Cystic Fibrosis

Cystic fibrosis (CF) is an inherited disease of mucus and sweat glands. It affects mostly lungs, pancreas, liver, intestines, sinuses, and sex organs.

Normally, mucus is watery. It keeps the linings of certain organs moist and prevents them from drying out or getting infected. But in CF, an abnormal gene causes mucus to become thick and sticky. The mucus builds up in lungs and blocks the airways. This makes it easy for bacteria to grow and leads to repeated serious lung infections. Over time, these infections can cause serious damage to lungs.

The thick, sticky mucus can also block tubes, or ducts, in pancreas. As a result, digestive enzymes that are produced by pancreas cannot reach small intestine. These enzymes help break down the food. Without them, intestines cannot absorb fats and proteins fully, resulting in chronic malnutrition.

Respiratory failure is the most common cause of death in people with CF. Until the 1980s, most deaths from CF occurred in children and teenagers. Today, with improved treatments, people with CF live, on average, to be more than 35 years old. 

Symptoms

Most of the symptoms of cystic fibrosis (CF) are caused by the thick, sticky mucus. The most common symptoms include:

• Frequent coughing that brings up thick sputum, or phlegm (flem).
• Frequent bouts of bronchitis and pneumonia. They can lead to inflammation and permanent lung damage.
• Very salty sweat.
• Dehydration.
• Infertility (mostly in men).
• Ongoing diarrhea or bulky, foul-smelling, and greasy stools.
• Huge appetite but poor weight gain and growth because of chronic malnutrition.
• Stomach pain and discomfort caused by too much gas in intestines.

CF can also lead to other medical problems, including:

• Sinusitis. The sinuses are air-filled spaces behind your eyes, nose, and forehead. They produce mucus and help keep the lining of your nose moist. When the sinuses become swollen, they get blocked with mucus and can become infected. Most people with CF develop sinusitis.
• Bronchiectasis. Bronchiectasis is a lung disease in which the bronchial tubes, or large airways in your lungs, become stretched out and flabby over time and form pockets where mucus collects. The mucus provides a breeding ground for bacteria. This leads to repeated lung infections. Each infection does more damage to the bronchial tubes. If not treated, bronchiectasis can lead to serious illness, including respiratory failure.
• Pancreatitis. It is inflammation in the pancreas that causes pain.
• Episodes of intestinal blockage, especially in newborns.
• Nasal polyps, or growths in the nose, that may require surgery.
• Clubbing. It is the widening and rounding of the tips of the fingers and toes. It develops because your lungs are not moving enough oxygen into your blood stream.
• Collapsed lung. This is also called pneumothorax.
• Rectal prolapse. Frequent coughing or problems passing stools may cause rectal tissue from inside you to move out of your rectum.
• Liver disease due to inflammation or blocked bile ducts.

The symptoms and severity of CF vary from person to person. Some people with CF have serious lung and digestive problems. Other people have more mild disease that doesn't show up until they are adolescents or young adults.

Diagnosis

First, doctors will obtain a detailed medical and family history and perform a thorough physical examination. Then, they may order some tests to ensure an accurate diagnosis.

The sweat test is the most useful test for diagnosing cystic fibrosis (CF). It measures the amount of salt in your sweat. For this test, doctors rub a small amount of a chemical called pilocarpine  on your arm or leg. They then attach an electrode to this spot. The electrode provides a mild electric current that produces sweat. This may cause tingling or a feeling of warmth. They then cover the area with a gauze pad or filter paper and wrap in plastic. After 30 to 40 minutes, they remove the plastic so the sweat that collected on the pad or paper can be analyzed. The test is usually done twice. High salt levels mean CF.

Your doctor may also do the following tests to understand more about your condition and how to treat it:

• Blood tests to look for an abnormal CF gene or other things that indicate CF.
• Chest x ray. A chest x ray takes a picture of your lungs. It can show scarring from inflammation in your lungs.
• Sinus x ray. This test may show signs of sinusitis.
• Lung function tests can measure:
  • How much air your lungs can hold
  • How quickly you can breathe air out of your lungs
  • How well your lungs add oxygen to and remove carbon dioxide from your blood
• Sputum (phlegm) cultures. Doctors take a sample of your sputum to see what bacteria are growing in it.

If you are pregnant, prenatal genetic tests can find out if your baby has CF:

• In amniocentesis, your doctor inserts a hollow needle through your abdominal wall into your uterus to obtain cells from the fluid (amniotic fluid) around the baby. The fluid is then tested to see if both of the baby's CFTR genes are normal.
• In a chorionic villus biopsy, your doctor uses ultrasound to guide a thin tube through your vagina and cervix into your uterus and remove a tiny piece of the placenta to biopsy. The cells of the placenta are then tested to see if the baby has CF.

Causes

Cystic fibrosis (CF) is caused by a defect in a gene called the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This gene makes a protein that controls the movement of salt and water in and out of the cells in your body. In people with CF, the gene does not work effectively. This causes the thick, sticky mucus and very salty sweat that are the main features of CF.

Each of us inherits two CFTR genes, one from each parent.

• Children who inherit an abnormal CFTR gene from each parent will have CF.
• Children who inherit an abnormal CFTR gene from one parent and a normal CFTR gene from the other parent will not have CF. They will be CF carriers.

CF carriers:

• Usually have no symptoms of CF
• Live normal lives
• Can pass the abnormal CFTR gene on to their children

When two CF carriers have a baby, the baby has a:

• One in four chance of inheriting two abnormal CFTR genes and having CF.
• One in four chance of inheriting two normal CFTR genes and not having CF or being a carrier.
• Two in four chance of inheriting one normal CFTR gene and one abnormal CFTR gene. The baby will not have CF but will be a CF carrier like its parents.

Reference:

National Heart, Lung, and Blood Institute, USA.