Cystic fibrosis (CF), which is transmitted as an autosomal recessive trait, is the most common lethal genetic disease in the United States. Median survival age for patients followed up at CF centers in the US is now 21 years. While the disease is diagnosed in most patients before the age of 5 years, in 10% of cases the diagnosis is not confirmed until after age 12. We report an unusual family in which the diagnosis of CF was first established in three siblings at the ages of 36, 40, and 44 years. We describe the clinical features of the patients, as well as issues relating to the diagnosis of CF in adults. This unusual pedigree supports the concept of genetic heterogeneity in CF.
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