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Cystic fibrosis (CF) is the most common profoundly life-shortening inherited disease in North America. In 1938, Dr. Dorothy Andersen first described the complex of respiratory and digestive signs and symptoms that make up this syndrome,1 but references to a childhood disorder characterized by salty sweat and early death date back to at least the Middle Ages. The cellular and molecular bases for the disorder have recently been elucidated.2,3

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Epidemiology

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Cystic fibrosis (CF) is inherited as an autosomal recessive disorder. It is most common in those of northern European descent, with an incidence of approximately 1 in every 3200 live births. It is seen in about 1 in every 17,000 births in African Americans and is much less common in Asian populations. It has been found in virtually every ethnic and racial group. Approximately 4% of whites are heterozygous for CF (ie, carry one CF allele); heterozygotes have no evidence of clinical disease.

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Pathophysiology and Genetics

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CF affects virtually every organ system with epithelial surfaces—most importantly, the lungs, pancreas, intestinal mucus glands, liver, the reproductive tracts, and sweat glands. A common pathogenetic mechanism in major target systems is abnormal ion transport across epithelial surfaces. Impermeable chloride channels and overactive sodium pumps of these epithelial cells lead to biochemical and bioelectric abnormalities within organ lumina, leading in turn to viscid intralumenal secretions in the affected organs. These abnormally viscous secretions cause the blockage of ducts and air passages.

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The most common mutation in the CF gene is a three-base-pair deletion that leads to the loss of a single phenylalanine at position 508 of the protein product (“ΔF508”).4 The ΔF508 mutation accounts for 70% to 80% of CF chromosomes; about 50% of CF patients in North America are homozygous for this mutation. More than 1500 other mutations at the CF locus have been discovered, but these account for only a small percentage of CF cases. In a few ethnic groups, a small number of mutations account for a large proportion of CF cases (Table 514-1). Prenatal testing and carrier testing can be accomplished in virtually every family desiring this information.

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Table 514-1. Characteristics of Various CFTR Mutations 

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