Arteriovenous communications of the retina

BACKGROUND

Arteriovenous communications of the retina (AVCR) is a rare, congenital, retinal vascular anomaly. Usually it is unilateral, with a predilection for the papillomacular area and superotemporal quadrant of the retina. Men and women are equally affected, and rarely is this condition inherited.

METHODS

A 32-year-old woman was examined with complaints of blurred vision in the left eye after viewing a solar eclipse through a telescope. A complete eye examination showed no visible damage from viewing the eclipse, but a suspected AVCR in the left retina was observed. The patient was referred to a retina specialist for further evaluation.

RESULTS

The patient was diagnosed with a grade II AVCR in the left eye. An MRI of the head and orbits showed no intracranial AV malformations.

CONCLUSIONS

This case agrees with the expected findings for a grade I or II AVCR. Visual acuity is usually unaffected, and associated systemic AV communications are typically not found in a grade I or II AVCR. Grade III AVCR is the most severe form, and is often linked with a life-threatening midbrain AV malformation.

Ocular retardation mouse caused by Chx10 homeobox null allele: impaired retinal progenitor proliferation and bipolar cell differentiation

Ocular retardation (or) is a murine eye mutation causing microphthalmia, a thin hypocellular retina and optic nerve aplasia. Here we show that mice carrying the OrJ allele have a premature stop codon in the homeobox of the Chx10 gene, a gene expressed at high levels in uncommitted retinal progenitor cells and mature bipolar cells. No CHX10 protein was detectable in the retinal neuroepithelium of orJ homozygotes. The loss of CHX10 leads both to reduced proliferation of retinal progenitors and to a specific absence of differentiated bipolar cells. Other major retinal cell types were present and correctly positioned in the mutant retina, although rod outer segments were short and retinal lamination was incomplete. These results indicate that Chx10 is an essential component in the network of genes required for the development of the mammalian eye, with profound effects on retinal progenitor proliferation and bipolar cell specification or differentiation. off

Neural tube defects and abnormal brain development in F52-deficient mice

F52 is a myristoylated, alanine-rich substrate for protein kinase C. We have generated F52-deficient mice by the gene targeting technique. These mutant mice manifest severe neural tube defects that are not associated with other complex malformations, a phenotype reminiscent of common human neural tube defects. The neural tube defects observed include both exencephaly and spina bifida, and the phenotype exhibits partial penetrance with about 60% of homozygous embryos developing neural tube defects. Exencephaly is the prominent type of defect and leads to high prenatal lethality. Neural tube defects are observed in a smaller percentage of heterozygous embryos (about 10%). Abnormal brain development and tail formation occur in homozygous mutants and are likely to be secondary to the neural tube defects. Disruption of F52 in mice therefore identifies a gene whose mutation results in isolated neural tube defects and may provide an animal model for common human neural tube defects.

A behavioral screen for isolating zebrafish mutants with visual system defects

Optokinetic and phototactic behaviors of zebrafish larvae were examined for their usefulness in screening for recessive defects in the visual system. The optokinetic response can be reliably and rapidly detected in 5-day larvae, whereas the phototactic response of larvae is variable and not robust enough to be useful for screening. We therefore measured optokinetic responses of mutagenized larvae as a genetic screen for visual system defects. Third-generation larvae, representing 266 mutagenized genomes, were examined for abnormal optokinetic responses. Eighteen optokinetic-defective mutants were identified and two mutants that did not show obvious morphological defects, no optokinetic response a (noa) and partial optokinetic response a (poa), were studied further. We recorded the electroretinogram (ERG) to determine whether these two mutations affect the retina. The b-wave of noa larvae was grossly abnormal, being delayed in onset and significantly reduced in amplitude. In contrast, the ERG waveform of poa larvae was normal, although the b-wave was reduced in amplitude in bright light. Histologically, the retinas of noa and poa larvae appeared normal. We conclude that noa larvae have a functional defect in the outer retina, whereas the outer retina of poa larvae is likely to be normal.

