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Leber congenital amaurosis (LCA) is a retinitis pigmentosa with early onset, leading to blindness in infants. There is currently no efficient therapy to treat LCA. At the present time, mutations in seven different genes have been associated with the disease (Hanein et al. 2004). In 10 to 15% of the cases LCA originates from a mutation in RPE65 (Gu et al. 1997), a gene specifically expressed in the cells of the retinal pigment epithelium layer (RPE cells). This gene encodes a 65kD protein the function of which has been dissected in a recently published study demonstrating its crucial role as a regulator of the visual cycle and a chaperone for the chromophore of the visual pigment (Xue et al. 2004). The patients affected by a mutation in this gene could benefit from a substitutive gene therapy consisting in the transfer of a fully functional allele of the RPE65 gene in RPE cells. Furthermore, animal models of RPE65 mutations have been identified (Aguirre et al. 1998; Veske et al. 1999) or genetically produced (Redmond et al. 1998) and thus provide the necessary tools to set up the conditions of such a strategy before a clinical trial can be started. The proof of feasibility of this approach has indeed already been established in dogs bearing a spontaneous mutation in the RPE65 gene (Acland et al. 2001; NarfstrÖm et al. 2003), as well as in knock-out mice (Dejneka et al. 2004; Lai et al. 2004). These studies have shown that an adeno-associated virus (AAV)-derived vector is able to deliver the RPE65 gene to RPE cells and thus to restore vision at least partially. Nevertheless, before a clinical trial can take place, a great effort must be provided to assess the bio-safety of the procedure. In particular, trans-gene expression has to be tightly controlled to achieve the following criteria: (i) expression should occur only in RPE cells; (ii) expression should reach the therapeutic level without disturbing the homeostasis of the target cells. [ABSTRACT FROM AUTHOR]

The delivery of foreign DNA to the retina has proven to be a valuable tool for investigations of retinal disease, development, and complex cellular interactions. To achieve efficient and stable retinal gene expression with minimal unwanted side effects, viral vectors derived from AAV (adeno-associated virus) and LV (lentivirus) remain the vehicles of choice. LV vectors have gained recent attention in CNS gene delivery due in part to their large transgene capacity, however contradictory results regarding retinal transduction ability exist in the literature. We sought specifically to characterize the temporal and spatial expression pattern of LV vectors when delivered to the rodent retina. [ABSTRACT FROM AUTHOR]

In eukaryotic cells, gene expression is controlled at multiple levels that could be grouped in two large categories, transcriptional and post-transcriptional regulatory events. Regulation of gene expression at the level of transcription is the major determinant of the initiation of protein synthesis and of the level of gene expression. However, there is increasing evidence of the important contribution of the post-transcriptional control mechanisms in determining and fine-tuning the final amount of the synthesized protein product. Post-transcriptional regulatory mechanisms could be grouped into events that modulate mRNA stability, localization, translation, as well as protein stability and modifications. [ABSTRACT FROM AUTHOR]

RNA interference (RNAi) is an evolutionarily ancient method of genome defense in many organisms. RNAi is triggered when a cell encounters a long double-stranded RNA (dsRNA) and results in the silencing of gene expression (Fire et al., 1998). The dsRNA is processed by the RNAse III-like nuclease, Dicer, into 20-25nt duplex RNA, termed short interfering RNA (siRNA, Zamore et al., 2000; Hammond et al., 2000). The siRNAs assemble into RNA-induced silencing complexes (RISCs) containing endoribonucleases and are unwound. It is believed that the sense strands are degraded, while the anti-sense strands activate the RISC to participate in repeated cycles of cleavage and degradation of complementary cognate mRNA, effectively silencing the gene such that no protein is made. For this reason, RNAi is seen as a useful tool for analyzing gene function. Given that introducing long dsRNA into mammalian cells initiates a potent antiviral response (Stark et al., 1998), most investigators bypass this by introducing or expressing siRNAs, which are the key mediators of RNAi (Elbashir et al., 2001a and b). [ABSTRACT FROM AUTHOR]

