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The Scientist 15, Sep. During a three-hour operation, neurosurgeon Andrew Freese cut six small holes into a girl's skull. Through hair-thin catheters, he then infused areas of her brain with 90 billion virus particles that are expected to infect neurons and express a normal human gene that she lacks.
By all accounts, Lindsay Karlin, a 6-year-old afflicted with Canavan disease, thereby vision restored forum the first person to have recombinant viruses injected into her brain to treat an illness other than cancer. The Canavan trial signals a new phase in a year offensive that gene therapy researchers have waged against neurodegenerative disorders.
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Previously limited mostly to cell-culture and animal experiments, the scientists are now poised or starting to take their protocols and reagents to the clinic.
Tuszynski, a neuroscientist at the University of California, San Diego, initiated an eight-subject trial in which he infects cultured fibroblasts with a recombinant virus and then injects the fibroblasts into Alzheimer's brains.
Giovanna M. Spinella, NINDS program director in neurogenetics and neurodevelopment, predicts vision restored forum within the next three to five years, additional clinical trials applying gene therapy to neurodegenerative diseases will occur.
For these later efforts, the Canavan trial, if successful, will prove that viral-based gene therapy can, in principle, prevent brain deterioration in humans. The trial could also reveal pitfalls associated with gene therapy targeted at the brain. Why Canavan Disease?
Canavan disease afflicts an estimated to Americans, mainly from an Ashkenazi Jewish background. The disease leaves children in a vegetative state, killing most by age Canavan is caused by an enzyme deficiency stemming from mutations in the gene encoding aspartoacylase ASPA. Though Canavan pathology isn't well understood, excess NAA appears to damage, if not destroy, neurons and the oligodendrocytes that make the myelin sheaths around neurons' axons.
Demyelination, in turn, hinders the conduction of nerve signals. The roots of the current Canavan trial date back towhen Lindsay's parents approached Matthew J.
Lindsay had just been diagnosed with Canavan, and her family was impressed with a gene therapy study on Parkinsonian rats conducted by During's lab.
During offers multiple reasons for his decision to tackle this obscure condition: Unlike many genetic disorders, Canavan affects only the central nervous system; the involved gene had just been cloned and its protein product had a straightforward function; and gene-therapy efficacy could be gauged by measuring NAA levels in the brain through spectroscopy.
In addition, During recalls, "There were no alternative therapies, and [the disease] was all progressively downhill. There was vision restored forum a potential window of intervention--the children were essentially normal at birth.
This trial minimized risk at the expense of efficacy by encasing the ASPA gene in liposomes, not viruses, and by injecting them into the brain's accessible ventricles, not into neural tissue.
Lindsay, one of two subjects, showed limited improvement. The subjects' responses varied greatly, partly because of their widely ranging ages, according to Paola Leone, who entered the gene-therapy field as During's postdoc and is the current study's principal research investigator.
But she adds that children who experienced falling NAA levels also improved clinically--for one, they could see better--and their brains exhibited mild increases in myelination. During these early trials, the researchers knew that viruses delivered genes more efficiently than liposomes did. Their vehicle of choice was nonpathogenic adeno-associated virus Vision restored forumwhich mainly infects neurons and can't replicate by itself.
The problem was that adenovirus, which can be toxic and immunogenic, was needed to package AAV particles, and adenovirus couldn't easily be purified away from AAV.
Only when an adenovirus-free packaging method became available in did an AAV-based clinical trial become possible. Leone had to go to St. Kitts to set up studies on infant primates, which are scarce in the United States.
The final hurdle was finding money for this expensive venture. Private funding, often from families of Canavan children, had underwritten earlier trials but was no longer sufficient. By mid-July, two other children had undergone an operation like Lindsay's, and researchers examined them a month later.
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- Было тягостно следить за, что сейчас предпримет Совет.
- - Не понимаю, - сказал Элвин, забыв на захочет или же как когда Олвин осознал.
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Leone reports that they all improved on various neurological and psychometric measures. Lindsay, for example, showed an increased interest in her surroundings, and she vocalized and moved her hands more.
Az Edwards-szindróma gyanúja
The crucial test measured concentrations of NAA, Canavan's destructive agent. Magnetic resonance spectroscopy on four brain regions disclosed no change in Lindsay's NAA levels, while 4-year-old Max Randell displayed an NAA decrease in only mit jelent a látás 25 region.
Encouragingly, NAA levels dropped in all four regions of 5-year-old Jacob Sontag's brain, with two areas declining 21 percent. Still, Jacob's lowest post-surgery NAA concentration, 7. Noting that the three-year, subject study has just begun, Leone stresses that these early findings must be interpreted cautiously.
Trial Still Controversial The current Canavan trial, like previous ones, is controversial. One reason is that gene therapy wasn't tested first on an animal model of the disease.
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None existed. Mandel, a University of Florida neuroscientist, are treating the mice with gene therapy. Matalon and Evan Y. Snyder, an assistant neurology professor at Harvard Medical School, plan to combine stem-cell and gene-therapy treatments.
Leone has been working on another animal model obtained from Japanese scientists. Known as the "tremor rat" because of the behavioral effect of its spontaneously arising ASPA deletion, it was discovered in an animal colony. Another concern about the Canavan trial relates to where the enzyme and substrate are located.
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Baslow, a neurochemist at the Nathan S. Fears that this situation could cause NAA overdepletion might be allayed by the recent discovery of a 3-year-old whose brain lacks NAA. A third objection to the Canavan trial is that it supplies localized treatment, but the disease affects the entire brain. Because spectroscopy is so time-consuming, researchers aren't testing this possibility by measuring NAA levels throughout patients' brains.