Cystic Fibrosis

Updated October 3, 2019

This article was scientifically reviewed by Aishwarya Arjunan

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A list of references is also included at the bottom of this article.

Cystic fibrosis, CF, is a genetic condition that causes a build-up of thick, sticky mucus that can be harmful and damage many of the body’s organs

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Disclaimer: Before You Read

It is important to know that your genes are not your destiny. There are various environmental and genetic factors working together to shape you. No matter your genetic makeup, maintain ideal blood pressure and glucose levels, avoid harmful alcohol intake, exercise regularly, get regular sleep. And for goodness sake, don't smoke.

Genetics is a quickly changing topic. Read More...

CF is a chronic condition that worsens over time but thanks to improved treatments, the average life expectancy for an individual with CF is 40 years of age.

Early identification and treatment can help improve the quality of life for individuals with CF.

What Is Cystic Fibrosis?

Cystic fibrosis is a genetic condition that results in the production of thick, sticky mucus, mainly in the lung and digestive system.

While some amount of mucus is necessary to line various organs in the body for protection and lubrication, individuals with cystic fibrosis produce mucus that is very sticky and thick which can clog and obstruct organs throughout the body 1 2.

Cystic fibrosis is caused by mutations in the CFTR gene which is responsible for creating a channel that helps transport chloride ions in and out of cells 3.

Chloride is a vital component of sodium chloride (also known as salt, NaCl) that is found in sweat.

The movement of chloride in the cells helps control the movement of water in tissues which is needed to create thin, free flowing mucus 4.

Mutations in CFTR disrupt this process resulting in the thick and sticky mucus that is characteristic of cystic fibrosis.

Over 1,700 disease causing mutations have been identified in the CFTR gene 5. These mutations can be divided into classic and non-classic mutations.

Individuals with two classic mutations are at risk for a more severe presentation of the condition that includes issues with the pancreas.

Individuals with one classic and one non-classic mutation or even two non-classic mutations are likely to have a milder presentation of the condition and may not experience any issues with the pancreas.

Two of the primary systems that are affected in individuals with cystic fibrosis are the respiratory and digestive systems 6 7.

The reproductive system is also affected in most males and some females.

How Common is Cystic Fibrosis?

While cystic fibrosis can be seen in individuals of all ethnic backgrounds, males and females, it is the most common autosomal recessive genetic condition in the Northern European population.

In the United State, 1 in every 3,200 newborns is affected by cystic fibrosis and 1 in every 35 Americans may be a carrier of the condition 8 9.

Currently, there are approximately 30,000 people with cystic fibrosis in the United States 10.

The condition is also more common in the Ashkenazi Jewish population with 1 in every 29 individuals identified as a carrier of the condition.

It occurs with a lower frequency in other ethnic groups. Approximately 1 in 61 African Americans and 1 in 118 Asian Americans are observed to be a carrier of cystic fibrosis 11.

Typically, the condition is diagnosed shortly after birth as all newborns in the United States are screened for this condition along with a number of others within a few days of birth.

However, there are cases of some individuals with the milder form of the condition that may not get diagnosed until later in life.

What Are the Symptoms of Cystic Fibrosis?

The severity of the symptoms of cystic fibrosis varies from person to person. A hallmark feature of cystic fibrosis is salty sweat.

Individuals with cystic fibrosis have 2-5x the expected amount of salt or sodium chloride (NaCl) in their sweat.

The primary systems impacted in individuals with cystic fibrosis are the digestive and respiratory systems.

Respiratory System Symptoms 12 13:

Mucus can clog the airways which can lead to severe problems with breathing. Infections in the lungs can cause coughing, wheezing, and inflammation.

The recurrent infections and buildup of mucus can cause permanent lung damage.

Additional respiratory symptoms an individual can exhibit include:

  1. Wheezing
  2.  Shortness of breath (emphysema)
  3.  Stuffy nose or Inflamed nasal passages or nasal polyps
  4.  Frequent lung infections
  5.  Chronic cough that produces thick mucus (sputum)
  6.  Exercise Intolerance 

Digestive System Symptoms 14 15:

The pancreas is responsible for producing insulin, a hormone that helps control blood sugar levels, and other digestive enzymes.

When mucus builds up in the pancreas, it damages the ability to produce the necessary insulin and digestive enzymes the body needs.

