Cystic Fibrosis
Cystic fibrosis is caused by a defect in the gene responsible for manufacturing cystic fibrosis transmembrane conductance regulator (CFTR), a protein that controls the flow of chloride ions into and out of certain cells. In healthy people, CFTR forms a channel in the plasma membrane through which chloride ions enter and leave the cells lining the lungs, pancreas, sweat glands, and small intestine. In people with cystic fibrosis, malfunctioning (or absent) CFTR prevents chloride from entering or leaving cells, resulting in production of a thick, sticky mucus that clogs ducts or tubes in these organs. In the lungs, this mucus blocks airways and impedes natural infection-fighting mechanisms, eventually turning the body’s immune system against its own lung tissue. Similar blockage prevents crucial digestive enzymes produced in the pancreas from reaching the intestines, impairing the ability to break down certain foods. In healthy people most of the chloride in sweat is reabsorbed, but in people with cystic fibrosis, sweat glands cannot take up chloride ions, enabling excessive amounts of salt to escape in the sweat.
Depending on the disease’s severity, symptoms may be apparent soon after birth, or they may escape detection for months or years. In nearly 20 percent of all cases, the first symptom is meconium ileus, intestinal blockage in newborns. In other babies, the first evidence of cystic fibrosis is bulky stool, poor weight gain, flabby muscle tone, or slow growth, all products of low levels of digestive enzymes in the intestines.
The earlier a diagnosis is made the better so that early treatment can slow the progression of lung damage caused by infection. Prenatal tests are available to determine if a baby will be born with cystic fibrosis. In newborns, blood tests indicating high levels of digestive enzymes suggest cystic fibrosis, but a certain diagnosis requires a sweat test to determine the amount of salt in the sweat. Sweat tests provide a valid diagnosis in babies over 24 hours old, and this test is also used to confirm diagnosis in older children and adults.
Cystic fibrosis remains incurable; existing treatments aim to relieve discomfort and delay the devastating and inevitable effects of the disease. Meconium ileus, the intestinal obstruction occurring in newborns, may require surgery. Patients with pancreatic blockage must take pancreatic enzymes with meals. Even with such enzymes, people with cystic fibrosis must consume adequate amounts of protein, vitamins, and higher-than-normal amounts of fat to ensure growth. Those with respiratory infections are treated with antibiotics, often in aerosol form. When inhaled, these medicated vapors fight infection and relieve constriction of the airways. Using a procedure called chest physical therapy or postural drainage, caregivers of people with cystic fibrosis repeatedly and vigorously pound on the patient’s back and chest to dislodge mucus obstructing the airways. Increasingly, cystic fibrosis patients with severe, irreparable lung damage turn to lung transplantation surgery (see Medical Transplantation).
Comments