| Abstract: | The CFTR intron 8 variable length polythymidine tract modulates the cystic fibrosis (CF) phenotype associated with the mutation R117H. To explore whether other mutations reside on multiple intron 8 backgrounds with discernible impacts on phenotype, we developed an allele-specific PCR assay to characterize this locus. Our approach types samples rapidly without the use of radioisotopes. Polythymidine alleles were identified for mutations either associated with a wide range of clinical phenotypes (R117H, R347P, G85E, D1152H, R334W, 2789+5 G>A, 3849+10kb C>T), and/or located at hypermutable CpG loci (R117H, 3849+10kb C>T, R553X, R334W, S945L and R75Q). R117H was detected in cis with each of three alleles (5T, 7T, 9T) at the intron 8 locus. The novel R117H-9T association was detected in a 10-month old African-American male with borderline-to-mildly elevated sweat chloride values (˜50–66 mEq/L). All other mutations studied were associated with 7T except 3849+10kb C>T, which was detected on both 7T and 9T backgrounds, but not 5T. Three individuals with a ΔF508/3849+10kb C>T genotype were 9T,9T and had pancreatic sufficiency and normal sweat chloride values, whereas 15 others who carried 3849+10kb C>T on a 7T background had variable pancreatic function (sufficient, n = 12, insufficient, n = 3), and variable sweat chloride values (normal, n = 12, elevated, n = 3). Surprisingly, when not associated with known CFTR mutations, 5T was detected with elevated frequency among individuals with sinopulmonary disease of ill-defined etiology, but with some characteristics of variant CF. In summary, the 5T allele was not found in cis with CF-causing mutations besides R117H, but an elevated 5T allele frequency in variant CF patients suggests 5T may be associated with disease in some situations. Hum Mutat 10:108–115, 1997. © 1997 Wiley-Liss, Inc. |
