Transplacement mutagenesis: a novel in situ mutagenesis system using phage-plasmid recombination.
(1/2258)
Site-specific mutagenesis provides the ability to alter DNA with precision so that the function of any given gene can be more fully understood. Several methods of in vitro mutagenesis are time-consuming and imprecise, requiring the subcloning and sequencing of products. Here we describe a rapid, high fidelity method of in situ mutagenesis in bacteriophage lambda using transplacement. Using this method, mutations are transferred from oligonucleotides to target phages using a plasmid interface. A small (50 bp) homology region bearing a centred point mutation is generated from oligonucleotides and subcloned into a transplacement plasmid bearing positive and negative phage selectable markers. Following a positive/negative selection cycle of integrative recombination and excision, the point mutation is transferred precisely from plasmid to phage in a subset ( approximately 25-50%) of recombinants. As the fidelity of both oligonucleotide synthesis and phage-plasmid recombination is great, this approach is extremely reliable. Using transplacement, point mutations can be accurately deposited within large phage clones and we demonstrate the utility of this technique in the construction of gene targeting vectors in bacteriophages. (+info)
Prospective cohort study of antioxidant vitamin supplement use and the risk of age-related maculopathy.
(2/2258)
In a prospective cohort study, the authors examined whether self-selection for antioxidant vitamin supplement use affects the incidence of age-related maculopathy. The study population consisted of 21,120 US male physician participants in the Physicians' Health Study I who did not have a diagnosis of age-related maculopathy at baseline (1982). During an average of 12.5 person-years of follow-up, a total of 279 incident cases of age-related maculopathy with vision loss to 20/30 or worse were confirmed by medical record review. In multivariate analysis, as compared with nonusers of supplements, persons who used vitamin E supplements had a possible but nonsignificant 13% reduced risk of age-related maculopathy (relative risk = 0.87, 95 percent confidence interval (CI) 0.53-1.43), while users of multivitamins had a possible but nonsignificant 10% reduced risk (relative risk = 0.90, 95% CI 0.68-1.19). Users of vitamin C supplements had a relative risk of 1.03 (95% CI 0.71-1.50). These observational data suggest that among persons who self-select for supplemental use of antioxidant vitamin C or E or multivitamins, large reductions in the risk of age-related maculopathy are unlikely. Randomized trial data are accumulating to enable reliable detection of the existence of more plausible small-to-moderate benefits of these agents alone and in combination on age-related maculopathy. (+info)
Retinal stimulates ATP hydrolysis by purified and reconstituted ABCR, the photoreceptor-specific ATP-binding cassette transporter responsible for Stargardt disease.
(3/2258)
Many substrates for P-glycoprotein, an ABC transporter that mediates multidrug resistance in mammalian cells, have been shown to stimulate its ATPase activity in vitro. In the present study, we used this property as a criterion to search for natural and artificial substrates and/or allosteric regulators of ABCR, the rod photoreceptor-specific ABC transporter responsible for Stargardt disease, an early onset macular degeneration. ABCR was immunoaffinity purified to apparent homogeneity from bovine rod outer segments and reconstituted into liposomes. All-trans-retinal, a candidate ligand, stimulates the ATPase activity of ABCR 3-4-fold, with a half-maximal effect at 10-15 microM. 11-cis- and 13-cis-retinal show similar activity. All-trans-retinal stimulates the ATPase activity of ABCR with Michaelis-Menten behavior indicative of simple noncooperative binding that is associated with a rate-limiting enzyme-substrate intermediate in the pathway of ATP hydrolysis. Among 37 structurally diverse non-retinoid compounds, including nine previously characterized substrates or sensitizers of P-glycoprotein, only four show significant ATPase stimulation when tested at 20 microM. The dose-response curves of these four compounds are indicative of multiple binding sites and/or modes of interaction with ABCR. Two of these compounds, amiodarone and digitonin, can act synergistically with all-trans-retinal, implying that they interact with a site or sites on ABCR different from the one with which all-trans-retinal interacts. Unlike retinal, amiodarone appears to interact with both free and ATP-bound ABCR. Together with clinical observations on Stargardt disease and the localization of ABCR to rod outer segment disc membranes, these data suggest that retinoids, and most likely retinal, are the natural substrates for transport by ABCR in rod outer segments. These observations have significant implications for understanding the visual cycle and the pathogenesis of Stargardt disease and for the identification of compounds that could modify the natural history of Stargardt disease or other retinopathies associated with impaired ABCR function. (+info)
Central corneal endothelial guttae and age-related macular degeneration: is there an association?
(4/2258)
The similarities between the corneal endothelium and retinal pigment epithelium in terms of their embryology, barrier function and predilection to age-related degeneration prompted this investigation into a possible association between central corneal guttae (CCG) and age-related macular degeneration (ARMD). 50 patients with clinically significant CCG were prospectively evaluated for the presence of ARMD. 51 age-matched patients attending for unrelated ailments who did not have CCG were also evaluated for the presence of drusen and other signs of ARMD. Of the 50 patients with CCG, 23 had bilateral ARMD and 4 had unilateral ARMD. In the control group, 9 patients had bilateral and 4 had unilateral ARMD. There was significant difference in the prevalence of ARMD between patients with CCG and those with no CCG (p = 0.017 and p < 0.001 for right and left eyes respectively). We found an association between CCG and ARMD. The presence of CCG in a patient may imply increased risk for the presence of ARMD. In a patient with CCG requiring cataract or corneal surgery, the successful outcome may be compromised by the presence of ARMD. (+info)
A new locus for autosomal dominant stargardt-like disease maps to chromosome 4.
