We have analysed 972 unrelated Spanish cystic fibrosis patients for 70 known mutations. Analysis was performed on exons 1, 2, 3, 4, 5, 6a, 6b, 7, 10, 11, 12, 13, 14a, 14b, 15, 16, 17b, 18, 19, 20 and 21 of the cystic fibrosis transmembrane regulator gene using single strand conformation polymorphism analysis and denaturing gradient gel electrophoresis. The major mutation ΔF508 accounts for 50.6% of CF chromosomes, whereas another 42 mutations account for 27.6% of CF chromosomes, with 21.8% of Spanish CF chromosomes remaining uncharacterised. At present, we have identified 36 mutations that have frequency of less than 1% and that are spread over 15 different exons. This indicates that, in the Spanish population, with the exception of ΔF508 (50.6%) and G542X (8%), the mutations are not concentrated in a few exons of the gene nor are there any predominating mutations. This high degree of genetic heterogeneity is mainly a result of the different ethnic groups that have populated Spain and of the maintenance of separated population sets (Basques, Arab-Andalusian, Mediterranean, Canarian and Gallician). The high proportion of CF chromosomes still unidentified (21.8%) together with association analysis with intragenic markers suggest that at least 100 different mutations causing CF are present in our population.
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