This can lead to diarrhea, malnutrition, poor growth, and weight loss.

In some individuals, the impaired ability to produce insulin can result in a form of diabetes that is called cystic fibrosis-related diabetes (CFRD)

Additional digestive system symptoms include: 

  1. Pancreatic insufficiency
  2.  Pancreatitis (inflammation of the pancreas)
  3.  Inability to absorb nutrients
  4.  Intestinal blockages (meconium ileus)– especially in newborns
  5.  Greasy stools that smell foul
  6.  Chronic, severe constipation
  7.  Poor growth and weight gain despite a large appetite
  8. Gallstones
  9.  Liver disease
  10.  Rectal prolapse

Newborns who don’t pass their first stool, (meconium ileus), may be held in the hospital longer, at least until they do.

Meconium ileus is a characteristic finding in babies with cystic fibrosis.

Because CF causes mucus to become thicker, it increases the chance that the meconium will get stuck in the ileum.

Approximately 1 in 5 babies with cystic fibrosis is born with meconium ileus 16.

In approximately 20% of children with cystic fibrosis, chronic coughing or constipation can cause rectal prolapse 17.

Reproductive System Symptoms:

Most males (~95%) with cystic fibrosis have congenital bilateral absence of the vas deferens (CBAVD) 18.

CBAVD is caused when the vas deferens (tubes that carry sperm) are blocked by mucus and do not develop properly and leads to infertility.

While most females with cystic fibrosis have normal fertility, some may experience infertility due to abnormal cervical mucus.

Other Symptoms:

There are additional systems that are also impacted in individuals with cystic fibrosis.

Cystic fibrosis can also cause clubbing (widening and rounding of fingertips and toes) and osteoporosis (low bone density) 19.

Due to the increase of salt in the sweat of individuals, individuals are at risk for electrolyte imbalances and dehydration 20.

This can lead to other symptoms, such as:

  • Weakness
  •  Fatigue
  •  Low blood pressure
  •  Increased heart rate
  • Heat stroke

How is Cystic Fibrosis diagnosed?

In the United States, diagnosis of cystic fibrosis will generally come via newborn screening from a physician, generally a pediatrician or medical geneticist.

Every state’s newborn screening program for cystic fibrosis involves a blood test from the baby to check the levels of immunoreactive trypsinogen (IRT) which is made by the pancreas.

Elevated levels of IRT can trigger a positive newborn screen. Some states also include DNA screen along with the IRT test to look for a subset of mutations that are seen in individuals with cystic fibrosis.

Both of these tests are screens and are not diagnostic but these screens will help identify babies that are at increased risk of having cystic fibrosis and alert the pediatrician that additional diagnostic testing is necessary.

While most individuals with cystic fibrosis are diagnosed by the age of two, some individuals are diagnosed later in life.

This is because there is a variability in the severity of the condition and some may not be identified via newborn screening.

Sweat Test

The gold standard for diagnosing cystic fibrosis is a sweat test.

A sweat test measures the amount of chloride excreted in the sweat.

Sweat is collected by applying a chemical called pilocarpine alongside some electrical stimulation that helps induce sweat to a small area of the patient’s skin.

The collected sweat is then sent for analysis and the results of the sweat test are generally available within a few hours.

Sweat chloride levels are not expected to change as an individual gets older.

If an individual has cystic fibrosis, the sweat chloride test will show that the individual has a high chloride level.

Individuals will generally receive one of three results from a sweat chloride test. If a chloride level is:

  • Less than or equal to 29 mmol/L = CF is unlikely
  • Between 30 - 59 mmol/L = CF is possible and additional testing is needed
  • Greater than or equal to 60 mmol/L = CF is likely

The test is generally repeated if the chloride level falls in the 30-59 mmol/L range.

For individuals with possible or likely CF sweat chloride results, additional DNA testing is also performed to identify the specific genetic mutations an individual carriers.

Genetic Testing

Genetic testing for cystic fibrosis is completed by obtaining a blood sample from the patient and sending for CFTR analysis.

The test will look to see if there are any disease causing mutations in the CFTR gene.

The presence of two disease causing mutations will help confirm the diagnosis of cystic fibrosis.

There will be a subset of individuals who received sweat test results in the intermediate range and are identified to have no or one disease causing mutation.

These individuals are diagnosed as having CF-related metabolic syndrome or CRMS.

