I have these same exact mutations, and while I'm not a geneticist, I do understand a little bit about genes and about the prognosis ("mild CF" or CRMS).
For heterozygous R117h mutation and it's relationship with the variants of the polythimidine tracts, the variants aren't on the same part of the gene, nor are they CF mutations, but they have a relationship with how the mutated gene functions. It offers some "helper" functionality, collaborating; it kind of offers some repair assistance with the CFTR channel, but it only partially does the job, kind of like fixing something with duct tape. It sort of works, most of the time, causing only mild symptoms, but it doesn't work so well as you get older, when things start falling apart in our bodies in general (this is why this particular mutation is really more of a concern for adults with it). The 3 variants they look at with R117h are 5T, 7T, and 9T. I might have it backwards, but I think 5T is the worst, 7T is in the middle, and 9T is the best. The R117h with 5T have the biggest chance of developing full-blown CF. So, having 7T as homozygous just means that it shows up on both gene copies, even though R117h is heterozygous, just showing up on one gene copy; these are 2 different gene areas that just happen to work together. It's the R117h that is the mutation, and the other one is the helper that makes it better. Does that make sense?
For the prognosis, you're lucky that this is a mild mutation that only gets bad when hitting middle age or when other aspects of health might start going downhill in general (think holistically). That said, you still have to be diligent about respiratory infections, but his outlook for childhood should be relatively "normal." Before the "mild CF" becomes ACTUAL CF, it's known as CRMS, or Cystic Fibrosis Related Metabolic Syndrome. Some people with CRMS will develop full-blown CF in adulthood; case reports of people with these mutations usually show people finding out in their 50's and 60's when they begin to develop serious lung issues. This is what I have, and I'll be 44 years old in January. I found out when I was pregnant through genetic screening; my son is OK, but I was surprised to find that I had the mutations. I was lucky enough to grow up on a farm and have a healthy lifestyle, but I did have bronchitis about once a year and walking pneumonia once as a kid. I also had pancreatitis twice as an adult, but no real digestive issues other than occasional reflux and a touch of IBS (irritable bowel syndrome). My lungs were brilliantly clear most other times, and it wasn't until I was in my late 30's that I developed a light chronic cough. I had just started going to a CF clinic then, as it was a couple of years after finding out, and they tested my sputum positive with MAI, which is a non-tuberculosis mycobacterium. MAI is a bit alarming as it's notoriously difficult to treat, and it's just about everywhere, including your shower head, where it can aerosolize and enter the lungs. Most people are immune to MAI, but if you're a good host, as I am, and I'm sure your son will eventually be, it will grow in your lungs just like tuberculosis. It will come back after treatment because it's everywhere, so the best option is to stay as healthy as possible to let your immune system fight it. Luckily, I'm having great success with taking Kalydeco, and my cough has gone down to nearly nothing, and I only show any MAI on DNA probe samples - I just don't make enough of it to really show up as a blob in my sputum anymore. I know that the Kalydeco is horrendously expensive for your insurance, but it WORKS for these mutations, and it will prevent your son developing any bad germ colonies. I wouldn't wait until he gets sick to start, as it's hard to change a bacterial colony; you want to invite the healthy flora to reside, rather than the bad flora. This medicine has truly been amazing for me; your son might be able to go completely symptom-free on Kalydeco, other than needing fertility help if he ever wants kids. For other prevention from the MAI, I would recommend getting a shower head that doesn't have an air chamber to grow the bacteria, like this one:
http://www.highsierrashowerheads.com. Otherwise, you'll have to soak your shower head in vinegar every 3 months. Also, make sure your son is athletic, so he grows strong lungs; cardio workouts do wonders for airway clearance. I can't recommend the Kalydeco and exercise enough - you're very lucky to have found out early, as he has a chance of a very healthy life.
