Editor—Cystic fibrosis (CF) is one of the most common autosomal recessive disorders, with an incidence of one in every 2000 to 3000 white people. The disease is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene.1 Over 800CFTR mutations have been identified.2 Five mutations in Ashkenazi Jews,3 4 24 in whites,5 and 15 in African-Americans6 account for 97%, 90%, and 75% of CF chromosomes in the respective populations. In contrast, 90% of CF Spanish alleles were contributed by as many as 75 mutations, indicating a heterogeneous CF genotype in Spain.7 The overall mutation spectrum and the frequency of common mutations in a particular population depend on the ethnic background. For example, the frequency of the W1282X mutation is 1.2% in the white population, but it is as high as 60% in Ashkenazi Jews.8 That of ΔF508 is 70% in northern Europeans but it is less than 50% in Spanish and Hispanics.7 9 In order to provide accurate genetic counselling, it is necessary to determine the prevalent mutations in each ethnic group. A study of Hispanic CF patients from the south western United States showed that only 58% of Hispanic CF alleles were detected by screening 23 recurrent mutations.9 Thus, there is a need to identify the mutations accounting for the remaining Hispanic CF chromosomes. In addition, on identification of mutations genotype-phenotype correlation studies can be facilitated.

The clinical diagnosis of CF has been recently reviewed.10 Although the structure and function of ΔF508 and W1282X mutant CFTR have been studied, there is a shortage of genotype-phenotype correlation studies of rare mutations, particularly the ones that appear to be unique to Hispanic CF patients. This is partly because of the lack of an effective method for …