Cystic fibrosis is caused by an inability to transport chloride ion
across cellular membranes. Once upon a time people diagnosed CF in
babies by licking them - very salty tasting babies had CF (no lie!).
KidsHealth for Parents: Cystic Fibrosis
"In CF, the inherited CF gene directs the body's epithelial cells to
produce a defective form of a protein called CFTR (or Cystic Fibrosis
Transmembrane Conductance Regulator) found in cells that line the
lungs, digestive tract, sweat glands, and genitourinary system. When
the CFTR protein is defective, epithelial cells can't regulate the way
chloride (part of the salt called sodium chloride) passes across cell
membranes. This disrupts the essential balance of salt and water that
is needed to maintain a normal thin coating of fluid and mucus inside
the lungs, pancreas, and passageways in other organs. The mucus
becomes thick, sticky, and hard to move."
Cystic Fibrosis Foundation: Sweat Testing
"Children and adults with CF have an increased amount of sodium and
chloride (salt) in their sweat. In general, sweat chloride
concentrations less than 40 mmol/L are normal (does not have CF);
values between 40 to 60 mmol/L are borderline, and sweat chloride
concentrations greater than 60 mmol/L are consistent with the
diagnosis of CF. For individuals who have CF, the sweat chloride test
will be positive from birth."
National Human Genome Research Institute: Learning about Cystic Fibrosis
"In normal cells, the CFTR protein acts as a channel that allows cells
to release chloride and other ions. But in people with CF, this
protein is defective and the cells do not release the chloride. The
result is an improper salt balance in the cells and thick, sticky
To answer this question I went to the MedlinePlus
(www.medlineplus.gov) Health Topic for Cystic Fibrosis:
http://www.nlm.nih.gov/medlineplus/cysticfibrosis.html. I knew to go
to that health topic because of my professional specialty as a medical
librarian (and I've used CF in teaching examples so knew its cause).
Please let me know how I can help further, or if anything needs clarifying!