onset is about six months. >> wow. >> so if your partner has it and you were to have another child -- >> my kid could have it. >> yeah. >> how would i change that gene? >> we'll look at the hexasequence here and look at the particular mutation. here's the error. >> wow. >> literally that's the one letter that's wrong? >> yes. it's a screw-up. we're going to print out the correct copy. >> that's nuts. how would i get that into my body to fix that problem? >> there's viruses. there's hijacking your immune system. but currently the technology is not i think really good enough. we need to make ways that are much safer, that don't result in problems like your immune system going crazy -- >> shutting down? >> exactly. we don't want that. >> no. >> we're going to show you how we make the dna. all life comes from four chemicals. there's an a, c, there's a t, and there's a g. we take code sent us and we turn it into physical a, t, c, g