Retinal neovascularization is a feature shared by many disease processes including diabetic retinopathy, retinopathy of prematurity, branch retinal vein occlusion and central retinal vein occlusion, which are collectively referred to as ischemic retinopathy (Campochiaro, 2000). Retinal neovascularization is the most common cause of blindness in young diabetic patients. Investigations of the pathogenic mechanisms and therapeutic interventions for retinal neovascularization require reproducible and clinically related animal models. Currently, all diabetic models exhibit only early retinal vasculopathy after 1 or 2 years of the disease (Kondo and Kahn, 2004). The lack of retinal neovascularization in diabetic models is probably due to the natural short life span of rodents (2-3 years). In humans, DR is detected only after at least 3 years of diabetes (Dorchy et al., 2002). As angiogenesis is tightly controlled by the relative balance of stimulators and inhibitors, a shift in their balance, such as increased expression of vascular endothelial growth factor (VEGF) or decreased production of pigment epithelium-derived factor, would initiate angiogenesis (Okamoto et al., 1997; Ruberte et al., 2004; Renno et al., 2002). It is clear from literature that ischemia-induced upregulation of VEGF is a potent mediator of retinal neovascularization (Campochiaro, 2000; Miller, 1997). Animal models of retinal neovascularization have been established by oxygen-induced retinal ischemia, photodynamically-induced retinal branch vein occlusion and intravitreal implantation of VEGF sustained-release pellets (Campochiaro, 2000; Saito et al., 1997; Ozaki et al., 1997; Tolentino et al., 2002). However, retinal neovascularization in these animal models is either transient or occurs with a delayed onset. [ABSTRACT FROM AUTHOR]

During the past two decades, zebrafish (Danio rerio) have become established as a prolific model for biological research (for review, see Udvadia and Linney, 2003). Zebrafish exhibit many features of an ideal model organism, including small size, rapid development, and high fecundity. Since zebrafish are vertebrates, there is a conservation of physiology with higher vertebrates, including humans. Juvenile zebrafish develop rapidly and oviparously, facilitating developmental studies without invasive procedures. Zebrafish are amenable to drug discovery, having similar responses to mammals in pharmacological tests using cardiovascular, anti-angiogenic and anti-cancer drugs (for review, see Langheinrich et al., 2002). To date, zebrafish have been used in genetic screens to identify genes involved in development and function of organs including the eye, brain, ear and heart (Haffter et al., 1996). More recently, transgenic technologies have been developed for zebrafish. In this review, we will describe how this transgenic technology can be applied to study retinal biology. [ABSTRACT FROM AUTHOR]

Diabetic retinopathy is a severe complication of diabetes leading to some degree of vision impairment in long-term diabetes sufferers. Currently, the most successful treatment available for diabetic retinopathy is laser photocoagulation, a therapy that destroys part of the retina to save central vision. The principal aim of laser photocoagulation in the treatment of diabetic retinopathy is to effect regression of abnormal vessels, reduce oxygen tension and reverse angiogenesis in the retina. Although laser photocoagulation has been employed for more than 30 years, its underlying molecular mechanisms remain unknown. Research is now focused on identifying and understanding these factors, to ultimately develop therapies to protect against the initiation and progression of neovascularisation. [ABSTRACT FROM AUTHOR]

Tight junctions (TJ) are specialized multiprotein complexes which act to seal the intercellular space and thereby generate a permeability barrier required for transport processes (Matter and Balda, 1999). In addition, by regulation of the TJs, the paracellular pathway may be opened for selective transport of molecules, ions (Madara et al., 1992) and neutrophils (Huber et al., 2000). Thus far several interacting constituents comprising of transmembrane proteins including occludins (OCLN-TM4+/TM4− and 1B), claudins with >20 members and a series of cytoplasmic plaque proteins including ZO-1, -2, or -3, cingulin, 7H6 and symplekin have been identified in several tissue types of different species (Citi and Cordenonsi, 1998; Furuse et al., 1993; Ghassemifar et al., 2002; Matter and Balda, 1999; Mitic and Anderson, 1998). While the inner blood-retinal barrier, the retinal vascular endothelial cells, maintain a restricted and regulated trans-/paracellular transport from the blood to the surrounding tissue, the outer blood-retinal barrier, the retinal pigment epithelium (RPE), provides a permeability barrier between the retina and the choroid allowing vectorial exchange of solutes between these layers (Thumann, 2001). The RPE plays an important role in the proper function and maintenance of the photoreceptors by releasing differentiation and survival promoting factors. Despite the identification of TJ proteins in retinal tissue, little is known about the effect of pathological insult, such as hypoxia, on the expression of TJ proteins (Mark and Davis, 2002). It has also been reported that factors present in embryonic or whole eye-extract can influence the neurons of chick sympathetic ganglia to express choline acetyltransferase (Iacovitti et al., 1987) and also support full survival ganglion neurons for up to 6 days in culture (Margiotta and Howard, 1994). Retinal hypoxia has been reported to increase production of vascular endothelial growth factor (VEGF), a known stimulant of retinal neovascularization (Okamoto et al., 1997). The aim of this study was to investigate the regulation of tight junction (TJ) gene expression in cultured retinal pigment epithelial (RPE) cells and in the retina of normal and vascular endothelial growth factor (VEGF) transgenic mice. [ABSTRACT FROM AUTHOR]

