User:Reid K. Honda
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- Reid K. Honda
- Loyola Marymount University
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I work in the Your Lab at XYZ University. I learned about OpenWetWare from Through the professor of my seminar class, Dr. Carl Urbinati, and I've joined because It is required for my Senior Seminar class here at LMU.
- Year, PhD, Institute
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- 2009, BS, Biology, Loyola Marymount University
BIOL 598 Advanced Topics in Gene Expression
I am currently reviewing an article entitled Human gene therapy for RPE65 isomerase deficiency activates the retinoid cycle of vision but with slow rod kinetics
Link to article: 
Link to figure: 
Figure 2B demonstrates that all patients showed a significant increase in light sensitivity in the eyes that were injected with the AAV-based RPE65 gene replacement. The increases were clear in these sets of graphs, which plotted retinal distance against changes in light sensitivity. The “F” in the horizontal axis represented the fovea centralis, a region of the retina composed entirely of cones, which is responsible for a human’s ability to sharply focus on an image. The results suggested that increases in light sensitivity occurred in regions of the retina away from the fovea centralis.
Patient 1 was injected in the inferior retina and showed a significant increase in light sensitivity, as indicated by the stars above the graph. This increase of approximately one log unit occurred about six millimeters away from the fovea. The amount of increase in the three month period following treatment did not significantly change from that of the first month. Patient 2 was injected in the superior retina, and showed an increase in light sensitivity of about two log units, in a region approximately four millimeters away from the fovea. Like patient 1, there was no significant change between the 30-90 days following the treatment. The light sensitivity in patient 3, who was injected in the temporal retina, increased by nearly three log units and covered a larger region of the retina than patient 1 and patient 2. Unlike the first two patients, patient 3 showed a significant increase in certain areas of the retina occurring 60-90 days after treatment.
The control eyes of all three patients (the eyes that were not injected with the gene) all did not show a significant increase in light sensitivity. Test-retest variability obtained from five other patients with the RPE65-LCA disease showed that the magnitude of light sensitivity changes within that group was less than the magnitude of changes in the study eyes. This affirms the fact that the light sensitivity changes in the study eyes were significant.
Link to figure: 
3a A process known as dark adaptation accounts for the fact that human vision becomes more sensitive to light after being in the dark for an extended period of time. An eye can become ten thousand to one million times more sensitive than in regular daylight if allowed to adapt for 20-30 minutes in the dark. Because patients in this experiment reported an increase in light sensitivity in their treated eye after being allowed to sleep in a darkened room, researches repeated the testing after allowing for an extended period of dark adaptation of 3-8 hours. Patients showed gains in light sensitivity of up to 1.3 log units after this extended dark adaptation. These findings suggest that retinoid cycle kinetics in the treated eyes may have been unusually slow.
3b Chromatic sensitivities were measured in the test eyes of patients after being exposed to a desensitizing flash of light. The results of this were used to measure the kinetics of dark adaptation in the treated retinas. The visual function of the cone system returned a minute after the flash. However, rod mediated visual recovery took a lot longer, lasting at least 8 hours. This shows that rod mediated recovery took an unusually long time.
3c This figure compares the light sensitivity of normal eyes to those of pretreated eyes, treated eyes after standard dark adaptation, and treated eyes after an extended period of dark adaptation. Treated eyes that were allowed to undergo extended dark adaptation showed a significant improvement in light sensitivity, and a greater improvement than standard dark adaptation. This shows that treatment with AAV-based RPE65 gene replacement caused a significant increase in the light sensitivities of eyes affected with Leber congenital amaurosis.
Link to figure: 
Aside from the malfunction in the retinoid cycle, the visual loss associated with RPE65-LCA (Leber Congenital Amaurosis) is also due to degeneration of the retinal photoreceptors. The researchers hypothesized that gene therapy would be able to repair the visual loss due to the malfunction of the retinoid cycle, but that it would not be able to repair the loss of cells as a result of photoreceptor degeneration. In order to test this, the researchers first verified that patients with RPE65-LCA had photoreceptor degeneration. Figure 4A consists of retinal cross-sectional images that show the photoreceptor layer (labeled ONL, outer nuclear layer, on the figure) for patient 1 and patient 2 to be significantly thinner than that of a normal person.
Figure 4B shows the relationship between rod sensitivity loss and photoreceptor layer thickness. Both patient 1 and patient 2 displayed increases in rod sensitivity without increases in ONL thickness. Sensitivity loss before treatment for patient 1 and patient 2 were 7.2 and 6.4 log units, respectively (shown as white square and white circle on figure). After treatment, patient 1 gained 2.3 log units in rod sensitivity, and patient 2 showed an improvement of 4.8 log units (shown as grey square and grey circle on figure). Therefore, the researchers concluded that gene therapy has the potential to restore the defective retinoid cycle component of RPE65-LCA, but not the component of photoreceptor degeneration.
- Interest 1
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- Interest 3
- Goldbeter A and Koshland DE Jr. An amplified sensitivity arising from covalent modification in biological systems. Proc Natl Acad Sci U S A. 1981 Nov;78(11):6840-4.
- JACOB F and MONOD J. Genetic regulatory mechanisms in the synthesis of proteins. J Mol Biol. 1961 Jun;3:318-56.
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