Ocular abnormalities in neurofibromatosis 2

PURPOSE

To evaluate the ocular abnormalities in patients with clinically diagnosed neurofibromatosis 2 and asymptomatic gene carriers.

METHODS

Probands were ascertained through a surgical otolaryngology practice. In a cross-sectional study, we examined 49 patients with neurofibromatosis 2, 30 offspring of patients, and, as a comparison group, 18 parents and siblings of patients with sporadic neurofibromatosis 2. The examination included a complete neuro-ophthalmic assessment, physical examination, and, for patients and first-degree relatives at risk, cranial and spinal magnetic resonance imaging with gadolinium enhancement, if not previously performed.

RESULTS

The most common ocular abnormalities were posterior subcapsular or capsular, cortical, or mixed lens opacities in 33 (67%) of 49 patients with neurofibromatosis 2 and retinal hamartomas in 11 (22%). We used segregation analysis to determine the mutation carrier status of six at-risk offspring who were 30 years old or younger in two multigeneration families. Three asymptomatic mutation carriers had cataracts, whereas those who were predicted not to carry the mutation did not have cataracts. Asymptomatic mutation carriers may have developmental abnormalities of the eye that are detectable in childhood or adolescence, a finding that may assist in early diagnosis of the disease.

CONCLUSIONS

A variety of ocular abnormalities are present in neurofibromatosis 2, including cataracts, retinal hamartomas, and ocular motor deficits. Many of these are developmental or acquired early in life and may assist in presymptomatic diagnosis. For screening at-risk relatives of patients with neurofibromatosis 2, the types of cataract that are most suggestive of neurofibromatosis 2 are plaque-like posterior subcapsular or capsular cataract and cortical cataract with onset under the age of 30 years.

Mice lacking cyclin D1 are small and show defects in eye and mammary gland development

Using homologous recombination, mice lacking cyclin D1 were generated by replacing most of the first exon of the Cyl-1 gene with sequences encoding neomycin resistance. Cyl-1(-1-) mice were viable and fertile but consistently smaller than their heterozygous or wild-type littermates. The nullizygous animals also showed two distinctive abnormalities: a severe retinopathy caused by impaired development of all layers of the retina and, in the mammary gland during pregnancy, a marked reduction in acinar development accompanied by a failure to lactate. Approximately 50% of animals also had a malformation of the jaw that manifested itself as a misalignment of the incisor teeth. Mouse embryo fibroblasts isolated from 14 day nullizygous, heterozygous, or wild-type embryos and grown under standard conditions showed similar cell-cycle and growth characteristics. Thus although cyclin D1 kinase activity may facilitate G1 progression, it is not essential for the development of most tissues and organs, and only a few specialized cell lineages are demonstrably sensitive to its absence.

Blepharophimosis syndrome: association with colobomatous microphthalmos

OBJECTIVE

To highlight the association of colobomatous microphthalmos with blepharophimosis syndrome.

RESULT

We present a case of blepharophimosis syndrome associated with bilateral optic disc, retinochoroidal and iris colobomas, and microphthalmos, in a Caucasian boy. Inheritance in this case was autosomal dominant from the maternal side.

CONCLUSION

Colobomatous microphthalmos is an infrequent ocular abnormality in the blepharophimosis syndrome. Ophthalmologists should be aware of this association.

Atypical retinochoroidal coloboma in patients with dysplastic optic discs and transsphenoidal encephalocele

OBJECTIVE

To evaluate the clinical significance of V- or tongue-shaped infrapapillary retinochoroidal depigmentation in association with dysplastic optic discs.

METHODS

Clinical data from all patients with V- or tongue-shaped infrapapillary retinochoroidal depigmentation and dysplastic optic discs were evaluated retrospectively.

RESULTS

Five patients with this atypical colobomatous anomaly had transsphenoidal encephalocele. A sixth patient had an ectopic midline pharyngeal mass with no skull-base defect.

CONCLUSION

In patients with optic disc dysplasias, the finding of this V- or tongue-shaped retinochoroidal pigmentary anomaly should prompt neuroimaging to look for transsphenoidal encephalocele.