How is cystic fibrosis treated?

While there is no cure for cystic fibrosis, management involves treatment of the various symptoms that are present in an individual.

Each treatment plan is tailored to each individual and their symptoms. To a point, yes, the symptoms of the disorder are treatable.

The disorder will last a person’s lifetime, and eventually be responsible for their death.

There are different types of treatments including medicine, surgery, rehab and physical therapy.

The treatment plan a doctor prescribes is based on the severity of the symptoms and the person’s current quality of life.

As part of their daily routine, individuals with cystic fibrosis go through a combination of the therapies mentioned below 21 22:

  • Airway clearance- done with the aid of a caregiver, this helps loosen up the mucus that builds up in the lungs
  • Inhaled medicines – this type of medication helps with removing mucus from airways, making it easier for the patient to cough it up, improving their overall lung function.
  • Antibiotics – included in the inhaled medicines mentioned above, antibiotics are commonly prescribed for individuals who develop chronic infections due to recurrent mucus buildup.
  • Pancreatic enzyme supplements – these supplements aid in the absorption of vital nutrients the body needs to thrive.
  • CFTR modulator therapies - these medications are designed to correct the malformed protein that is produced by the CFTR gene. Three CFTR modulators have been developed so far (Kalydeco®, Orkambi®, and Symdeko®) and these modulators are only effective in individuals with particular mutations.

Rehabilitation and Physical Therapy

Pulmonary rehabilitation and physical therapy are extremely beneficial to a patient with cystic fibrosis.

Chest physical therapy involves the individual using gravity to drain mucus from the lungs.

It may also involve vest therapy or having a caregiver or partner clapping on the back of the chest to help move mucus out of the airways.

Pulmonary rehabilitation is used to address chronic breathing problems.

It addresses exercise training, nutritional counseling, breathing strategies, and techniques to conserve energy.

Surgery

In some instances, surgery may be necessary to address certain complications associated with the condition. These include:

  1. Nasal polyp removal
  2.  Bowel surgery
  3.  Feeding tube insertion
  4.  Endoscopy
  5.  Lung transplant 

What is the life expectancy of an individual with cystic fibrosis?

Currently there is no cure for the condition but the life expectancy of individuals with cystic fibrosis has increased drastically over the last two decades.

For individuals born with CF between 2013 and 2017, the life expectancy is predicted to be 44 years 23.

It is important to remember that individuals with cystic fibrosis experience a variety of different symptoms with some having a more severe disease progression than others so the prognosis can be quite different depending on the severity of the condition.

Improvements in treatment options have helped improve the quality of life for individuals with the condition but some individuals still face challenges such as frequent hospitalizations and time-consuming treatment plans.

How Is Cystic Fibrosis Inherited?

Cystic fibrosis is inherited in an autosomal recessive pattern. This means that people with cystic fibrosis have inherited two copies of the defective (or mutated) CF gene, one copy from each parent.

We have 46 chromosomes in each cell of our bodies. These chromosomes can be organized into 23 pairs.

One of each pair of chromosomes is inherited from each parent. Our genetic information, or our genes, is carried on the chromosomes.

Genes are instructions telling our bodies how to grow and develop.

While each person has two working copies of each gene, parents of children with cystic fibrosis will have one copy that has a mutation and one copy that is working without any problems.

Because they have one working copy of the gene, they do not have any signs or symptoms of CF.

This is called “autosomal recessive inheritance”. Parents who have one copy with a gene mutation are called “carriers”.

Credit: U.S. National Library of Medicine

CF occurs when an individual inherits two mutations in the CFTR gene.

When two carrier parents have a child who inherits both copies with a gene mutation, one from each parent, the child will have CF.

What are the chances that I will pass cystic fibrosis to my child?

  • If neither parent has a disease causing gene mutation; that is, neither parent is a carrier, then it is highly unlikely that cystic fibrosis will be passed down.
  • If only one parent has a mutation, is a carrier for CF, and the other parent has two normal working copies of the CFTR gene, the children of that couple will each have a 50 percent chance (1/2) of being an unaffected carrier of CF.
  • If both parents are carriers of CF, then there is a 1 in 4 or 25% chance in each pregnancy to have a child with CF. This also means that there is a 3 in 4 or 75% chance in each pregnancy to not have a child with CF.

