Evidence from Human and Zebrafish that GPC1 is a Biliary Atresia Susceptibility Gene

Background & Aims Biliary atresia (BA) is a progressive fibro-inflammatory disorder of infants involving the extra- and intra-hepatic biliary tree. Its etiology is unclear, but is believed to involve exposure of a genetically susceptible individual to certain environmental factors. Biliary atresia occurs exclusively in the neonatal liver, so variants of genes expressed during hepatobiliary development could affect susceptibility. Genome-wide association studies previously identified a potential region of interest at 2q37. We continued these studies to narrow the region and identify BA susceptibility genes. Methods We searched for copy number variants that were increased among patients with BA (n=61) compared to healthy individuals (controls; n=5,088). After identifying a candidate gene, we investigated expression patterns of orthologs in zebrafish liver, and the effects of reducing expression, with morpholino antisense oligonucleotides, on biliary development, gene expression, and signal transduction. Results We observed a statistically significant increase in deletions at 2q37.3 in patients with BA that resulted in deletion of 1 copy of GPC1, which encodes glypican 1—a heparan sulfate proteoglycan that regulates Hedgehog signaling and inflammation. Knockdown of gpc1 in zebrafish led to developmental biliary defects. Exposure of the gpc1 morphants to cyclopamine, a Hedgehog antagonist, partially rescued the gpc1-knockdown phenotype. Injection of zebrafish with recombinant Sonic Hedgehog led to biliary defects similar to those of the gpc1 morphants. Liver samples from patients with BA had reduced levels of apical GPC1 in cholangiocytes, compared with samples from controls. Conclusions Based on genetic analysis of patients with BA and zebrafish, GPC1 appears to be a BA susceptibility gene. These findings also support a role for Hedgehog signaling in the pathogenesis of BA.