Defective glia induce neuronal apoptosis in the repo visual system of Drosophila

The role of glia in suppressing neuronal cell death was investigated in the visual system of the Drosophila mutant, reversed polarity (repo). The repo locus encodes a glial-specific homeodomain protein expressed in the optic lobes. Here, we show that survival of the laminar neurons in the optic lobe depends on repo expression in the laminar glia, indicating that the laminar glia supply factors required for neuronal survival. The repo glia also underwent cell death, suggesting that the laminar neurons are required for survival of the glia or that repo expression is required to suppress an intrinsic cell suicide program. Subsequent to the laminar cell death, the retinal cells in the repo visual system also degenerated, indicating that the retinal cell death was due to retrograde degeneration.

MARCKS deficiency in mice leads to abnormal brain development and perinatal death

The MARCKS protein is a widely distributed cellular substrate for protein kinase C. It is a myristoylprotein that binds calmodulin and actin in a manner reversible by protein kinase C-dependent phosphorylation. It is also highly expressed in nervous tissue, particularly during development. To evaluate a possible developmental role for MARCKS, we disrupted its gene in mice by using the techniques of homologous recombination. Pups homozygous for the disrupted allele lacked detectable MARCKS mRNA and protein. All MARCKS-deficient pups died before or within a few hours of birth. Twenty-five percent had exencephaly and 19% had omphalocele (normal frequencies, < 1%), indicating high frequencies of midline defects, particularly in cranial neurulation. Nonexencephalic MARCKS-deficient pups had agenesis of the corpus callosum and other forebrain commissures, as well as failure of fusion of the cerebral hemispheres. All MARCKS-deficient pups also displayed characteristic lamination abnormalities of the cortex and retina. These studies suggest that MARCKS plays a vital role in the normal developmental processes of neurulation, hemisphere fusion, forebrain commissure formation, and formation of cortical and retinal laminations. We conclude that MARCKS is necessary for normal mouse brain development and postnatal survival.

Ophthalmoscopic visualization of the inferior ophthalmic vein through a chorioretinal coloboma

PURPOSE/METHODS

In a patient with a coloboma of the optic nerve, inferior retina and choroid, and deep portions of the sclera, a retrobulbar vessel moved irregularly relative to the retinal vessels, which moved contiguously with the posterior globe.

RESULTS/CONCLUSION

Fluorescein angiography showed the retrobulbar vessel filling slightly later than overlying retinal vessels. We conclude that the retrobulbar vessel was a vein situated inferiorly to the optic nerve.

[The retinal fold in premature infants]

More and more authors point out the existence of the retinal folds at the prematures with retrolental fibroplasia. This form is considered to be achieved. The survey has been done during 3 years on 27 children, divided in 2 groups: the former was the group of the prematures with retinal fold present in retrolental fibroplasia, and the later was the group of children with congenital retinal fold, but born at time. Clinically, the difference between the two types of folds is not so obvious, but from the morphoscopical aspect they differ. The therapy of the diagnosed children was the usual one done in complications: strabismus, cataract, retinal detachment. The conclusions is that, besides the malformative retinal fold of the child born at time, another similar lesion provoked by the prematurity and abusive oxygenation is possible.

Retinal changes associated with neurofibromatosis 2

INTRODUCTION

Neurofibromatosis (NF) is now known to be more than one disease. NF2, formerly classified as central neurofibromatosis, is characterized by bilateral vestibular schwannomas, previously termed "acoustic neuromas", and is much less common than NF1. Lens opacities at an early age have been described in approximately 85% of NF2 patients.

PURPOSE

To determine the frequency of retinal abnormalities in NF2 patients.

METHODS

We prospectively examined 15 consecutive patients who met the diagnostic criteria of NF2.

RESULTS

We observed an epiretinal membrane in the macular or paramacular area in 12 of 15 patients, and a combined pigment epithelial and retinal hamartoma in the macula of one patient who also had an epiretinal membrane in the macula of the other eye. Additionally, 11 patients had central posterior cortical, subcapsular, or peripheral cortical lens opacities.