Genetic testing for cystic fibrosis

While blood testing and looking for disease causing mutations in the CFTR gene can help establish a diagnosis of cystic fibrosis, a sweat chloride test is considered the gold standard for diagnosing cystic fibrosis.

Speak with your health care provider if you wish to learn more about genetic testing for cystic fibrosis.

A referral to a genetic counselor can be helpful to discuss the various testing options for you and your family.

Is prenatal testing available?

Genetics play a very critical part in whether a person develops the disorder, or even if they are a carrier who can pass it onto their children.

If parents want to know their risk of having a child with cystic fibrosis then they can consider getting carrier screening prior to or in the early stages of pregnancy.

Carrier screening will help identify whether an individual or couple are both carriers for cystic fibrosis and thus at risk of having a child with the condition.

If a couple is identified to both be carriers for cystic fibrosis, then prenatal diagnosis via chorionic villus sampling (CVS) or amniocentesis can help determine whether the fetus is affected.

If carrier screening is done prior to pregnancy and a couple is identified to both be carriers for cystic fibrosis then that couple can explore other options such as pre-implantation genetic testing with IVF, using an egg or sperm donor, or adoption.

Speaking with a genetic counselor can help determine if this testing is right for you.

Where can I go to get genetic testing?

There are a variety of options available for cystic fibrosis genetic testing

Genetic testing is generally ordered by a healthcare provider though there are now a few options available for you to get testing directly from a testing company.

When considering any form of genetic testing, it can be helpful to speak with your healthcare provider to learn about the benefits and limitations of testing and testing options.

It is always advised to complete diagnostic testing under the guidance of a healthcare provider. Testing completed through your doctor’s office will usually involve a blood sample.

Companies like 23andMe and Helix offer genetic testing that can help identify carriers.

It is important to compare these screens to testing that would be ordered by your provider to confirm whether they are as comprehensive.

Some direct to consumer tests may not offer as comprehensive of a screen compared to the one that you may get from your healthcare provider.

These direct to consumer tests typically involve a saliva or buccal sample.

You’ll be able to view your results online within 4-8 weeks.

It is important to note that results from at-home kits may not provide a complete answer.

DNA Testing for Cystic Fibrosis: Benefits and Limitations

Genetic testing can a mix of benefits and limitations. There is no possibility of physical harm or any biological risk in getting tested aside from the general risk of a blood draw if a blood draw is completed.

Although deciding on testing is entirely voluntary, it can prove to be a complex decision that may raise new health concerns or anxieties.

For this reason, it’s best to seek genetic counseling to help discuss the emotional and social aspects of genetic testing, as well as get an educated interpretation of the results.

With that in mind, here is a short list of the strengths and limitations:

Benefits of Genetic Testing:

  1. Relief from any uncertainty about whether or not CF is the appropriate diagnosis.
  2. In-depth understanding about the disease and how it impacts you and your health.
  3. You will be in a position to educate your family about the potential risk of passing down the condition or help diagnose other family members who may also have CF.
  4. Knowing you are a carrier can help you make future family-planning decisions.

Limitations of DNA Testing:

  1. Your new knowledge will not lead to a cure, but will help empower you to make decisions about your health and future
  2. You may not be able to get a conclusive answer after genetic testing which may then lead to a feeling of uncertainty about the diagnosis and family planning.

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Referenced Sources

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  14. Cystic Fibrosis Foundation. Retrieved online August 2019.
  15. Cystic fibrosis; CF.Online Mendelian Inheritance in Man, OMIM®. Johns Hopkins University, Baltimore, MD. MIM Number: 219700: 5/8/2019.
  16. Meconium Ileus. Seattle Children’s. Retrieved August 2019.
  17. Cystic Fibrosis Symptoms and Treatment. Children’s Hospital of Pittsburgh. Retrieved Online August 2019.
  18. Ong T, Marshall SG, Karczeski BA, et al. Cystic Fibrosis and Congenital Absence of the Vas Deferens. 2001 Mar 26 ,Updated 2017 Feb 2. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® Internet. Seattle (WA): University of Washington, Seattle; 1993-2019.
  19. Ong T, Marshall SG, Karczeski BA, et al. Cystic Fibrosis and Congenital Absence of the Vas Deferens. 2001 Mar 26 ,Updated 2017 Feb 2. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® Internet. Seattle (WA): University of Washington, Seattle; 1993-2019.
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