The DF508 screening in the Republic of Macedonia started in 1989 with the analysis of 19 CF patients, and showed one of the lowest frequencies (39.5%) of this mutation among all European countries [9]. In the next 5 years 64 additional patients suspected of CF were referred for analysis to our laboratory, but DF508 frequency reached only 47.9% [10], lower than that found in patients in the neighboring Bulgaria (58%), Greece (54%), Serbia (70%), and Albania (75%; E. Boletini, personal communication, 1996) [26-28]. 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 uncharacterized 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 in the past 12 years, and performed repeated analysis of the sweat test on patients in whom we could not detect any mutation. Using this approach, 107 patients were excluded from the CF registry because of the absence of chronic symptoms specific for CF and/or negative sweat tests. After this re-evaluation, 121 patients have been registered in the Republic of Macedonia, and the overall DF508 frequency is 62.4%, similar to that 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; thus, the molecular defect is known in 189 (78.0%) of the CF chromosomes. Only four of these mutations (G522X, N1303K, CFTRdele21kb and 621+1G®T) were found with a frequency of more than 1% (5.3, 2.2, 1.6 and 1.3%, respectively); four mutations were detected in two unrelated patients, while four novel mutations (711+3A®G, 1811+1G®C, V1337E and Y569C) were present only in isolated cases. Concerning the genotype of the patients, both mutations were characterized in 75 patients, in 38 patients only one mutation was found, while in eight patients both CF mutations remained unknown. The remaining uncharacterized 53 (22%) CF alleles are most likely large deletions, or may reside in regulatory regions of the CFTR gene that were not evaluated in this study [29,30].

Table 3. Prenatal diagnosis of cystic fibrosis performed in the Republic of Macedonia