CONCLUSIONS

Children or young patients with epiretinal membranes, combined pigment epithelial retinal hamartoma, and lens opacities that are not the result of other ocular disorders should have a neurologic evaluation and a careful family history for NF2.

The effects of PSK, a biological response modifier, on congenital ocular abnormalities induced by X-ray irradiation

The antiteratogenic effects of PSK, a biological response modifier, were examined using histological and developmental analysis. The whole bodies of pregnant mice were irradiated with X-rays and injected with PSK within ten minutes after irradiation on day 7 of gestation (E7). The foetuses on E18 were examined and a high incidence of malformations were observed in X-ray irradiated embryos. Microphthalmia was the most frequent malformation. PSK administration suppressed the X-ray irradiation-induced ocular anomalies in not only the frequency, as deduced by external observation, but also in histopathological changes in the retina, lens, and cornea. In particular, the incidence of lens aplasia was significantly decreased by PSK administration. Developmental analysis using E10 and E13 embryos revealed that the decrease in the incidence of histopathological changes was first observed within 72 hours after PSK administration. In addition, X-ray irradiation-induced early foetal death (E10-13) was also suppressed by PSK administration. The possible mechanisms of the antiteratogenic effects of PSK are discussed.

Abnormal electroretinogram associated with developmental brain anomalies

PURPOSE

We have encountered abnormal ERGs associated with optic nerve hypoplasia, macular, optic nerve and chorioretinal colobomata and developmental brain anomalies. Brain anomalies include cortical dysgenesis, lissencephaly, porencephaly, cerebellar and corpus callosum hypoplasia. We describe six exemplar cases.

METHODS

Scotopic and photopic ERGs adherent to international standards were performed as well as photopic ERGs to long-duration stimuli. CT or MRI studies were also done. The ERGs were compared to age-matched normal control subjects.

RESULTS

ERG changes include reduced amplitude b-waves to blue and red stimuli under scotopic testing conditions. Implicit times were often delayed. The photopic responses also showed reduced amplitude a- and b-waves with implicit time delays. The long-duration photopic ERG done in one case shows attenuation of both ON- and OFF-responses.

CONCLUSIONS

Common underlying developmental genetic or environmental unifying casualties are speculated to be at fault in causing these cases of associated retinal and brain abnormalities. No single etiology is expected. Multiple potential causes acting early in embryogenesis effecting neuronal induction, migration and differentiation are theorized. These occur at a time when brain and retinal cells are sufficiently undifferentiated to be similarly effected. We call these cases examples of Brain Retina Neuroembryodysgenesis (BRNED). Homeobox and PAX genes with global neuronal developmental influences are gene candidates to unify the observed disruption of brain and retinal cell development. The ERG can provide a valuable clinical addition in understanding and ultimately classifying these disorders.

Ocular findings associated with a Cys39Arg mutation in the Norrie disease gene

OBJECTIVE

To diagnose the carriers and noncarriers in a family affected with Norrie disease based on molecular analysis.

DESIGN

Family members from three generations, including one affected patient, two obligate carriers, one carrier identified with linkage analysis, one noncarrier identified with linkage analysis, and one female family member with indeterminate carrier status, were examined clinically and electrophysiologically. Linkage analysis had previously failed to determine the carrier status of one female family member in the third generation. Blood samples were screened for mutations in the Norrie disease gene with single-strand conformation polymorphism analysis. The mutation was characterized by dideoxy-termination sequencing.

RESULTS

Ophthalmoscopy and electroretinographic examination failed to detect the carrier state. The affected individuals and carriers in this family were found to have a transition from thymidine to cytosine in the first nucleotide of codon 39 of the Norrie disease gene, causing a cysteine-to-arginine mutation. Single-strand conformation polymorphism analysis identified a patient of indeterminate status (by linkage) to be a noncarrier of Norrie disease.

CONCLUSION

Ophthalmoscopy and electroretinography could not identify carriers of this Norrie disease mutation. Single-strand conformation polymorphism analysis was more sensitive and specific than linkage analysis in identifying carriers in this family.

