Statistics from Altmetric.com
We read with great interest the recent publication by Németh et al.1 in which the authors demonstrate that a misfolding human cationic trypsinogen (serine protease 1, PRSS1) variant causes autosomal dominant hereditary chronic pancreatitis (CP) by inducing endoplasmic reticulum (ER) stress. Previously, the same mechanism was proposed for carboxypeptidase A1 (CPA1) gene variants strongly associated with early onset sporadic CP;2 however, the association of misfolding CPA1 variants with familial or hereditary CP has not been demonstrated so far.
Here, we report two Polish families with hereditary CP carrying a novel heterozygous c.844T>C (p.Ser282Pro) CPA1 variant. In Family 1, the index patient, her mother and uncle (half-brother of the mother) developed CP (figure 1). The age of diagnosis was 17 years for the index patient and 51 and 31 years (with earlier abdominal pain) for the mother and the uncle, respectively. In Family 2, three members were affected by CP (figure 1): the index patient, her mother and her father with ages of onset of 12, 32 and 34 years, respectively. In both families, the diagnosis of CP was confirmed by imaging methods. CP risk factors such as alcohol abuse, smoking, injury, anatomical defects, metabolic and bile duct disorders were excluded.
Each person gave informed consent for genetic testing. All exons of CPA1, PRSS1, SPINK1, CTRC and exons 4, 9, 10 and 11 of CFTR were analysed by Sanger sequencing in the index patients from both families. Large unbalanced rearrangements in PRSS1 and SPINK1 were excluded by Multiplex Ligation-Dependent Probe Amplification (MRC Holland). In the rest of the affected and unaffected family members, sequencing of exon 8 of CPA1 and exon 3 of CTRC was performed. In Family 1, all three affected individuals and the unaffected grandfather of the index patient (age 83 years) were heterozygous for the p.Ser282Pro CPA1 variant (figure 1). All other unaffected individuals available for testing did not carry the CPA1 variant. In Family 2, the index patient inherited the p.Ser282Pro CPA1 variant from the affected mother and the heterozygous c.180C>T (p.Gly60=) CTRC variant from the affected father who was negative for the CPA1 variant (figure 1). The heterozygous p.Gly60= CTRC variant is a weak CP risk factor increasing the disease risk about twofold. No other pathogenic variants were identified in the susceptibility genes tested in the index patients of the two families.
The functional effects of the p.Ser282Pro CPA1 variant were compared with those of the pathogenic variant p.Asn256Lys previously shown to cause misfolding and ER stress.2 Human embryonic kidney (HEK) 293T cells transfected with wild-type and mutant CPA1 constructs only secreted the wild-type proenzyme (figure 2A), while both mutants were retained intracellularly and suffered degradation, indicative of misfolding (figure 2B). Importantly, variants p.Ser282Pro and p.Asn256Lys induced ER stress to a comparable extent as judged by elevated mRNA levels of the chaperone BiP and increased splicing of the XBP1 mRNA relative to wild type (figure 2C).
In conclusion, we demonstrated that the novel p.Ser282Pro CPA1 variant causes hereditary CP by inducing ER stress in a similar manner to the previously reported misfolding p.Leu104Pro PRSS1 variant. The observations indicate that misfolding PRSS1 and CPA1 variants are similarly strong risk factors and ER stress is a highly relevant pathological mechanism in CP as suggested by Németh et al.1 and Witt et al.2
AAK and DB are equally contributing first authors.
MS-T and AMR are equally contributing senior authors.
Contributors Study concept, design and supervision: AMR and MS-T. Acquisition and analysis of genetic data: AAK, AMR, JA, KW-T and JB. Functional analysis: DB and MS-T. Patient enrolment, clinical data collection and interpretation: GO, KW and EK. Drafting the manuscript: AMR, AAK, MS-T and DB. Final approval of manuscript as submitted: all authors. AMR and MS-T contributed equally to this study. The first authors AAK and DB contributed equally to the laboratory experiments.
Funding This study was supported by the National Science Centre, Poland, grant 2015/19/B/NZ5/02224 (to AMR) and National Institutes of Health grant R01 DK058088 (to MS-T).
Competing interests None declared.
Ethics approval The study was approved by the Committee on Bioethics at Institute of Mother and Child (approval 28/2016).
Provenance and peer review Not commissioned; internally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.