Investigating the genetic profile of familial atypical cystic fibrosis patients (DeltaF508-CFTR) with neonatal biliary atresia.

Biliary atresia (BA) is a progressive inflammatory process of the biliary tree resulting in biliary obstruction. No single known genetic or environmental factor has been established to cause BA. Cystic fibrosis (CF) is a rare cause of neonatal cholestasis, and it has never been described in familial BA cases. Here, we investigate two siblings of first-degree consanguineous parents presenting with neonatal BA. Shortly after the Kasai operation, the proband developed severe respiratory symptoms attributable to a missed CF diagnosis. This was discovered after re-investigating the family history, which revealed a first-degree cousin with CF who did not manifest BA. Afterwards, we identified a pathogenic variant (DeltaF508) in CFTR in both BA-affected siblings along with their cousin. This intrigued us to study the molecular etiology behind the familial BA presentations, which exclusively contributed to BA-pathogenesis in BA-CF-affected siblings and not in their CF-only affected cousin. We applied a multistep approach to investigate the variant profile of both siblings' and their cousin's exomes. We curated the genes whose variants were shared by the BA-CF siblings but absent or heterozygous in their CF-only-affected cousin. Consequently, we identified three candidate genes (SNAPC4, UCK1, and ZHX2) besides CFTR. We propose that these genes act cumulatively or individually in inducing BA-pathogenesis-either by aggravating the biliary damage in the context of CF or increasing the susceptibility of BA as a separate CF-comorbidity. To our knowledge, this is the first report of DeltaF508 in CFTR with familial neonatal BA cases.