(5/2258)
Stargardt disease (STGD) is the most common hereditary macular dystrophy and is characterized by decreased central vision, atrophy of the macula and underlying retinal-pigment epithelium, and frequent presence of prominent flecks in the posterior pole of the retina. STGD is most commonly inherited as an autosomal recessive trait, but many families have been described in which features of the disease are transmitted in an autosomal dominant manner. A recessive locus has been identified on chromosome 1p (STGD1), and dominant loci have been mapped to both chromosome 13q (STGD2) and chromosome 6q (STGD3). In this study, we describe a kindred with an autosomal dominant Stargardt-like phenotype. A genomewide search demonstrated linkage to a locus on chromosome 4p, with a maximum LOD score of 5.12 at a recombination fraction of.00, for marker D4S403. Analysis of extended haplotypes localized the disease gene to an approximately 12-cM interval between loci D4S1582 and D4S2397. Therefore, this kindred establishes a new dominant Stargardt-like locus, STGD4. (+info)
ATP binding cassette transporter retina genotypes and age related macular degeneration: an analysis on exudative non-familial Japanese patients.
(6/2258)
AIM: To determine whether mutations in the Stargardt's disease gene, ATP binding cassette transporter retina (ABCR) affect the occurrence of age related macular degeneration (AMD) in Japanese non-familial patients. METHODS: 80 unrelated Japanese patients with AMD (67 males and 13 females; mean age, 67.2 years) diagnosed by indocyanine green angiography and 100 age matched control subjects were studied. Among the AMD patients, 70 (87.5%) had choroidal neovascularisation of exudative type. Genomic DNA was purified from the total blood and 10 exons (exons 11, 23, 29, 32, 34, 37, 41, 43, 44, and 49) that have been reported to contain AMD associated mutations were amplified by polymerase chain reaction (PCR). The amplicons were analysed by the single strand conformation polymorphism (SSCP) method. The nucleotide sequencing of the amplicons was determined when necessary. RESULTS: Of the 10 exons, aberrant patterns of SSCP were detected in three exons-exons 29, 41, and 43. In exon 29, an aberrant pattern was found in seven of 80 patients (8.8%) and eight of 100 controls (8%). Sequencing of the PCR products revealed a heterozygous T1428M mutation which has been previously reported as one of the AMD associated mutations. Statistical analysis showed that there was no significant difference in the occurrence of this mutation between these AMD patients and the control groups (p = 0.86). In exons 23, 41, and 43, polymorphisms and sequence variations were found. CONCLUSION: No data to support the association between the ABCR gene mutations and AMD of Japanese patients, especially that of the exudative type, were obtained in this molecular genetic analysis. (+info)
Radiotherapy for isolated occult subfoveal neovascularisation in age related macular degeneration: a pilot study.
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BACKGROUND/AIMS: Teletherapy has been proposed as a possible treatment for choroidal neovascular membranes (CNV), secondary to age related macular degeneration (AMD) not amenable to laser photocoagulation. The aim of this prospective study has been to investigate the effect of teletherapy on isolated occult choroidal neovascular membranes of subfoveal location. METHODS: 28 AMD patients presenting with retrofoveal isolated occult CNV demonstrated by fluorescein angiography were treated by external beam radiation. A complete ophthalmological examination, fluorescein angiography, and indocyanine green angiography (ICG) were performed within 15 days before treatment and repeated at follow up. A total dose of 16 Gy was applied in four sessions of 4 Gy using a 4 MeV photon beam. Follow up ranged from 6 to 9 months (mean follow up 6.4 months). RESULTS: Visual acuity was found to be stable in 68% of the cases. The decrease in visual acuity was of 3-6 lines in 18% and of more than 6 lines in 10% of the eyes at last examination. On fluorescein angiography the size of the lesion area was found to be stable in 67%, decreased in 13%, and increased in 20% of the cases. On ICG angiography the size of the CNV was stable in 93% and increased in 7% of the cases. All the eyes experiencing a visual acuity decrease showed either no change or an increase in size of the membrane on fluorescein angiography and/or on ICG. CONCLUSION: According to this study with strict inclusion criteria, external beam radiotherapy seems to have a beneficial effect on the evolution of isolated occult subfoveal CNV. (+info)
North Carolina macular dystrophy: clinical features, genealogy, and genetic linkage analysis.
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PURPOSE: To study the North Carolina macular dystrophy phenotype (MCDR1) in multiple families of different ethnic backgrounds, to determine the genetic relationships of these families, and to determine the minimal candidate region of the MCDR1 gene. METHODS: Thirteen families with the North Carolina MCDR1 were ascertained. These families were of various ethnic and geographic origins, such as Caucasian, Mayan Indian, African American, French, British, German, and American. Extensive genealogical investigations were performed for all families. A total of 232 members of these families underwent comprehensive ophthalmic examinations, including blood collection for genotyping. Of these, 117 were found to be affected with the disorder. Genetic linkage simulation studies were performed using the computer program SIMLINK. Two-point linkage analysis, haplotype analysis, and multipoint linkage analyses were performed using the computer programs M-LINK, VITESSE, and FASTLINK. RESULTS: The clinical features were consistent with the diagnosis of North Carolina macular dystrophy in all families studied. Multipoint linkage analysis and haplotype analysis indicate that the MCDR1 gene is in the 1.1-centimorgan (cM) interval between the genetic markers D6D249 and D6S1671, with a maximum LOD score of 40.03. There was no evidence of genetic heterogeneity. Families 765, 768, 772, 1193, and 1292 shared the same chromosomal haplotype in this region, suggesting they are the result of the same ancestral mutation. The remaining families each likely represent independent origins of the mutation in the MCDR1 gene. North Carolina macular dystrophy is present worldwide and does not emanate from a single founder from North Carolina. (+info)