Cystic fibrosis: symptoms and causes

Cystic fibrosis (or cystic fibrosis) is a chronic, degenerative and fatal disease of the endocrine glands that produce mucus and sweat, for example:

  • sweat or salivary glands,
  • bronchial mucous glands,
  • Pancreas
  • Gall bladder.

The secretions will:

  • sticky
  • viscous.

As a result, the secretions accumulate and cause blockages in some organs, especially in:

  • Bronchia
  • Intestine
  • Pancreas, the production of digestive enzymes is impaired.

In addition, the sweat becomes more salty.
This disease adversely affects many bodily functions, which include:

  • Respiration
  • Digestion
  • Reproduction


Causes of cystic fibrosis

Cystic fibrosis is a genetic or hereditary disease.
Cystic fibrosis is caused by a gene mutation.
This genetic material encodes the CFTR protein: “regulator of transmembrane conductivity in cystic fibrosis”.
This protein is important for regulating the exchange of water and mineral salts within cells.
The CFTR protein is a channel on the outer cell wall and enables the transport of chlorine ions.
The consequences and symptoms depend on the location of the gene mutation.
The mutation can cause 5 types of functional damage:

  1. Reduction of protein synthesis
  2. Maturation defect
  3. Abnormal activation
  4. Change in ionic conductivity
  5. Regulatory errors

Symptoms vary greatly among patients with cystic fibrosis, depending on the type of gene mutation:

  • Protein CFTR is missing: typical cystic fibrosis.
  • Presence of a functioning CFTR percentage: attenuated symptoms. If at least 8% of messenger RNA is functioning, the patient has no pulmonary disorders.
  • Mutations that alter but do not block the functionality of the protein do not show typical symptoms.
  • Mutations that lead to changes in ion channel permeability (CFTR) cause milder symptoms.

Effect of cystic fibrosis on mucus

  • Exogenous glands produce mucus and release it into the organ epithelium (bronchi, pancreas).
  • The amount of water absorbed by the mucus depends on the concentration of mineral salts contained, this mechanism is called osmosis.
  • Water spontaneously diffuses from the solution with a lower salt concentration to the solution with a higher concentration.
  • The cells transport sodium and chlorine into the mucus. In this way, the water spontaneously distributes from the interstitial fluid (between the cells) into the mucus.
  • In patients with cystic fibrosis, the channel for chlorine transport is absent or does not work. The water does not shift and the mucus is not liquefied.

The result is dry mucus.

Inheritance of cystic fibrosis

Inheritance is autosomal recessive, so two defective genes are needed to develop the disease.

A person is a healthy carrier if he only carries a defective gene for cystic fibrosis.
The healthy carrier:

  • does not fall ill,
  • lives without symptoms.

However, if two healthy carriers of the defective gene have a child, there are:

  • 25% probability that the child does not inherit cystic fibrosis, lives symptom-free and does not become a carrier of the gene.
  • 50% probability that only one copy of the defective gene will be inherited. In this case, the baby does not get sick, but becomes a healthy carrier of the gene.
  • 25% chance that the child inherits both copies of the defective gene from the parents and suffers from cystic fibrosis.

Effect of cystic fibrosis on the organs

Lungs and respiratory tract

In cystic fibrosis, the following applies to the lungs:

  • They lose the ability to maintain a sterile surface.
  • They are gradually damaged by bacterial infections.

There are various hypotheses about the cause of predisposition to pneumonia and lung damage.

The hypothesis of excess salt

This hypothesis, proposed by Jeffrey Smith, Michael Welsh and colleagues at the University of Iowa, highlights the function of the CFTR gene as an anion channel.
According to this hypothesis, the liquid on the surface of normal respiratory tract has a low salt content (less than half of the plasma) because more salt is absorbed than water.

In patients with cystic fibrosis, the missing or defective CFTR protein causes a decrease in salt absorption. Thus, the salt content in the surface fluid of the respiratory tract is equal to that of the plasma.
This interferes with the action of natural antibiotics:

  • Lysozyme
  • Defensin

This hypothesis is based on laboratory experiments that have shown bacterial proliferation only in cultures of the cells of patients with cystic fibrosis.
The conclusion is that the excess salt in the patients’ airways makes the antibiotics ineffective.