Kidney and retinal defects (Krd), a transgene-induced mutation with a deletion of mouse chromosome 19 that includes the Pax2 locus

The semidominant mutation Krd (kidney and retinal defects) was identified in transgenic line Tg8052. Krd/+ mice have a high incidence of kidney defects including aplastic, hypoplastic, and cystic kidneys. Retinal defects in Krd/+ mice include abnormal electroretinograms and a reduction of cell numbers that is most extreme in the inner cell and ganglion layers. Viability of Krd/+ mice is strongly influenced by genetic background, and growth retardation is observed in young animals. Homozygosity results in early embryonic lethality. Fluorescence in situ hybridization of a transgene-specific probe localized the insertion site to the distal region of mouse Chromosome 19. The sequence of the insertion site revealed transgene insertion into a LINE element with deletion of a single nucleotide from the 3' terminus of the transgene. A polymorphic microsatellite, D19Umi1, was identified in a junction clone and mapped in several large crosses. D19Umi1 is located 1.7 +/- 1.0 cM distal to Pax2, which encodes a paired type transcription factor expressed in embryonic kidney and eye. Deletion of Pax2 from the transgenic chromosome was demonstrated by Southern analysis of genomic DNA from (Krd/+ x SPRET/Ei)F1 mice. Additional genetic and molecular data are consistent with an approximately 7-cM deletion that includes the loci stearoyl CoA desaturase (Scd1), pale ear (ep), D19Mit17, D19Mit24, D19Mit27, D19Mit11, and Pax2. This deletion, Del(19)TgN8052Mm, will be useful for genetic and functional studies of this region of mouse Chromosome 19.

The molecular biology of Norrie's disease

The Norrie's disease gene has been accurately located on the short arm of the X chromosome. The methodology underlying this achievement and the structure of the three-exon gene is described in this review article. The clinical implications of these recent advances are discussed. Allelic variants of Norrie's disease and the phenomenon of females affected by X-linked disease are also discussed.

Oral-facial-digital syndrome with retinal abnormalities: OFDS type IX. A further case report

The oral-facial-digital syndromes (OFDS) are a heterogeneous group. Recently, Gurrieri et al. [1992: Am J Med Genet 42:789-792] described a new OFDS characterised by typical oral, facial and digital abnormalities but distinguishable from previously reported OFDS by the presence of retinochoroidal lacunae of an apparently colobomatous origin. Toriello [1993: Clin Dysmorph 2:95-105] designated this possible new OFDS as Type IX. We describe a young woman presenting with oral, facial and digital anomalies and with the specific retinal abnormality reported by Gurrieri et al. [1992], thus confirming the existence of OFDS Type IX. As the patients of Gurrieri et al. [1992] were two affected brothers, they were unable to distinguish between autosomal and X-linked recessive inheritance. As our patient is an affected female, an autosomal recessive mode of inheritance is more likely.

Aetiology of severe visual impairment and blindness in microphthalmos

Microphthalmos occupies a spectrum from a normal, but small globe, to a globe with multiple anterior and posterior segment abnormalities. This study examines 54 eyes of 27 patients who had bilateral microphthalmos and severe visual impairment or blindness. Congenital cataract was the commonest cause of severe visual impairment (44%), followed by presumed retinal or optic nerve dysplasia (30%) and chorioretinal coloboma (22%). Lensectomy was followed by phthisis bulbi in 3/23 cases and retinal detachment in 2/23 cases. There were no cases of angle closure glaucoma. The three clinical conditions associated with a poor prognosis were cataract, chorioretinal coloboma, and a markedly reduced corneal diameter. A corneal diameter of 6 mm or less was associated with a visual acuity of no perception of light in 81% (21/26) compared with 4% (1/28) of those with larger corneas.

The association of cleft lip and palate with Aicardi syndrome

In summary, Aicardi syndrome is defined by its tetrad of infantile spasms, agenesis of the corpus callosum, mental retardation, and chorioretinal lacunae. We report a case of Aicardi syndrome with associated cleft lip and palate. This is an infrequent finding that is present in approximately 3 percent of reported cases. Plastic surgeons should be aware of this association when treating patients with cleft lip and palate.