Reviewed by Sara Brayshaw, MS, RN Jerry A. Nick, MD

What is Cystic Fibrosis?

Cystic fibrosis (CF) is a genetic disease that primarily affects the lungs and digestive system of about 30,000 children and adults in the United States (more than 70,000 worldwide). The underlying abnormality is the abnormal transport of salt and water across cells, leading to unusually thick, dehydrated and sticky mucus in many tissues of the body, including the airways, pancreatic ducts, sweat ducts, sinuses and bowels.

Obstruction of the pancreatic ducts severely damages the pancreas and results in reduced capacity to make the enzymes required to digest proteins and fat. Individuals with CF are typically diagnosed in infancy by newborn screening. Cystic fibrosis symptoms in infants can include diarrhea and malnutrition. Obstruction of the small airways of the lung results in the permanent dilation of these bronchi (bronchiectasis), and provides a site where certain infections can take hold. The thick and dehydrated mucus prevents the normal clearance of bacteria and other microbes from the lungs, ultimately resulting in chronic infections with specific pathogens.

The most important complication of CF is progressive destruction of the lungs, which results in respiratory failure and death in approximately 80 percent of CF patients. Fortunately, steady advances in medical treatments for cystic fibrosis have provided a range of therapies to slow or prevent complications, resulting in extended lifespan and improved quality of life for children and adults with CF.

 

How Common Is Cystic Fibrosis?

There are about 30,000 people with CF in the United States, and more than 70,000 people worldwide. Between 800 to 1,200 new cases are diagnosed each year in the United States alone (about 1 out of every 3,500 newborns) [2].

Cystic fibrosis (CF) is a genetic disease caused by a mutation in a gene named the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR mutation is extraordinarily common in the general population, with approximately 10-12 million carriers in the United States. Worldwide, prevalence of the CFTR mutation varies greatly between ethnic groups, with the greatest frequency in European-derived populations and Ashkenazi Jews. Estimates of carrier rates and disease prevalence in the United States are listed in below. In some regions of Europe, an even greater carrier rate has been reported.

 

Estimated Prevalence of CFTR Mutations and new cases of Cystic Fibrosis in the United States

Ethnicity Carrier rate Newborns with CF
Caucasian Americans 1 in 29 1 in 3,200
Hispanic Americans 1 in 46 1 in 8,500
African Americans 1 in 65  1 in 17,000
Asian Americans 1 in 90 1 in 31,000
Overall US population 1 in 31  1 in 3500

 

Many scientists have questioned why the CFTR mutation is so common in select ethnic groups. Geneticists have determined that the important F508del mutation of the CFTR gene has been present in the human gene pool for over 50,000 years. As the condition has historically been lethal, it is widely assumed that the carrier state (a single CFTR mutation) must have afforded a survival advantage to certain populations. One clue is that ethnic groups with the highest prevalence of the CFTR mutation are indigenous to cooler climates, such as Ireland, parts of Scandinavia and other European regions. It is known that carriers of CF are predisposed to greater salt loss in their sweat than individuals without the gene. In these climates, salt loss in hot weather would be less relevant, compared to regions of Africa and Asia where the CFTR mutation is much more rare.

Proposed diseases that the CF carrier state may protect against include diarrhea from cholera or lactose intolerance, typhoid fever, high blood pressure and tuberculosis. While these theories have not yet been confirmed in humans, it seems likely that one (or more) of these mechanisms is responsible for keeping the CFTR mutation in the gene pool.

 

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