Hypothesis of volume reduction

After studies conducted using various methods, Richard Boucher and colleagues at the University of North Carolina have come across a completely different result.
Their hypothesis is based on the ability of the CFTR protein to inhibit the activity of the epithelial sodium channel (ENaC). Thus, there is an increase in the transport of positive sodium ions (Na+).
The consequence is an increase in the absorption of chlorine and water from the mucus, which causes:


The intestine produces a smaller amount of secretions than normal, so there is a greater likelihood of developing a blockage due to:

  • dry and dehydrated stools,
  • too slow transport of the stool.

About 10% of children with cystic fibrosis develop meconium ileus, i.e. an intestinal obstruction, due to too tough and sticky stools.
This occurs at the level of the ileocecal valve, i.e. between the small intestine and the large intestine.
In adults, the loss of the pancreatic enzyme causes steatorrhea (fatty stool), which can compensate for the tendency to blockage of the intestine.


In 90% of people with cystic fibrosis, the pancreas is increasingly destroyed and replaced by fibrotic and cystic tissue.
The destruction of the pancreas is caused by the reduction of secretions in the pancreatic canal.

Normally, the glandular cells in the pancreas release digestive enzymes that mix with the sodium bicarbonate-enriched fluid produced in the cells of the channel.
This “juice” enters the duodenum, where it is used for fat digestion.
Pancreatic cell secretions may be normal, but fluid secretion in the secretory channels is significantly reduced.
The result is:

  • closure of the channels,
  • accumulation of mucus,
  • Reduction of secretions.

The pancreatic cells are sensitive to the increase in pressure caused by the closure of the ducts, and fibrosis occurs.

Over time, the disease can also damage the part of the pancreas that produces insulin, which allows the patient to develop diabetes.

Male genitalia

Consequences in the area of the vas deferens in men are:

  • Shutter
  • Degeneration

The human epididymis and seminal canals are thought to be the organs most sensitive to the destructive effects of cystic fibrosis.
In fact, men with very mild genetic mutations may lack vas deferens on both sides from birth, but there is no other feature of the disease.
Oppenheimer (University of Chicago Hospitals and Clinics) and Esterly have found that in boys, the absence of vas deferens is the result of occlusion.

Female genitalia

Cystic fibrosis can cause some effects that lead to female infertility, including:

Gall bladder

Less common symptoms include:

  • focal biliary cirrhosis,
  • a particularly small gallbladder.

Symptoms of cystic fibrosis

Symptoms can vary over time and from person to person.
Some newborns and infants with this condition may have serious problems associated with:

  • Lung
  • Digestion.

Others may develop serious symptoms as they grow up.
Most people with this condition have severe breathing disorders and respiratory insufficiency, which become the cause of death.

The most common symptoms of cystic fibrosis are:

Respiratory symptoms

  • Common lung infections such as pneumonia and bronchitis
  • Chronic viscous cough with catarrh or bloody tinged mucus
  • Noisy or wheezing breath
  • Frequent attacks of sinusitis
  • Some may develop a more severe condition, such as pneumothorax (lung collapse) or bronchiectasis (narrowing of the bronchi)
  • Some people develop nasal polyps that congest the nose and need to be surgically removed

Symptoms on the digestive system

Consequence for the sexual apparatus

  • Narrowing or absence of vas deferens (vas deferens that allow sperm to be transported from the testicles). This defect leads to male infertility (azoospermia or lack of spermatozoa in 98% of men with cystic fibrosis).
  • Women may have difficulty conceiving due to blockage of the cervix by viscous mucus.
  • The inner lining of the uterus is bound by the CFTR protein, which can alter the secretion and thus lead to female infertility.

General signs and symptoms

  • Massive salt excretion in sweat, leading to dehydration
  • Accelerated heartbeat (tachycardia)
  • Fatigue, weakness
  • Hypotension
  • Risk of heat stroke
  • Osteoporosis (decreased bone density)
  • Digital acropachia or drum flail fingers, which means that the end limbs of fingers and toes appear wider and more rounded.

In more severe cases, the affected person may also develop:

  1. dysfunction of the liver due to inflammation or blockage of the bile ducts that occur because the bile is too thick,
  2. Gall stones
  3. kidney stones,
  4. diabetes,
  5. pancreatitis (inflammation of the pancreas),
  6. Rectal prolapse (part of the rectum protrudes from the anus).


In some cases, the disease can be detected a few days after birth because the infants:

  • develop a salty taste on the skin due to excessive sweating,
  • have no bowel movements due to intestinal occlusion, also called meconium ileus.

Growth retardation may also occur due to poor food intake.
In most cases, the disease manifests itself in the first years of life, as a rule, the children show only mild symptoms.

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