The retina is an important model for studies of neurodegeneration. More than 100 gene mutations are known to cause retinal degeneration (Chader, 2002; Pacione et al., 2003; Rattner et al., 1999). Studies of retinal degeneration in mammals have focused on mouse because of the knowledge of its genome together with the ease of its breeding and husbandry (Naash et al., 2004; Olsson et al., 1992; Pinto et al., 2004). Assessment of the progression of retinal degeneration generally involves measurements of retinal sensitivity using the electroretinogram (ERG) and analysis of retinal anatomy using histological and histochemical techniques. In addition to knowledge of the anatomical and physiological consequences of retinal degeneration, it is important to assess its affect on visual function, that is, to answer the critical question: "How well can a mouse see?" [ABSTRACT FROM AUTHOR]

The generation of gene knockout mice by injection of homologous gene targeted embryonic stem (ES) cells into blastocyst has rapidly advanced our knowledge of gene function in mammals. However, knockout of essential genes often causes embryonic or neonatal lethality and thus obscures the particular role of genes in a target tissue or in adults. To circumvent this problem and disrupt genes in a temporal and spatial fashion, the Cre/lox system based gene targeting strategy has become a method of choice (for review, see Le and Sauer (2000)). This method can also be used in dissection of the roles of multifunctional genes in a particular tissue/cell-type. To study the function of widely expressed essential genes in the retinas, we are systematically establishing Cre/lox conditional knockout systems in retinal cells. This report is a review of our recent work on the generation and characterization of the cone-specific cre mice (Le et al., 2004). [ABSTRACT FROM AUTHOR]

Retinal neovascularisation is a major clinical complication of diabetic retinopathy that takes place late in the disease process and constitutes the most damaging phase resulting in loss of vision (Klein et al., 1984). Neovascularisation is defined as the growth of new blood vessels which, in a disease process such as diabetic retinopathy, occurs in abnormal retinal locations. Long term consequences of retinal neovascularisation include the formation of epiretinal membranes and retinal detachment (Smith et al., 1999). In addition, new blood vessels lack a patent blood retinal barrier and exhibit leukostasis presumably resulting in cytotoxic damage (Ishida et al., 2003; Qaum et al., 2001). [ABSTRACT FROM AUTHOR]

Leukemia inhibitory factor (LIF) is a member of the interleukin 6 (IL-6) family of cytokines, which also includes oncostatin-M, ciliary neurotrophic factor (CNTF), interleukin-11, and cardiotrophin-1. Members of this family are grouped together based on activation of a common tyrosine kinase receptor, gp130. (Ip et al, 1992) The expression of activating ligands of gp130, including LIF and CNTF, have been localized to Muller glial cells and microglial cells in the retina. (Harada et al, 2002; Kirsch et al, 1997; Neophytou et al, 1997; Walsh et al, 2001) While little is known about the regulated expression of LIF in the eye, CNTF has been shown to be up-regulated in the retina following injury or stress. (Cao et al, 1997; Wen et al, 1995; Wen et al, 1998) This up regulation has led to the hypothesis that activation of gp130 is an endogenous mechanism for neuroprotection in the retina. In support of this hypothesis, it has been shown that activating gp130 either by direct injections of LIF or CNTF into the eye or by their expression from transduced cells is effective at protecting retinal neurons from cell death. This includes cell death caused by prolonged exposure to constant light and inherited retinal degenerative mutations (Bok et al, 2002; Cayouette and Gravel, 1997; LaVail et al, 1998; LaVail et al, 1992). CNTF and LIF are both currently in clinical trials for the treatment of neurological degenerative disorders including amyotrophic lateral sclerosis (Festoff, 1996) and retinitis pigmentosa (www.clinicaltrials.gov). While CNTF and LIF are effective at preventing cell death, the mechanism has not yet been identified. [ABSTRACT FROM AUTHOR]

The basic helix loop helix (bHLH) transcription factors collectively mediate cellular differentiation in almost every type of tissue including the retina (Murre et al. 1989; Jan and Jan 1993; Cepko 1999). Class A factors are ubiquitously expressed throughout mammalian tissue, while the expression of class B factors are cell type specific. These factors have both a DNA binding domain and helix loop helix domain (HLH) protein dimerization domain. Class B factors usually heterodimerize with the ubiquitously expressed, bHLH factors, such as E12/E47. Because of their importance during photoreceptor development, bHLH factors are candidate genes for photoreceptor degeneration. We have examined the roles of two bHLH factors, both which are expressed during retinal development, but also share the property of continued expression in the adult retina. [ABSTRACT FROM AUTHOR]

