Cystic fibrosis
Sometimes called mucoviscidosis, cystic fibrosis is a generalized dysfunction of the exocrine glands that affects multiple organ systems. Transmitted as an autosomal recessive trait, it’s the most common fatal genetic disease of white children.
Cystic fibrosis is a chronic disease; however, recent improvements in treatments have increased the average life
expectancy from age 16 to age 28 and older.
expectancy from age 16 to age 28 and older.
Incidence of cystic fibrosis is highest (1 in 3,000 live births) in Whites of northern European ancestry and lowest in Blacks (1 in 17,000 live births), Native Americans, and people of Asian ancestry. The disease occurs equally in both sexes.
Causes
Cystic fibrosis is an autosomal recessive disease resulting from mutations in a gene located on chromosome 7. The gene responsible for cystic fibrosis encodes a protein that involves chloride transport across epithelial membranes. The most common mutation in the cystic fibrosis gene involves a deletion resulting in absence of phenylalanine at the cystic fibrosis transmembrane regulator. There have been more than 800 mutations identified to date.
The immediate causes of symptoms are increased viscosity of bronchial, pancreatic, and other mucous gland secretions and consequent obstruction of glandular ducts. Cystic fibrosis accounts for almost all cases of pancreatic enzyme deficiency in children.
Signs and symptoms
The clinical effects of cystic fibrosis may become apparent soon after birth or may take years to develop. They include major aberrations in sweat gland, respiratory, and GI functions.
Sweat gland dysfunction
In cystic fibrosis, sweat gland dysfunction is the most consistent abnormality. Increased concentrations of sodium and chloride in the sweat lead to hyponatremia and hypochloremia and can eventually induce fatal shock and arrhythmias, especially in hot weather.
Respiratory symptoms
Such symptoms reflect obstructive changes in the lungs: wheezy respirations; a dry, nonproductive, paroxysmal cough; dyspnea; and tachypnea. These changes stem from thick, tenacious secretions in the bronchioles and alveoli and eventually lead to severe atelectasis and emphysema.
Children with cystic fibrosis display a barrel chest, cyanosis, and clubbing of the fingers and toes. They suffer recurring bronchitis and pneumonia and associated nasal polyps and sinusitis. Death typically results from pneumonia, emphysema, or atelectasis.
GI symptoms
The GI effects of cystic fibrosis occur mainly in the intestines, pancreas, and liver. One early symptom is meconium ileus; the newborn with cystic fibrosis doesn’t excrete meconium, a dark green mucilaginous material found in the intestine at birth. He develops symptoms of intestinal obstruction, such as abdominal distention, vomiting, constipation, dehydration, and electrolyte imbalance.
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