Carriers are somewhat resistant to dehydration due to diarrhea from diseases such as cholera and dysentery. So they had her egg cells fertilized in vitro by his sperm cells. The resulting fertilized eggs were then tested by PCR to determine if they contained the normal or mutant genes. Over 2 million bp with 75 exons that code for protein of 4,000 a.a. Used in a nasal spray.
Good gene is incorporated into lung cells.