The photoreceptor disk membrane protein peripherin/rds is essential for the outer segment morphogenesis and integrity. Peripherin/rds associates with itself and with its homologue Rom-1 to form homo- and hetero-complexes, which are necessary for its structural role (Goldberg et al., 1995; Molday, 1998). More than seventy different pathogenic mutations in the peripherin/rds gene have been identified. These mutations are divided primarily into two categories: those associated with classic retinitis pigmentosa (RP), and those associated with various forms of macular dystrophy (MD). In fact, mutations in peripherin/rds account for 5-10% of RP causes, and is a major cause for MD (Kohl et al., 1998; Molday, 1998; http://www.sph.uth.tmc.edu/RetNet; http://www.retina-international.org/scinews/rdsmut.htm). Insights into the functional significance, structural role, and pathogenic effects of this protein have been accumulating considerably since its initial description; this is largely accomplished by the use of laboratory animal models. Use of transgenic or knock-out animals holds great potential for the investigation of retinal disease pathogenesis and the exploration of therapeutic interventions. Table 21.1 summarizes the animal models used to investigate the disease-causing mutations in peripherin/rds. In addition to the pathogenesis study, transgenic mouse and Xenopus laevis expressing the wild type peripherin/rds or the C-terminus have also been used to explore the structural and functional significance of the protein (Loewen et al., 2003; Ritter et al., 2004). [ABSTRACT FROM AUTHOR]

Genomic analysis, from patients with retinal diseases such as retinitis pigmentosa (RP) and congenital night blindness (CNB), has provided convincing evidence that various subtypes of retinal diseases can result from mutations in the gene encoding rod opsin, a protein that binds 11-cis retinal to form the visual pigment, rhodopsin. Over 100 different mutations in this gene have been documented, and shown to co-segregate with autosomal dominant RP (Berson et al., 2002; Farrar et al., 2002; Nour and Naash, 2003) as well as a few other mutations with CNB (Dryja et al., 1993; Sieving et al., 1995; al Jandal et al., 1999). Interestingly when these CNB causing mutations are expressed in COS cells, they constitutively activated transducin in the dark while in the absence of 11-cis retinal (Dryja et al., 1993; Rao et al., 1994; Gross et al., 2003a; Gross et al., 2003b). Thus, the in vitro data suggests that the CNB mutations generate a persistent ‘dark light' that saturates the rod photocurrent and severely depresses rod sensitivity in a manner similar to that produced by light. One of these CNB mutations resulted from the replacement of glycine at position 90 by aspartic acid (G90D), which has been shown to associate with an unusual trait of congenital stationary night blindness (CSNB) (Sieving et al., 1995). [ABSTRACT FROM AUTHOR]

The vertebrate retina is a specialized neural network that contains very sensitive signal transducers—the rod and cone photoreceptors. Rods function in near darkness (scotopic) and are responsible for dim light vision, while cones operate in bright light (photopic) and provide daytime, high acuity color vision. In the human retina, rods are the dominant photoreceptor cell type and comprise about 95% of all photoreceptor cells, while cones account for only 5% of the cells. Yet in a bright light environment, normal cone function is essential for visual perception since rods become saturated and are rendered nonfunctional. [ABSTRACT FROM AUTHOR]

In the retina photoreceptor and retinal pigment epithelial cells (RPE cells) are in close contact. The outer segment portions of photoreceptors consist of stacked membranous disks containing the phototransduction machinery. These disks are permanently produced thereby lengthening outer segments. To maintain constant outer segment length photoreceptors eliminate their most aged tips by daily shedding (Young, 1967). [ABSTRACT FROM AUTHOR]

