We're seeing an illustration of that this week. In March of last year, Editas started treating patients who have Leber’s congenital amaurosis 10 (LCA10), which is an incurable condition leading to childhood blindness. It's rare (2 to 3 out of every 100,000 births), and it's been found over the years to be due to mutations in the gene coding for the CEP290 protein. That one appears to be involved in formation of the primary cilium structure in the photoreceptor cells of the retina, perhaps by being a connection between microtubules in these cells and the proteins on the cell surface. If you would like to experience that feeling I mentioned of being outnumbered by the things that we don't know, try to imagine how you would predict the cause of LCA10 without having any of these genetic studies to help you out - or alternatively, try to imagine being given the CEP290 protein and then being asked to predict what diseases you might expect to occur if its structure were disrupted. We're a long way from being to do either of those. As it is, we end up learning a lot about individual genes and proteins by tracking down their associations with such rare conditions.

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