Thanks for noting the exact wording. I was able to locate it in the CFTR Database and it has been analyzed as to it's biochemistry but I'm not coming up with any research on how it operates, or impacts the patient . With ~2,000 CFTR mutations and now polymorphisms like 7T/7T and such, the genetic combinations have expanded geometrically. The virulence of the variant is going to be seen in your son and he may be the first. The most common and the worst mutations have been a priority and hopefully that means he's not going to have issues because they haven't gotten to it.
More important is his heterozygous status, meaning that he has just one mutation, or variant as they call it. Understand that nothing is absolute in genetics. In the majority of people who have CF, they have a mutation, or something acting like one, plus another mutation. In classic terms, having the same mutation on both chromosomes is homozygous, and is most likely to come with CF issues. We know now that a different CF causing mutation on each of the two chromosomes has a good chance of causing CF. I'm referring to the pairs of chromosomes in each cell.
The 7T/7T polymorphism is known to cause CF of the pancreas and GI tract. He could be a symptomatic carrier, a heterozygous patient with less severe symptoms because of the polymorphism. It's not overly common, but worth keeping it in mind.
I know that you wanted this in plain English. I'll try. Your son has a single copy (heterozygous) of a CFTR mutation T8961, a variant of unknown disease causing ability. It appears that a Poly T variant 7T/7T is associated with this mutation.
I know that a few CFers present pancreatic and GI issues with T polymorphisms. If you have a symptom free child, file this away and move on. Someone thought this was an important test. If he's symptomatic, I'd like to know what is going on. I'm 7T/7T.