RPE65 is a major protein in the retinal pigment epithelium (RPE) (Hamel et al., 1993), where it is required for the regeneration of 11-cis retinal, the native ligand of rod and cone opsins, in the dark (Redmond et al., 1998). Therefore, the retina of the Rpe65-/- mouse is almost completely depleted of 11-cis retinal, resulting in a minimal level of photosensitivity. This observation poses several questions, of which we will only address three: first, which cell type (rods and/or cones) is responsible for the remaining photosensitivity; second, if only one cell type remains photosensitive, what happens to the other one; and third, what is the chromophore that enables the formation of light-sensitive pigment? Early reports have disagreed whether the remaining photosensitivity can be attributed to rod (Seeliger et al., 2001) or cone function (Redmond et al., 1998; Ekesten et al., 2001). Double knockout experiments, crossing the Rpe65-/- with either the rhodopsin or the cone cGMP-gated channel knockout, respectively, revealed that the remaining photosensitivity in the young adult and old Rpe65-/- mouse retina (>6 weeks-of-age) can be attributed to rod sensitivity (Seeliger et al., 2001). This leaves open the question as to the possible fate of the cone photoreceptors in the absence of RPE65. Likewise, early reports demonstrated a slow degeneration in particular of the rod photoreceptors (Redmond et al., 1998), suggesting that the accumulation of the retinyl ester in the RPE might contribute to the demise of the photoreceptors. However, in the Rpe65-/-::Gnat1-/- mouse, in which similar elevated amounts of retinyl ester have been reported to accumulate in the RPE, no rod degeneration occurs (Woodruff et al., 2003). And finally, with respect to the available chromophore; several groups have tried to obtain a spectrum of the pigment from pooled tissue and have failed to do so (Ablonzcy et al., 2001; C. H. Remé, personal communication). Thus, here we would like to further address these three key issues and how our laboratories have investigated them over the past 5 years. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) is a late-onset, neurodegenerative disease of the retina and is the leading cause of catastrophic vision loss in the elderly. AMD usually occurs in people over the age of 65 years (Javitt et al., 2003) and accounts for approximately 50% of registered blindness in Western Europe and North America (Mitchell et al., 1998; Vingerling et al., 1995a). It develops as either dry AMD, geographic atrophy, or wet AMD (exudative) (Bird et al., 1995; Green, 1999). Dry AMD is characterized by the presence of sub-retinal pigment epithelium (RPE) deposits including drusen, basal linear deposits and basal laminar deposits (Curcio and Millican, 1999; Sarks, 1976). Geographic atrophy is characterized by RPE atrophy and wet or exudative AMD is characterized by choroidal neovascularization (CNV) (1991) and more recently, retinal angiomatous proliferation (Yannuzzi et al., 2001). In AMD with CNV, tufts of newly formed, functionally incompetent, blood vessels proliferate from the choroid, break through a thickened and fragile Bruch's membrane (Grossniklaus and Green, 2004), and extend laterally into the sub-RPE (Sarks et al., 1980; Tobe et al., 1998a). These vessels in turn, may erode through the RPE, infiltrate the neural sensory retina, and communicate with the retinal circulation in what has been referred to as a retinal-choroidal anastomosis. This is common in the end stage of disciform disease (Yannuzzi et al., 2001). [ABSTRACT FROM AUTHOR]

Retinal pigment epithelium (RPE) is essential for the function and survival of photoreceptor cells by playing supporting roles including shedding the outer segments of the photoreceptor cells, removing metabolic wastes, transporting nutrients and maintaining visual cycle. RPE defects have been found in various human retinal disorders, such as age-related macular degeneration (Zarbin, 1998), Best disease (Petrukhin et al., 1998; Marmorstein et al., 2000), Sorsby fundus dystrophy (Weber et al., 1994; Ruiz et al., 1996; Della et al., 1996), and childhood-onset severe retinal dystrophy (Gu et al., 1997). Animal models with RPE defects have been used to study the molecular basis for the function of the RPE cells. The Royal College of Surgeons (RCS) rat, a model for recessive inherited retinal degeneration, is characterized by the dysfunction of RPE due to a null mutation of the receptor tyrosine kinase Mertk gene (D'Cruz et al., 2000). RPE cells fail to shed the outer segments of the photoreceptor cells in the RCS rat (Mullen et al., 1996). Recently, mice with a targeted disruption of the Mertk gene manifest retinal dystrophy similar to RCS rats (Duncan et al., 2003). In addition, mutated Mertk gene has been identified in patients with retinitis pigmentosa (Gal et al., 2002). [ABSTRACT FROM AUTHOR]

Mutations within the gene encoding inosine monophosphate dehydrogenase 1 (IMPDH1), the rate-limiting enzyme of the de novo pathway of guanine nucleotide biosynthesis, have been shown to cause the RP10 form of autosomal dominant retinitis pigmentosa (RP). This form of RP is generally early-onset and severe in those patients that have been identified to date. The two mutations originally identified in large RP10 families in 2002 were Arg224Pro and Asp226Asn substitutions, and since then several additional mutations have been identified in RP families and individual patients (Kennan et al., 2002; Bowne et al., 2002; Daiger et al., 2003; Grover et al., 2004). [ABSTRACT FROM AUTHOR]

