Negative sweat test, positive genetics

[anonymous]

Anyone here diagnosed despite a negative sweat test (and I mean very clearly negative like 30 or below??) If so, which genes do you have, and did they show up on the genzyme panel that shows the most common 87 genes or just on the ambry panel?
Thanx!

 

[serendipity730]

Hello,
Hello, I was diagnosed long before genotyping came into existence, but it is undoubtedly more reliable than the sweat test. If the results were the other way around ( neg. genetics, pos. sweat test.) I would say that your child has an unknown mutation. What mutation was it, by the way?
Mary

 

[anonymous]

hi

there are different classes of mutations of the cystic fibrosis gene. it could be possible that, in your case, less severe types of mutations have been found.

class 1 mutations are supposed to be the most severe type of mutation as the cystic fibrosis gene is not produced at all due to the mutation - examples are 1717-1G->A, G542X, W1282X and R553X.

some, e.g. deltaf508 and N1303K, are functional but do not travel to the correct position of the cell membrane and therefore can't transport chloride ions out of cells. these are class 2 mutations (supposedly slightly less severe)

class 3 mutations like G551D, cause a block in regulation of the cftr protein (the product of the cf gene). cf is, again slightly less severe.

class 4 mutations cause reduced conductance of the protein - slightly less severe again - mutations such as R117H and R347P. people with this mutation don't have digestive problems (also - occasionally, sweat tests are neg.)

with class 5 mutations, the protein is sometimes functional and sometimes not. these type of mutations normally give a neg. sweat test result and sometimes aren't classed as a cf diagnosis because the symptoms are minimal. these mutations include A445E.

it is possible that, in your case, only class 5/class 4 mutations have been found and therefore a neg sweat test.

hope this info helps.