National Newborn Screening for cystic fibrosis in the Republic of Ireland: genetic data from the first 6.5 years.

Cystic fibrosis (CF) is the most common life-limiting autosomal recessive disease in the Republic of Ireland (ROI), with a previously quoted incidence of 1 in 1353 and carrier rate of 1 in 19. The National Newborn Screening (NBS) for CF was incorporated in July 2011 in the ROI. A cut-off point of the top 1% Immunoreactive Trypsinogen (IRT) was taken as an indication for 38 CFTR variant panel to maximise identification of affected CF cases and to minimise detection of carriers. All neonates from July 2011 to Dec 2017 with an elevated IRT on NBS were tested with 38 CFTR mutation panel and included. Clinical and laboratory database were analysed. In the first 6.5 years a total of 5,053 newborns (1.16% of total births) were screened with 38 CFTR panel. 170 CF affected cases, 320 unaffected carriers, 32 CF Screening Positive Inconclusive Diagnosis (CFSPID) were identified. There was one missed diagnosis. The most common disease-causing variant was c.1521_1523delCTT (p.(Phe508del)) followed by c.1652G>A (p.(Gly551Asp)). 95 out of 170 (55%) affected newborns were homozygous for c.1521_1523delCTT (p.(Phe08del)) and 25 (15%) carried at least one copy of c.1652G>A (p.(Gly551Asp)). Hence, 70% of affected newborns were eligible for CFTR modulator treatment. The NBS programme has identified almost triple the number of affected newborn with c.1652G>A (p.(Gly551Asp)) than previously quoted figures and identified less than 50% of carriers than predicted. The revised incidence and carrier frequency of CF in the ROI is 1 in 2570 and 1 in 25, respectively.