In this paper updated and extended data on the frequency and distribution of cystic fibrosis (CF) mutations in a cohort of 121 patients from the Republic of Macedonia are presented. The molecular characterization of CF in the Republic of Macedonia was initiated in 1989. Since the beginning of the program for molecular characterization, a total of 228 unrelated patients suspected of carrying the disease were referred for genetic testing to the laboratory of the Research Center for Genetic Engineering and Biotechnology (RCGEB), Macedonian Academy of Sciences and Arts (MASA) at Skopje, Republic of Macedonia. The DNA methodology used for molecular characterization of CF mutations included polymerase chain reaction (PCR) amplification followed by dot-blot hybridization, restriction digestion, single-strand conformational polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE) and sequencing. The first screening performed in 1990 showed a very low frequency of the DF508 mutation (39.5%). In the next 5 years many additional CF families were studied; however, the DF508 frequency ( 47.9%) was still lower than that found in other populations. These data suggested the presence of a common, but at that time unknown, mutation that is responsible for the disease in Macedonian CF patients. Therefore, we implemented a rigorous, sensitive and extensive DNA analysis of unch-aracterized CF chromosomes, but failed to detect any mutation that would explain the observed differences. In 2001 we performed a careful re-examination of the clinical course of the disease in all 228 patients referred to our laboratory. Using this approach, 107 patients were excluded from the CF registry. After this re-evaluation, the overall DF508 frequency is 62.4%, similar to frequencies described in other Southeast European populations.

      During the course of this study, 12 other mutations, representing 15.6% of all CF alleles, were also identified. The molecular defect is now known in 78% (189/242) of the CF chromosomes.

      Thirty-one prenatal diagnoses were performed in 31 families at-risk for a child with CF.

      Key words: cystic fibrosis (CF), CF transmembrane regulator (CFTR), mutations, frequency