(chuckles) four year old annabel frost has a heart-wrenching genetic disorder. le bit about annabel? - when annabel was born, it was such a wonderful moment. but we were in this happy fog and didn't notice the nystagmus. the eye movement. we didn't notice the jerky musc movements we didn't notice any of that, but the doctors realized that something was wrong. - [kondwani] they diagnosed annabel with alternating hemiplegia of childhood or ahc. - hi. - [kondwani] this extremely rare disorder causes debilitating spells of paralysis, delayed development, and life-threatening seizures. - she'd have days of paralysis where her full one side of her body, she'd drag it along behind her as she crawled. - [simon] you know, once a day, she will have these choking episodes where i need to pick her up and hit her on the back to make sure that she could breathe. (ominous music) (dramatic electronic music) - annabel's condition is a result of a problem in her dna. the twisng double helix of dna is made up of four different baseairs or nucleotides. the unique sequence of these b

. - [kondwani] all this makes me think of young annabel frost and her debilitating genetic disorder. this kind of research fills me with hope. in fact, genetic engineering can even remedy genetic disorders like sickle cell anemia. us by mutaon, this diase deforms blood cells into hook-like shapes which can stick together and cause life-threatening blood clots. - crispr's now being used to change genes in sickle cell anemia. where you then transplant back into those patients, cells in the blood system that will essentially reverse the sickle cell disease, and so those types of trials are occurring now with crispr. - [kondwani] recently, scientists gene edited a patients own stem cells that pduce bone marrow. they then re-injected these altered cells back into her body. amazingly, this therapy cured the patient's sickle cell disease for the first time in history. - technologies like crispr are incredibly powerful and n change the world. they also have the potential for changing humanity as itself. - but there are limitations. the crispr technology is not perfect and sometimes it makes