Leber congenital amaurosis (LCA) is a clinically and genetically heterogeneous form of early-onset retinal dystrophy that is usually recessively inherited. LCA is the most rapid and severe form of congenital blindness, and it represents approximately 5% of all inherited retinopathies.1 Clinically, LCA is characterized by severely impaired vision and a weak or absent electroretinogram evident within the first year of life. To date, seven genes have been independently linked to LCA.2 The majority of mutations implicated in the causation of LCA are genetically consistent with recessively inherited loss-of-function pathogenesis mechanisms.2 [ABSTRACT FROM AUTHOR]

Annexins (also known as lipocortins) are a family of calcium and phospholipid-binding proteins. At least 20 members of this family are known, and they have a wide range of potential functions, such as vesicular transport and trafficking, endocytosis, exocytosis and cellcell adhesion. Annexins have molecular weights ranging between 30 and 40kDA (the exception is annexin VI which is 66kDA) and possess striking structural features. To qualify as an annexin, a protein must have 1) the presence of a conserved 70 amino acid domain repeated either 4 or 8 times in the overall structure (annexin VI has an 8 repeating amino acid domain; whereas the rest have 4), 2) the ability to bind phosopholipids in the presence of calcium. Annexins are exported from the cytosol to the exterior of cells across the plasma membrane by an unknown mehanism. When located extracellular, some annexins have been shown to function as receptors for other extracellular proteins: annexin II binds to tenascin and tissue plasminogen activator, while annexin V binds to collagen (Kojima, 1997). [ABSTRACT FROM AUTHOR]

Studies of Stargardt disease suggest a role for RPE lipofuscin in the RPE cell atrophy that characterizes macular degeneration. The best known constituent of RPE lipofuscin is the pyridinium bisretinoid, A2E (Eldred and Lasky, 1993; Parish et al., 1998). Amongst the properties of A2E that may be damaging to the RPE cell is its ability to destabilize cell membranes (Sparrow et al., 1999). A hydrophilic head group combined with a pair of hydrophobic side-arms are the structural correlates of this behavior. This amphiphilic structure accounts for the tendency of A2E to aggregate (Sakai et al., 1996; De and Sakmar, 2002), a behavior first recognized in deuterated chloroform (CDCl3), the broadening of the 1H NMR signal indicating that the protonated pyridinium moieties of A2E were closely packed within the interior of micelles while the hydrophobic chains contacted the solvent. Further evidence of the detergent-like behaviour of A2E has been revealed in experiments demonstrating the ability of A2E to induce concentration-dependent membrane leakage (Sparrow et al., 1999). In studies employing unilamellar vesicles, it has also been shown that A2E, at critical micellar concentrations, can solubilize membranes (De and Sakmar, 2002). [ABSTRACT FROM AUTHOR]

For many years, blue light damage associated with retinal pigment epithelial (RPE) cell lipofuscin (LF) has been implicated in the cause of age-related macular degeneration (AMD) (Young, 1988; Winkler et al., 1999; Bressler et al., 2000) and other retinal degenerative diseases, such as Stargardt's disease, (Lopez et al., 1990; Birnbach et al., 1994), Best's macular dystrophy (Weingeist et al., 1982) and cone-rod dystrophy (Rabb et al., 1986). A2E and isomers, pyridinium bis-retinoid compounds and only major blue-light absorbing fluorophores isolated from human LF, (Eldred and Katz, 1988; Eldred and Lasky, 1993; Sakai et al., 1996; Parish et al., 1998;) account for a small fraction of the composition of LF. Proteins account for 30-70% (Schutt et al., 2002; Haralampus-Grynaviski et al., 2003). The percentage of A2E oxidation products, retinol and retinyl palmitate has not been quantified, yet these compounds, too, make up only a fraction of the composition of LF. Evidence for A2E and especially A2E photo-oxidation products' involvement in AMD is strong (Sparrow et al., 1999; Sparrow et al., 2000; Sparrow and Cai, 2001; Ben-Shabat et al., 2002a; Finnemann et al., 2002; Sparrow et al., 2002; Sparrow et al., 2003); however, their involvement does not rule out the possibility of AMD's etiology being multifactorial. There are many compounds in LF that have not been characterized, some of which may also play a role in the pathogenesis of AMD and other retinal degenerative diseases. [ABSTRACT FROM AUTHOR]

