RAPID CHARACTERIZATION OF THE VARIABLE-LENGTH POLYTHYMIDINE TRACT IN THE CYSTIC-FIBROSIS (CFTR) GENE - ASSOCIATION OF THE 5T ALLELE WITH SELECTED CFTR MUTATIONS AND ITS INCIDENCE IN ATYPICAL SINOPULMONARY DISEASE

The CFTR intron 8 variable length polythymidine tract. modulates the c ystic fibrosis (CF) phenotype associated with the mutation R117H. To e xplore whether other mutations reside on multiple intron 8 backgrounds with discernible impacts on phenotype, we developed an allele-specifi c PCR assay to characterize this locus. Our approach types samples rap idly without the use of radioisotopes, Polythymidine alleles were iden tified for mutations either associated with a wide range of clinical p henotypes (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, R55 3X, R334W, S945L and R75Q). R117H was detected in cis with each of thr ee alleles (5T, 7T, 9T) at the intron 8 locus. The navel R117H-9T asso ciation was detected in a 10-month old African-American male with bord erline-to-mildly elevated sweat chloride values (similar to 50-66 mEq/ L). All other mutations studied were associated with 7T except 3849+10 kb C>T, which was detected on both 7T and 9T backgrounds, but not 5T. Three individuals with a Delta F508/3849+10kb C>T genotype were 9T,9T and had pancreatic sufficiency and normal sweat chloride values, where as 15 others who carried 3849+10kb C>T on a 7T background had variable pancreatic function (sufficient, n = 12, insufficient, n = 3), and va riable sweat chloride values (normal, n = 12, elevated, n = 3). Surpri singly, 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 CE I n summary, the 5T allele was not found in cis with CF-causing mutation s besides R117H, but an elevated 5T allele frequency in variant CF pat ients suggests 5T may be associated with disease in some situations. ( C) 1997 Wiley-Liss, Inc.