Steph - since you were tested and found to be a carrier I would assume the D508 that your son has came from you. <b>IF</b> your son has CF he would have gotten a less common mutation from your husband since your hubby was tested and it didn't show one of the more common mutations. The test they gave your husband probably only covered a few mutations, but it definately would have covered the D508. In order to have CF you need two mutations and you get one from the Dad and one from the Mom - they can be the same mutation, but they could also be two different ones. I would say you have the odds on your side though if they are telling you only a 4% chance. Good luck and I hope they can get you answers ASAP.