Risk of CFTR-related disorders and cystic fibrosis in an Italian cohort of CRMS/CFSPID subjects in preschool and school age.

The identification of cystic fibrosis screening-positive, inconclusive diagnosis (CFSPID) in infants is a controversial outcome of newborn screening for cystic fibrosis (CF). Today, despite improvements in the knowledge of CFSPID and the description of several cohorts, little data are available on cohorts with a follow-up period of more than 6 years. In this study, we report the outcomes of an Italian cohort of CFSPID individuals with CFSPID or formerly CFTR-related disorders (CFTR-RD) (CFSPID > CFTR-RD) or diagnosed with CF (CFSPID > CF). This was an observational and multicentre Italian study collecting clinical data on CFSPID born between the period January 1, 2011, and December 13, 2019. A total of 268 participants were included: 243 with persistent CFSPID, 7 with CFSPID > CFTR-RD, and 18 with CFSPID > CF. The trend of sweat chloride (SC) values, percentage of definitive diagnoses, lung function in school-aged children, and development of CF-related complications were evaluated. At the end of the observation period, almost 80% of the individuals with CFSPID did not have a conclusive diagnosis. A total of 29 children (10.8%) transitioned to a diagnosis of CF for pathological SC values (≥ 60 mmol/L) or multi-organ involvement, and 18 (6.7%) to CFTR-RD. Children who were followed up for > 6 years (median age, 7.5 years; range, 6.04-10.5) had normal lung function and were pancreatic sufficient, and the evolution in CF was only present in two cases. CONCLUSION: Most Italian preschool and school-aged children with CFSPID did not have a conclusive diagnosis, and progression to CF was unlikely in children > 6 years of age. An annual follow-up could be indicated to identify early evolution in clinical features consistent with a CFTR-RD. WHAT IS KNOWN: • Cystic Fibrosis newborn screening identifies also subjects with an inconclusive diagnosis (CFSPID). • Over time a variable percentage of CFSPIDs will be diagnosed as CF. • Little data is available on CFSPIDs with a follow-up period of more than six years. WHAT IS NEW: • 80% of Italian preschool and school-age CFSPIDs not have a conclusive diagnosis. • Italian preschool and school-age CFSPIDs have normal lung function and are pancreatic sufficient. • Annual follow-up after 6 years is recommended in CFSPID with abnormal LCI2.5 or with a CF-causing variant in trans with a VVCC.