Choroideremia is an X-linked recessive disorder characterized by progressive degeneration of the choroid, RPE and retina Goedblood et al., 1942). Patients initially present with night blindness in the first or second decade that progresses to severe constriction of the visual field. Central acuity is lost late in life (Kril et al.). [ABSTRACT FROM AUTHOR]

Adult-onset foveomacular dystrophy (AOFMD) was first described as a peculiar foveomacular dystrophy in 1974 (Gass, 1974). A mutation in the RDS/peripherin gene (Pro-210- Arg) was identified in this particular kindred (Gorin et al., 1994). Subsequently, Feist and coworkers reported a case of choroidal neovascularization associated with AOFMD in a patient with the Pro-210-Arg mutation (Feist et al., 1994). To our knowledge, CNV in AOFMD is rare as demonstrated by only two other descriptions of it in the literature: 1) Vine and Schatz described three instances in two patients, neither of whom had an identi- fied mutation (Vine et al., 1980); and 2) Battaglia Parodi and coworkers described a case of subfoveal CNV in a vascularized pigment epithelial detachment in a patient with AOFMD (Battaglia et al., 2000). Recently, an A to G change, predicting a Tyr-141-Cys substitution in the RDS/peripherin gene has been described that results in AOFMD which is dominantly transmitted (Yang et al., 2004). In addition, a frameshift mutation in exon 1 of the RDS/peripherin gene, that results in a guanine deletion at nucleotide position 112, leads to a premature termination of the gene product at amino acid 38 and has been implicated in the genesis of AOFMD in a 13-family member kindred (Yang et al., 2003). We present three cases of subfoveal CNV in patients with AOFMD, which were caused by RDS/peripherin gene mutations. [ABSTRACT FROM AUTHOR]

Bietti crystalline corneoretinal dystrophy (BCD) is an autosomal recessive chorioretinal dystrophy characterized by progressive night blindness, tiny, yellowish, glistening retinal crystals, choroidal sclerosis, and crystalline deposits in the peripheral cornea. Recent studies have demonstrated that the CYP4V2 gene which encodes a CYP450 family protein is the causative gene of the disease. We have identified a homozygous mutation in the CYP4V2 gene in 8 separate Japanese patients with BCD and conclude that mutations in the CYP4V2 gene are the major cause of BCD. The IVS6-8_c.810del/insGC mutation is found at a higher frequency in the Asian populations suggesting a founder effect. [ABSTRACT FROM AUTHOR]

Age-related macular degeneration (AMD) is the commonest cause of severe vision loss in adults, affecting up to 30% of the elderly population and accounting for 50-60% of new blind registration in western countries (Green and Enger, 1993; Seddon, 2001). It is characterised by a late-onset degeneration of the retinal macula and represents the advanced stage of a more common disorder, age-related maculopathy. There are two clinical subtypes of AMD, one is a "dry" form characterised by geographic atrophy, the other a "wet" form characterised by choroidal neovascularisation (CNV). This "wet" form represents only 10% of cases but accounts for about 90% of registered blindness (Ferris et al., 1984). The important early pathological features of AMD are the presence of both focal (drusen) and diffuse extracellular (basal) deposits in the macula, between the retinal pigment epithelium (RPE) and inner collagenous layer of Bruch's membrane, a pentalaminar structure bounded by the basement membranes of RPE and choroidal capillary 1endothelium. These deposits lead to dysfunction and later death of RPE and associated photoreceptors. The nature of the proteins within the diffuse extracellular deposits have not been elucidated but the focal deposits (drusen) include >100 proteins, together with esterified and non-esterified cholesterol and other lipids and glycosaminoglycans (Crabb et al., 2002; Malek et al., 2003). Risk factors for AMD include age, sex, family history, APOE genotype, smoking, ethnicity and cardiovascular disease (Seddon, 2001). Genetic factors are implicated in AMD on the basis of twin and family studies but it appears to be a genetically complex disorder (Hammond et al., 2002). [ABSTRACT FROM AUTHOR]

