Mild course of cystic fibrosis associated with heterozygosity for infrequent mutations in the first nucleotide-binding fold of CFTR.

The mild clinical course of a patient with cystic fibrosis is presented who inherited the two mutations Gly551----Asp and Arg553----Stop in the cystic fibrosis transmembrane conductance regulator gene. The missense mutation Arg553----Stop discovered in American Blacks is also present on cystic fibrosis chromosomes of Caucasian ancestry.