Evaluation of cystic fibrosis newborn screening program in Latvia

Newborn screening for cystic fibrosis (CFNBS) has revolutionized the diagnosis and early management of this common, inherited disease. CF NBS is performed in 22 European countries although using different strategies. CFNBS has introduced in Latvia in July of 2019 using a strategy that combines the detection of immunoreactive trypsinogen (IRT), sweat test, and DNA analysis for CFTR. The aim of the study is to evaluate CFNBS experience in Latvia. Data were gathered and evaluated for CFNBS from July 2019–December 2020. IRT was measured by fluorometric enzyme immunoassay, with a cutoff value of 70 µg/l. In case if the IRT is elevated for the first time (IRT1), the IRT level was detected for the second time (IRT2). All infants with elevated IRT2 were selected for a sweat test by Macroduct system and CFTR analysis – started with the detection of p.Phe508del and p.Ser18ArgfsX16 (CFTRdele2,3) variants, followed by Sanger sequencing and MLPA. 27057 neonates underwent CFNBS. Of these 490 (1.8 %) neonates had elevated IRT1, and 85 (0.3%) neonates had elevated IRT2. The sweat test was performed for 80 (94%) infants – there were no one borderline results, in four cases sweat test was positive (>60 mmol/l), 5 (6 %) of cases parents refused from test due to COVID-19 pandemic. Since CFNBS was introduced, CF was confirmed molecularly in four cases (all of them had positive sweat test) with the following genotypes: p.[Phe508del];[Phe508del]) in three cases, and one – p.[Ser168Leu];[Leu1335Pro]. In five cases the carrier status was confirmed (with normal range sweat test) with genotypes: p.[Phe508del];[=], p.[Arg553Ter];[=], and p.[Leu138dup];[=]. In all individuals who have elevated IRT twice and positive sweat test, the molecular analysis should be done starting with the detection of p.Phe508del and p.Ser18ArgfsX16 (CFTRdele2,3) variants following with CFTR gene sequencing and MLPA analysis.