagnoses and management of ocular coloboma.

Recurrent keratoconus in a patient with Leber congenital amaurosis

PURPOSE

Clinical history of a 17-year-old patient with Leber congenital amaurosis (LCA) with histologically proven recurrent keratoconus (KC) two years after corneal transplantation in one eye and a recurrence-like appearance with a more global contour on the other eye four years after corneal grafting is reported. The possible mechanisms for this recurrence are discussed in light of the fact that this is, to the best of our knowledge, the first penetrating keratoplasty reported in LCA.

METHODS

Computerized videokeratography (CVKG) and specular microscopy were performed preoperatively. The patient underwent regrafting, and the excised corneal button was examined by light microscopy and transmission electron microscopy.

RESULTS

Analysis of CVKG showed a keratoconus-like pattern on the right eye, with the left eye demonstrating the aspects usually seen in keratoglobus. Histologic examination revealed the features usually observed in progressed keratoconus.

CONCLUSION

Recurrence of keratoconus in a graft has not yet been described after such a short time until now. A "true" recurrence of the disease is postulated; it could be caused by an "aggressive" genetic factor that also leads to the frequent KC in patients with LCA. This mechanism also could explain the high incidence and rapid progress of KC in this disease.

Leber congenital amaurosis

Leber's congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies responsible for congenital blindness. Genetic heterogeneity of LCA has been suspected since the report by Waardenburg of normal children born to affected parents. In 1995, we localized the first disease causing gene, LCA1, to chromosome 17p13 and confirmed the genetic heterogeneity. In 1996, we ascribed LCA1 to mutations in the photoreceptor-specific guanylate cyclase gene (retGC1). RetGC1 is an essential protein implicated in the phototransduction cascade, especially in the recovery of the dark state after the excitation process of photoreceptor cells by light stimulation. In 1997, mutations in a second gene were reported in LCA, the RPE65 gene, which is the first specific retinal pigment epithelium gene. The protein RPE65 is implicated in the metabolism of vitamin A, the precursor of the photoexcitable retinal pigment (rhodopsin). Finally, a third gene, CRX, implicated in photoreceptor development, has been suspected of causing a few cases of LCA. Taken together, these three genes account for only 27% of LCA cases in our series. The three genes encode proteins that are involved in completely different physiopathologic pathways. Based on these striking differences of physiopathologic processes, we reexamined all clinical physiopathological discrepancies and the results strongly suggested that retGC1 gene mutations are responsible for congenital stationary severe cone-rod dystrophy, while RPE65 gene mutations are responsible for congenital severe but progressive rod-cone dystrophy. It is of tremendous importance to confirm and to refine these genotype-phenotype correlations on a large scale in order to anticipate the final outcome in a blind infant, on the one hand, and to further guide genetic studies in older patients on the other hand.

The natural history of Leber's congenital amaurosis. Age-related findings in 35 patients

The authors studied 35 patients with Leber's congenital amaurosis and assessed visual acuity, fundus appearance, and systemic findings. The patients were arbitrarily divided into five age groups. Visual acuities were comparable at all ages. Of 22 patients seen for follow-up examinations (mean length of follow-up, 5 years), vision worsened slightly in only 4 patients (3 with macular coloboma-like lesions and 1 with keratoconus). Fifty percent of retinal examinations in patients younger than 1 year of age were normal. With increasing age, retinal pigmentary changes became evident. All but four patients seen on more than one occasion developed progressive retinal/retinal pigment epithelium changes. Cataracts (5 patients) and keratoconus (3 patients) were present only in older patients (9 to 33 years of age). In Leber's congenital amaurosis, which probably comprises a number of genetically heterogenous conditions, visual acuity remains stable despite progressive retinal pigmentary changes. The subgroup of patients with macular colobomas, however, may develop progressive decrease in vision. Cataracts and keratoconus are additional factors contributing to visual impairment in older patients.

Linkage studies and mutation analysis of the PDEB gene in 23 families with Leber congenital amaurosis

The phenotype in the rd mouse is similar to the clinical presentation of Leber congenital amaurosis (LCA) in humans. Recently a nonsense mutation in the beta subunit of the cGMP phosphodiesterase (Pdeb) gene has been defined as the cause for the rd phenotype in the mouse and has raised the question as to whether mutations in the human PDEB gene might cause LCA. We have previously cloned and characterized the human homologue of the mouse Pdeb gene and have mapped it to chromosome 4p16.3. In this study, a total of 23 LCA families of various ethnic backgrounds have been investigated. Linkage analysis using highly polymorphic (CA)n microsatellites has excluded the PDEB gene as a cause for LCA in 6 families. In the remaining 17 families, we have searched for mutations in the 22 exons of the PDEB gene using single-strand gel electrophoresis (SSGE). Multiple exonic polymorphisms have been determined. However, no DNA changes in the PDEB gene have been identified in our study population which could be causative for the LCA phenotype.

