Cystic fibrosis (CF), a common genetic disease that causes severe lung disease and other symptoms, has two forms: classic and nonclassic, or atypical. People with the atypical form of cystic fibrosis can have the same symptoms as a person with the classic form; however, the symptoms are generally mild and may only have some, but not all, of the features. Doctors will often diagnose atypical cystic fibrosis based on the results of a sweat chloride test--a test that measures the amount of sodium chloride in sweat.
Lung Disease
Classic cystic fibrosis is mainly characterized by severe lung infections, beginning in infancy or early childhood. In the atypical form, lung disease may not form until later in childhood; however, this is not always the case since newborn screening does not always identify infants with atypical CF. Recurrent infections, such as pneumonia, cause scar tissue to form in the lungs---causing permanent damage. Some people with atypical forms of CF will have severe lung disease, whereas others may not have this symptom at all
Pancreatic Disease
While most people with atypical cystic fibrosis do not have the same pancreatic problems as people with the classic form, complications still occur. This could be due to poor absorption of nutrients from food, or pancreatitis---an infection that can cause inflammation and scar tissue. In many individuals, recurrent pancreatitis may be the only symptom of CF. Recurrent pancreatitis may be caused by other diseases, but genetic tests that look for changes in the gene for cystic fibrosis are often done to see if a person has CF.
Male Infertility
Most males with cystic fibrosis are born without a body structure called the vas deferens, a condition called congenital bilateral absence of the vas deferens, or CBAVD. As the vas deferens is a tube that carries sperm from the testes, most men with CF are infertile. Men with atypical CF may only have CBAVD and show no other symptoms of CF, while others may have some lung or pancreatic symptoms. Testing for changes in the cystic fibrosis gene is commonly done in males being treated for infertility.
Borderline or Mildly Elevated Chloride Sweat Test
The main distinguishing feature of classic CF and atypical CF is the chloride sweat test value. A sweat test measures the amount of chloride secreted in a person's sweat over time. People with atypical CF may have several features of classic CF, but if their chloride sweat test is only mildly elevated or borderline, they are diagnosed with atypical cystic fibrosis. The amount of chloride in the sweat of people with classic CF is very high.
