The discovery may mean that another gene, as yet unidentified, is to blame for these cases, or perhaps these patients really have another, unknown disease, despite the similarity of symptoms, the researchers suggest.
Loss of the function of a protein called CFTR was identified more than a decade ago as the cause of CF, a life-shortening disease characterized by frequent, severe lung infections. In less severe cases, known as "non-classic" CF, patients retain some working CFTR, but not at normal levels. Over the years, scientists have linked these conditions to more than 1,000 changes in the gene for CFTR.
"Our findings should lead to a discussion about what is, and is not, non-classic cystic fibrosis," says Garry Cutting, M.D., director of the DNA Diagnostic Lab at the McKusick-Nathans Institute of Genetic Medicine at Hopkins. "Hopefully, extensive clinical evaluation of patients without identifiable changes in the gene for CFTR will improve diagnosis and treatment of cystic fibrosis and cystic fibrosis-like conditions."
In the new study, of 74 patients diagnosed with non-classic CF and referred to the Cystic Fibrosis Foundation Genotyping Center at Hopkins, detailed genetic analysis showed that 29 had mutations in both copies of the CFTR gene, 15 had only a single mutation and 30 had no detectable changes in their CFTR genes. (One copy is inherited from each parent.) Cutting says other researchers now report the same observation.
"These patients were referred by physicians experienced with cystic fibrosis, and we expected to find a causative mutation in ea
Contact: Joanna Downer
Johns Hopkins Medical Institutions