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INTRODUCTION AND HISTORICAL BACKGROUND
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Learning Objectives
The student will be able to describe the genetics, most common gene mutations, and protein abnormalities that characterize cystic fibrosis (CF).
The student will be able to define the competing hypotheses that have been proposed to cause the clinical manifestations of CF.
The student will be able to outline the approaches to identify CF patients through newborn screening, and describe the typical presenting signs and symptoms of CF lung and gastrointestinal disease.
The student will be able to identify the sequence of events that occurs in CF and the rationale for treatment interventions, including for non-pulmonary organs.
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Cystic fibrosis (CF) was first formally described in 1938 by the pathologist Dorothy Andersen, who recognized a number of patients with characteristic lesions of the pancreas and a clinical syndrome of failure to thrive, diarrhea, and recurrent respiratory infections. However, CF was recognized in European folklore hundreds of years earlier, and anticipated the sweat electrolyte abnormalities in CF. An anonymous medieval German source wrote, "Woe is the child who tastes salty from a kiss on the brow, for he is cursed, and soon must die." Shortly after Andersen's description, CF was recognized as an autosomal recessive disorder. By the mid-1950s, sweat electrolyte abnormalities were identified in CF and the technique to perform a sweat test was described that remains the gold standard to this day. Discovery of the CF gene in 1989 provided a critical advance in understanding the basic defect and pathophysiology in CF, and triggered a number of important advances in treating CF patients. As a direct result, the prognosis for patients with CF continues to improve (see below).
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Cystic fibrosis is now recognized as the most common lethal genetic disease in the Caucasian population, with an estimated 30,000 patients in the United States and 27,000 in Europe. CF is most common among Caucasians of northern European descent, with a disease prevalence of ~1 in 3,000 births, and the frequency of being a carrier of a defective CF gene is estimated as 1 in 29. The disease occurs less commonly in other ethnic groups, having approximate incidences of 1 in 4,000-10,000 Latin Americans, 1 in 15,000 African Americans, and 1 in 35,000 Asian Americans.
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ETIOLOGY AND GENETICS OF CYSTIC FIBROSIS
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CF is an autosomal recessive disorder caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The CFTR gene is located on the long arm of chromosome 7 at position 7q31. Over 2,500 distinct CFTR mutations have been identified, but deletion of phenylalanine at position 508 (ΔF508) of the CFTR protein is by far the most common. Between 65% and 75% of CF patients in the United States are homozygous or compound heterozygous for a ΔF508 mutation.
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The CFTR protein is expressed primarily on the apical membrane of epithelial cells, where ...