Retinitis Pigmentosa (RP) is a group of disease with progressive degeneration of photoreceptor. Patients present with night blindness, progressive loss of peripheral vision, and pigmentary alterations in the retina with the appearance of "bone-spicules". X-Linked Retinitis Pigmentosa (XLRP) accounts for about 15-30% of all RP cases1-4, and produces severe symptoms, with early onset and rapid deterioration. Five XLRP-related loci, RP2, RP3, RP6, RP23 and RP24, were mapped on the X chromosome through linkage analyses. RP3 and RP2 account for 56-90% and 10-20% of XLRP, respectively.5-9 The two major loci, RP2 and RPGR (RP3) genes, have been cloned successfully.10-13 Retinitis Pigmentosa GTPase Regulator (RPGR), locus on the X chromosome (Xp21.1), accounted for about 30- 60% of XLRP cases in molecular screening studies.13-14 Positional cloning of the RPGR gene originally revealed a 2784-nucleotide (nt) ubiquitously expressed transcript which include 19 exons coding for 815 amino acids. Exon ORF15 which was identified later, encodes 567 amino acids, and was shown to be a mutation hot spot. Disease-causing mutations reported so far are localized in 5-prime exons and ORF15, while none have been reported in exons 16-19. The N-terminal sequence of RPGR spanning exons 1-11 shows homology to the regulator of chromatin condensation (RCC1)10, a nuclear protein that catalyzes guanine nucleotide exchange for the small GTPase Ran and regulates nuclear import and export.15 On the basis of RCC1 crystal structure, the RPGR protein is predicted to have a seven-blade beta-propeller structure and to function as a GEF for a small GTP-binding protein. The mutations exclusively affect the RCC1-like domain (RLD) of RPGR and ORF15, which suggests that these regions are contribute to the physiological role of RPGR in the retina. Although a growing number of novel mutations of RPGR are being reported, its function in vivo is still unclear. Through a yeast two-hybrid screens, two proteins, the delta subunit of rod cyclic GMP phosphodiesterase (PDEδ) and RPGR interaction protein (RPGRIP1), were identified to interact with the RLD of RPGR.16-18 [ABSTRACT FROM AUTHOR]

Leber congenital amaurosis (LCA, MIM 204000) is the earliest and most severe form of all hereditary retinal dystrophies, responsible for congenital blindness. Its frequency, estimated until recently to 5% of all inherited retinal dystrophies1, has been re-evaluated as some LCA cases might represent the extreme end of a spectrum of severity of retinal dystrophies.2-4 [ABSTRACT FROM AUTHOR]

Genetically determined optic atrophies (OA) affect the retinal ganglion cells, the retinal fibre layer or the intra-ocular portion of the optic nerve. Autosomal dominant optic atrophies (DOA) are the most common form of hereditary optic neuropathy (prevalence 1 : 50,000). The genetic heterogeneity of DOA has been demonstrated. Three loci have been reported: OPA1 [3q28-q29; MIM 165500], OPA4 [18q12.2-q12.3; MIM 605293, and OPA5 (22q12.1-q13.1)1. OPA1 which accounts for about 90% of DOA is due to mutations in the Msp1 protein [MIM 605290]. [ABSTRACT FROM AUTHOR]

Leber congenital amaurosis (LCA) is the most early and severe form of all inherited retinal dystrophies, responsible for congenital blindness. The genetic heterogeneity of LCA has been accepted for a long time but it turned out to be largely higher than all odds. So far, 11genes have been mapped on human chromosomes and eight identified. i) the retinal specific guanylate cyclase gene (GUCY2D, retGC1; 17p13.1; LCA1; MIM 600179), ii) the gene encoding the 65-kD protein specific to the retinal pigment epithelium (RPE65; 1p31; LCA2; MIM180069), iii) the cone-rod homeobox-containing gene (CRX; 19q13.3; LCA7; MIM 60225), iv) the gene encoding the arylhydrocarbon receptor interacting protein-like 1 (AIPL1; 17p13.1; LCA; MIM 604392), v) the gene encoding the retinitis pigmentosa GTPase regulator-interacting protein 1 (RPGRIP1; 14q11; LCA6; MIM 605446), vi) the human homologue of the drosophila melanogater crumbs gene (CRB1; 1q31; LCA8; MIM 604210), vii) the gene encoding the tubby-like protein 1 (TULP1; 6q21.3; LCA10; MIM 602280), viii) the retinol dehydrogenase 12 (RDH12; 14q24; LCA11; MIM 608830), ix) LCA3 (14q24; MIM 604232), x) LCA5 (6q11-16; MIM 604537) and xi) LCA9 (1p36; MIM608553). [ABSTRACT FROM AUTHOR]

Factors modifying clinical expression of inherited diseases are likely to be complex, involving genetic factors, environmental factors and stochastic effects. One way to reduce the complexity is to focus on individuals who share a dominant mutation identical by descent, thus eliminating variability in the underlying mutation and variation in cis to the mutation. A further simplification is to limit analysis to a single, extended family, which may reduce, though not eliminate, environmental effects. [ABSTRACT FROM AUTHOR]