MUTATIONS IN XANTHENE DEHYDROGENASE (XDH) ASSOCIATED WITH INHERITED SUSCEPTIBILITY TO BARRETT'S NEOPLASIA

Background: Barrett’s Esophagus (BE) develops after reflux-mediated injury to distal esophagus and is only known precursor of esophageal adenocarcinoma (EAC), a highly deadly and increasingly prevalent cancer. Inadequate understanding of the genetic determinants and causative mechanisms of BE / EAC limits the development of effective prevention and treatment strategies. We have previously shown that BE and EAC aggregate in a proportion of families, and that a family history is present in nearly 10% of patients with BE or EAC. Aim: To understand familial/inherited predisposition to BE / EAC, and identify the genetic determinants and causative mechanisms driving Barrett’s neoplasia. Methods: We performed exome sequencing of affected relatives from select FBE families followed by validation with sanger sequencing. Results: We discovered inherited deleterious germline mutations in xanthene dehydrogenase (XDH), a gene fundamental to cellular homeostasis, segregates with BE and EAC in 6% of FBE families and genome-wide association studies and our own familial linkage studies have indeed suggested Chromosome 2, which contains XDH, to harbor susceptibility alleles strongly associated with BE/EAC risk and identified 15 heterozygous rare/private germline variants in 18 of 301 FBE families that we accrued. The significance of the observed rare/private XDH variants was calculated using SORVA package. This weighted scheme is utilized to determine the p-value from a binomial cumulative distribution function. Overall, considering a list of 4 candidate genes being tested, the p-value that the variants identified in XDH would be by chance alone was 0.011. Notably, 10 of the 15 variants we identified in XDH were discovered in families or individuals who had BE with high-grade dysplasia or EAC, suggesting that genetic defects in XDH may underlie risk of more aggressive/advanced disease phenotypes. In addition to inherited defects, analysis of TCGA dataset showed XDH to harbor somatic mutations, in up to 4% of EACs. Additionally, our findings from qPCR analysis, showed significant downregulation of XDH in BE dysplasia and EAC cell lines, compared to BE-metaplasia and esophageal SQ cells (***P<0.0005). Further assessment of molecular dynamics by 3D organotypic culture and subsequent RNAScope XDH ISH assay, showed that XDH to be predominantly expressed in the suprabasal/superficial layers, as compared to basal cells, of the esophageal mucosa. Intriguingly, our functional studies on XDH germline variants showed >2-fold higher ROS activity in stably expressed EPC2 cells, upon exposure to acidic bile compared to WT. Conclusion: Taken together, loss/deficiency of XDH likely supports the development of Barrett’s neoplasia in both inherited and sporadic cases. Further molecular and phenotypic studies of this germline variant XDH will determine its association with BE/EAC risk