Hi again Marie,
Colleen is correct saying that there are no levels of severity or stages of CF. However, I remembered seeing classifications of mutations awhile back. I asked our CF team if these classifications were valid scientifically and they said yes. I searched this tonight and this is what I found:
Cystic fibrosis mutations can be classified by the molecular mechanisms by which they cause dysfunction (Table 3-30) (Kerem and Kerem, 1996; Rosenstein and Zeitlin, 1998; Mickle and Cutting, 1998; Mickle and Cutting, 2000; Zielensky, 2000). Mutations can result in CFTR that is absent, reduced, or abnormally functioning. These are grouped, as follows:
· Class I mutations (e.g., G542X, 621+1G>T, and 711+1G>T) result in total deficiency or unstable/non-functional CFTR protein.
· Class II mutations (e.g., delF508, N1303K, and delI507) disrupt normal intracellular processing (e.g., glycosylation), causing instability of CFTR protein, or interfering with its movement to the correct cellular location.
· Class III mutations (e.g., G551D) result in a normal amount of CFTR protein being produced and positioned at the cell surface, but the protein is non-functional.
· Class IV mutations (e.g., R117H, A455E) result in a normal amount of functional CFTR at the cell membrane, but chloride conductance is reduced. These mutations are generally associated with a pancreatic sufficiency.
· Class V mutations (e.g., 3849+10KbC>T)result in reduced levels of normally functional CFTR protein at the cell membrane and are also associated with a less severe phenotype.
They made it clear that these classifications cannot predict severity, but that those in class I, II and III usually have pancreatic insufficiency and lung involvement. While those in IV and V may have pancreatic sufficiency and sometimes a milder course. I think it would also depend on your combination of mutations. For ex, you might have a class I with a class V.
Hope this gives some additional info.
Maria (mother of three daughters, the youngest Samantha w/cf)