Introduction

The hybrid allele 1 of carboxyl-ester lipase (CEL-HYB1) created by the recombination of CEL and its pseudogene CELP has been linked to the development of chronic pancreatitis (CP) in German and French populations. [1] However, a Polish study failed to replicate a significant association with CP. [2] Moreover, recent observations suggested that polymorphic variants within CEL-HYB1 determine its effect on CP risk. Thus, the Thr488-Ile548 haplotype was designated as pathogenic while the Thr488-Thr548 haplotype was considered relatively benign. [3]

Aims & Methods

Our aim was to investigate the association of CEL-HYB1 and CP in a Hungarian cohort and re-assess the role of CEL-HYB1 haplotypes in European CP cohorts. The CEL-HYB1 allele was screened in 319 CP patients and 618 healthy controls from the Hungarian National Pancreas Registry by melting curve analysis and PCR. To investigate the CEL-HYB1 haplotypes, Sanger sequencing was used in Hungarian, and previously reported German, French and Polish CEL-HYB1 positive subjects. HEK 293T cells were transfected with CEL-HYB1 constructs containing the Thr488-Thr548 and Thr488-Ile548 haplotypes and expression of BiP mRNA was measured as a marker of endoplasmic reticulum (ER) stress.

Results

The CEL-HYB1 allele was significantly overrepresented in the Hungarian CP cohort (9/319, 2.82%) relative to controls (5/618, 0.81%) (P=0.0239, OR=3.56, 95% CI=1.18-10.71). Haplotype analysis revealed that all Hungarian (9 patients and 5 controls) and French (17 patients and 9 controls) CEL-HYB1 positive subjects carried the Thr488-Thr548 haplotype. Interestingly, 7/19 (37%) German and 2/6 (33%) Polish CP patients carried the Thr488-Ile548 haplotype, while the haplotype of German (19) and Polish (8) controls was exclusively Thr488-Thr548. BiP mRNA levels in cells expressing the Thr488-Thr548 or Thr488-Ile548 CEL-HYB1 haplotypes were significantly higher in comparison to cells transfected with empty vector (P<0.0001). Notably, cells expressing the Thr488-Ile548 haplotype had significantly higher levels of BiP transcripts than cells transfected with the Thr488-Thr548 CEL-HYB1 haplotype (P=0.006).

Conclusion

The CEL-HYB1 allele is a relatively strong risk factor for CP in Hungary. We observed ethnic differences in the CEL-HYB1 haplotype distribution among European cohorts. The higher CP risk associated with the Thr488-Ile548 haplotype might be explained by the stronger ER stress response it triggers in pancreatic acinar cells.

References

1. Fjeld K et al. A recombined allele of the lipase gene CEL and its pseudogene CELP confers susceptibility to chronic pancreatitis. Nat Genet 2015; 47: 518–522.
2. Oracz G et al. The hybrid allele 1 of carboxyl-ester lipase (CEL-HYB1) in Polish pediatric patients with chronic pancreatitis. Pancreatology 2019; 19: 531-534.
3. Brett MC et al. Single nucleotide polymorphisms in CEL‐HYB1 increase risk for chronic pancreatitis through proteotoxic misfolding. Hum Mutat 2020; 1–12.