The spectrum of CFTR mutations in newly diagnosed cases of cystic fibrosis through newborn screening in the Republic of North Macedonia

Abstract

Objectives: The spectrum and frequencies of CFTR mutations varies considerably between populations and regions of the world. The Balkan region is known for greater heterogeneity, attributed to a long history of population migration in these countries from the Middle East and Europe. The aim of the study was to analyse the genotype in newly diagnosed cases of cystic fibrosis (CF) in the last 3 years, since newborn screening (NBS) for CF was introduced, including a 6 month pilot study. Methods: A 2-step IRT-IRT algorithm is performed, and then a sweat test (Macroduct sweat collection system followed by chloridometer chloride analysis) for confirmation/exclusion of the CF diagnosis when IRT values were both over the cut off: 70 ng/ml and 45 ng/ml, respectively. In cases of positive or borderline sweat tests, mutation analysis of CFTR gene is performed: snapshot reaction for 11 most common regional CFTR mutations or extended gene analysis: multiplex ligation-dependent probe amplification (MLPA), for detection of deletions/duplications, Sanger DNA sequencing or next generation sequencing. Results: During the study period, 24 cases were diagnosed with CF, 22 after positive NBS for CF and 2 cases with meconium ileus that were screening negative. Concerning their CFTR genotype, 11 cases were homozygote for F508del, 10 were compound heterozygotes for F508del and other CFTR mutation and 3 were without F508del mutation. The most common CFTR disease-causing mutation of F508del was found with an overall incidence of 66.7%. Other more frequent mutations were G542X (8.3%), N1303 K (6.2%) and 457TAT>G (4.2%). Six mutations were found in 1 CFTR allele each: G1349D, G126D, V456F, G551D, 621+1G->T and CFTRdupexon22. The last one is a newly discovered mutation with unknown consequences, found in a pancreatic-sufficient case. In only 1 patient did the second mutation remain to be proven by gene sequencing. Conclusion: Our region shows marked genetic heterogeneity for CF.