Clinical spectrum of leber's congenital amaurosis in the second to fourth decades of life

Leber's congenital amaurosis is a type of congenital retinitis pigmentosa in which the fundus abnormalities are extremely variable and to some extent age dependent. Most cases are seen in infancy. The retinal, electroretinogram, and fluorescein angiographic findings are described in ten patients with Leber's congenital amaurosis who ranged in age from 13 to 36 years when first seen. All of the patients were from Honduras and were unrelated except for one pair (a brother and sister). The polymorphic appearance of the fundus is emphasized and is particularly striking in the siblings. A macular lesion (a bull's-eye maculopathy) not previously associated with Leber's congenital amaurosis is reported as a variant fundus appearance in this entity.

The infant with nystagmus, normal appearing fundi, but an abnormal ERG

Many retinal disorders present during infancy with nystagmus, decreased vision, and normal-appearing fundi, but an abnormal ERG. The most common of these disorders are Leber's congenital amaurosis, achromatopsia, and congenital stationary night-blindness. Other disorders with similar ocular manifestations may be associated with a variety of life-threatening systemic abnormalities. This review describes the clinical, electrophysiological, and laboratory findings that can be used to distinguish among these conditions.

Leber's congenital amaurosis--a new syndrome with a cardiomyopathy

Seven members of four families had nystagmus noted by 4 months of age, poor vision, photophobia, and a markedly reduced or absent electroretinogram. Six of these patients had a life threatening episode of cardiac failure in infancy. There were also two neonatal deaths, and one of the affected children died at 2 years and one at 19 years. The five surviving children are well, remain with nystagmus, and have visual acuities of less than 6/60, with the eldest two having lost perception of light. They have a short obese habitus distinct from that of their unaffected siblings and parents.

Retinal dystrophy and macular coloboma

Seven cases of retinal dystrophy associated with bilateral macular colobomata are presented. Two separate entities were found. The first is a congenital onset pigmentary retinopathy similar in electrophysiologic findings and symptoms to typical Leber's congenital amaurosis; the second appears to be a form of pregressive cone-rod dystrophy with pigmentary retinopathy. Review of the pertinant literature and clinical evidence suggest that both conditions are distinct entities inherited in the autosomal recessive manner.

Yellowish flecks in Leber's congenital amaurosis

The fundus abnormalities of Leber's congenital amaurosis are extremely variable, from normal to salt-and-pepper changes to typical retinitis pigmentosa. A less commonly seen appearance is that of multiple, irregular shaped, yellowish white flecks deep in the midperipheral retina in a periarteriolar distribution. The nasal fundus as well as the posterior pole are spared. Such a case is presented along with a four-year follow-up together with the fluorescein angiographic findings. The flecks appear to be specific for this entity.

Macular colobomas in Leber's congenital amaurosis

Two siblings with Leber's congenital amaurosis had the unusual association of bilateral macular colobomas. In addition to the colobomas, the patients also had deafmutism, severe myopia, large corneas, and an unusual discrete area of peripapillary tapetoretinal sheen. Electrodiagnostic evaluation of patients with congenitally poor visual ascuity and a central retinal defect differentiated a localized loss of funciton from a degeneration involving the entire retina.

Retinitis pigmentosa

The authors review the symptomatic and genetic aspects of the various entities of isolated retinitis pigmentosa (R.P), both in its typical form and in the forms associated with the affection of other ocular tissues. Syndromes in which R. P. is associated with the affection of other organs and systemic disorders are also cconsidered. Origin, diagnosis and the course of the disease are discussed with regard to electrophysiology, histopathology, fluorescein angiography and biochemistry. Animal research has provided new realizations about the ultrastructure and physiological mechanisms of retinal photoreceptors, and better understanding of abnormal changes. The possible pathogenesis of the human disease, based on research findings, is onsidered. Although R.P. is generally thought to be to be an "untreatable" disease, therapy may be effective in several pathological entities. Methods and results of therapy with vitamins, light deprivation and vision aids are discussed.

Disc oedema in congenital amaurosis of Leber

Images