Cystic Fibrosis | Symptoms and Causes

What are the symptoms of cystic fibrosis?

The symptoms of cystic fibrosis (CF) differ for each child, and some children may not show signs of CF until later in life. Infants born with CF usually show symptoms within the first year. Your infant may be tested for CF if he has the following symptoms:
  • diarrhea that does not go away
  • foul-smelling stools
  • greasy stools
  • frequent episodes of wheezing
  • frequent episodes of pneumonia
  • persistent cough
  • skin tastes salty
  • poor growth
  • chronic sinus infection

CF respiratory-system symptoms

Symptoms related to the respiratory system include:

  • chronic cough
  • coughing up blood
  • collapsed lung
  • clubbing (rounding and enlargement of the fingers and toes)
  • heart enlargement
  • nasal polyps (fleshy growths in the nose)
  • sinusitis (inflamed nasal sinuses)

Normally, mucus is thin and can be easily cleared by the airways. With CF, mucus becomes thickened, sticky and gradually blocks the airways. Eventually, cysts may develop due to this blockage. This can result in lung infections. These are quite common in children with CF, because bacteria that are normally cleared by the airways remain in the thickened mucus. Many of these infections are chronic and commonly caused by either the pseudomonas aeruginosa or staphylococcus (staph) bacteria.

About 10 to 20 percent of children with CF have nasal polyps­ — small protrusions of tissue from the lining of the nose — that need to be surgically removed.
Children with CF also have a high rate of sinus infections.

CF digestive-system symptoms

Symptoms related to the digestive system include:

  • frequent, bulky, greasy stools
  • rectal prolapse (a condition in which part of the lower intestinal tract comes out of the anus)
  • fat in the stools
  • stomach pain
  • bloody diarrhea
  • poor growth
  • gallstones

The gene that has the CF mutation — the CFTR gene — controls the flow of water and certain salts in and out of the body's cells. The mutation means that mucus throughout your child’s body becomes thickened. The pancreas secretes substances that help digestion. In around 90 percent of children with CF, these substances become thick, and cause ducts (passageways between organs) to become blocked, resulting in fewer enzymes.

With fewer digestive enzymes, a child will have difficulty absorbing the nutrients the body needs, especially:

  • fats
  • some proteins
  • fat-soluble vitamins such as A, D, E and K

What other risks are associated with CF?

In addition to affecting the respiratory and digestive systems, cystic fibrosis can also lead to diabetes. This is because problems with the pancreas may become so severe that some of its cells are destroyed, leading to glucose intolerance and insulin-dependent diabetes.

About 35 percent of CF patients develop this type of diabetes in their 20s, and more than 40 percent develop the disease after age 30.

A small number of patients may also develop liver disease. Signs of liver disease include:

  • enlarged liver
  • swollen abdomen
  • yellowish skin
  • vomiting of blood

What causes cystic fibrosis?

Cystic fibrosis is a genetic disease. Two things are true of all genetic diseases: their root cause is located on the cellular level and they are inherited. Because of this, we can look at what causes cystic fibrosis in two different ways — how it occurs on the cellular level and how a child comes to inherit the disease.

On the cellular level

As the name implies, a “genetic disease” is caused by something in the body’s genes. Genes are found on chromosomes — structures in the cells of our bodies that usually come in pairs.

One pair of chromosomes includes a gene called the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and mutations or errors in this gene are what cause CF. This gene is large and complex, and more than 1000 different CF-related mutations have been identified.

Inheriting CF

If a baby is born with CF, it means two CF genes were inherited, one from the mother and one from the father.

A person with only one CF gene is healthy and said to be a "carrier" of the disease. If both parents are carriers of the CF gene (they each have one copy of the defective gene, but do not have the disease themselves), their child has:

  • a 25 percent chance of inheriting both defective copies and having CF
  • a 50 percent chance of inheriting one defective copy and being a carrier
  • a 25 percent chance of not having CF and not carrying the gene

This type of inheritance is called "autosomal recessive." Autosomal means that the gene is on one of the pairs of chromosomes that do not determine gender, so that the disease equally affects males and females. Recessive means that two copies of the gene, one inherited from each parent, are necessary to have the condition.