Cystic fibrosis (CF) is an autosomal recessive disorder that is caused by over 850 different mutations in the CF gene. It is useful to group these mutations according to the defect that results in the CFTR mRNA or protein. New pharmacological treatments targeted towards specific mutations that are relatively common are being developed. Class I mutations do not produce CFTR protein because of a premature stop signal in the CFTR DNA. These null mutations can be corrected by certain aminoglycosides which cause the aberrant stop signal to be skipped. Mutations leading to a CFTR protein that attains an unstable structure shortly after translation in the endoplasmic reticulum form class II. Class II mutations can be restored to the protein trafficking pathway by manipulation of chaperone protein/CFTR interactions with chemical chaperones or drugs that affect gene regulation such as the butyrates. Production of a CFTR with reduced Cl transport on the basis of abnormal regulation of the chloride channel is the basis of class III. Genistein can overcome this block in regulation. Mutations that partially reduce chloride conductance through CFTR (class IV) can be stimulated with milrinone, which is a phosphodiesterase inhibitor. Finally, mutations that lead to a severe reduction in normal CFTR protein form class V. Increased levels of CFTR could be generated with the butyrates or supplemented with gene therapy. Although most of the reported mutations in CFTR are rare and unclassified, it may be possible to use genotype-phenotype correlations to determine the best approach.

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