Linkage studies in a large kindred with hereditary pancreatitis confirms mapping of the gene to a 16-cM region on 7q

Expanding ACMG variant classification guidelines into a general framework

BACKGROUND

The American College of Medical Genetics and Genomics (ACMG)-recommended five variant classification categories (pathogenic, likely pathogenic, uncertain significance, likely benign, and benign) have been widely used in medical genetics. However, these guidelines are fundamentally constrained in practice owing to their focus upon Mendelian disease genes and their dichotomous classification of variants as being either causal or not. Herein, we attempt to expand the ACMG guidelines into a general variant classification framework that takes into account not only the continuum of clinical phenotypes, but also the continuum of the variants' genetic effects, and the different pathological roles of the implicated genes.

MAIN BODY

As a disease model, we employed chronic pancreatitis (CP), which manifests clinically as a spectrum from monogenic to multifactorial. Bearing in mind that any general conceptual proposal should be based upon sound data, we focused our analysis on the four most extensively studied CP genes, PRSS1, CFTR, SPINK1 and CTRC. Based upon several cross-gene and cross-variant comparisons, we first assigned the different genes to two distinct categories in terms of disease causation: CP-causing (PRSS1 and SPINK1) and CP-predisposing (CFTR and CTRC). We then employed two new classificatory categories, "predisposing" and "likely predisposing", to replace ACMG's "pathogenic" and "likely pathogenic" categories in the context of CP-predisposing genes, thereby classifying all pathologically relevant variants in these genes as "predisposing". In the case of CP-causing genes, the two new classificatory categories served to extend the five ACMG categories whilst two thresholds (allele frequency and functional) were introduced to discriminate "pathogenic" from "predisposing" variants.

CONCLUSION

Employing CP as a disease model, we expand ACMG guidelines into a five-category classification system (predisposing, likely predisposing, uncertain significance, likely benign, and benign) and a seven-category classification system (pathogenic, likely pathogenic, predisposing, likely predisposing, uncertain significance, likely benign, and benign) in the context of disease-predisposing and disease-causing genes, respectively. Taken together, the two systems constitute a general variant classification framework that, in principle, should span the entire spectrum of variants in any disease-related gene. The maximal compliance of our five-category and seven-category classification systems with the ACMG guidelines ought to facilitate their practical application.

Hereditary Pancreatitis-25 Years of an Evolving Paradigm: Frank Brooks Memorial Lecture 2021

ABSTRACT

The identification of the genetic basis of hereditary pancreatitis in 1996 confirmed the critical role of trypsinogen in this disease and opened a new avenue of research on pancreatitis-associated genetic risk factors and their mechanism of action. Through the following 25 years, the ensuing discoveries fundamentally changed our understanding of pancreatitis pathogenesis, clarified the role of trypsinogen autoactivation in disease onset and progression, and set the stage for future therapeutic interventions. This Frank Brooks Memorial Lecture was delivered on November 4, 2021, at the 52nd Annual Meeting of the American Pancreatic Association, held in Miami Beach, Florida.

Trypsinogen (PRSS1 and PRSS2) gene dosage correlates with pancreatitis risk across genetic and transgenic studies: a systematic review and re-analysis

Trypsinogen (PRSS1, PRSS2) copy number gains and regulatory variants have both been proposed to elevate pancreatitis risk through a gene dosage effect (i.e., by increasing the expression of wild-type protein). However, to date, their impact on pancreatitis risk has not been thoroughly evaluated whilst the underlying pathogenic mechanisms remain to be explicitly investigated in mouse models. Genetic studies of the rare trypsinogen duplication and triplication copy number variants (CNVs), and the common rs10273639C variant, were collated from PubMed and/or ClinVar. Mouse studies that analyzed the influence of a transgenically expressed wild-type human PRSS1 or PRSS2 gene on the development of pancreatitis were identified from PubMed. The genetic effects of the different risk genotypes, in terms of odds ratios, were calculated wherever appropriate. The genetic effects of the rare trypsinogen duplication and triplication CNVs were also evaluated by reference to their associated disease subtypes. We demonstrate a positive correlation between increased trypsinogen gene dosage and pancreatitis risk in the context of the rare duplication and triplication CNVs, and between the level of trypsinogen expression and disease risk in the context of the heterozygous and homozygous rs10273639C-tagged genotypes. We retrospectively identify three mouse transgenic studies that are informative in relation to the pathogenic mechanism underlying the trypsinogen gene dosage effect in pancreatitis. Trypsinogen gene dosage correlates with pancreatitis risk across genetic and transgenic studies, highlighting the fundamental role of dysregulated expression of wild-type trypsinogen in the etiology of pancreatitis. Specifically downregulating trypsinogen expression in the pancreas may serve as a potential therapeutic and/or prevention strategy for pancreatitis.

The reversion variant (p.Arg90Leu) at the evolutionarily adaptive p.Arg90 site in CELA3B predisposes to chronic pancreatitis

A gain-of-function missense variant in the CELA3B gene, p.Arg90Cys (c.268C>T), has recently been reported to cause pancreatitis in an extended pedigree. Herein, we sequenced the CELA3B gene in 644 genetically unexplained French chronic pancreatitis (CP) patients (all unrelated) and 566 controls. No obvious loss-of-function variants were identified. None of the six low-frequency or common missense variants detected showed significant association with CP. Nor did the aggregate rare/very rare missense variants (n = 14) show any significant association with CP. However, p.Arg90Leu (c.269G>T), which was found in four patients but no controls, and affects the same amino acid as p.Arg90Cys, serves to revert p.Arg90 to the human elastase ancestral allele. As p.Arg90Leu has previously been shown to exert a similar functional effect to that of p.Arg90Cys, our findings not only confirm the involvement of CELA3B in the etiology of CP but also pinpoint a new evolutionarily adaptive site in the human genome.

Trypsin activity governs increased susceptibility to pancreatitis in mice expressing human PRSS1R122H

Currently, an effective targeted therapy for pancreatitis is lacking. Hereditary pancreatitis (HP) is a heritable, autosomal-dominant disorder with recurrent acute pancreatitis (AP) progressing to chronic pancreatitis (CP) and a markedly increased risk of pancreatic cancer. In 1996, mutations in PRSS1 were linked to the development of HP. Here, we developed a mouse model by inserting a full-length human PRSS1R122H gene, the most commonly mutated gene in human HP, into mice. Expression of PRSS1R122H protein in the pancreas markedly increased stress signaling pathways and exacerbated AP. After the attack of AP, all PRSS1R122H mice had disease progression to CP, with similar histologic features as those observed in human HP. By comparing PRSS1R122H mice with PRSS1WT mice, as well as enzymatically inactivated Dead-PRSS1R122H mice, we unraveled that increased trypsin activity is the mechanism for R122H mutation to sensitize mice to the development of pancreatitis. We further discovered that trypsin inhibition, in combination with anticoagulation therapy, synergistically prevented progression to CP in PRSS1R122H mice. These animal models help us better understand the complex nature of this disease and provide powerful tools for developing and testing novel therapeutics for human pancreatitis.

Alcohol Consumption and Cigarette Smoking are Important Modifiers of the Association Between Acute Pancreatitis and the PRSS1-PRSS2 Locus in Men

OBJECTIVES

The present study was designed to investigate whether the susceptibility to acute pancreatitis (AP) attributable to polymorphism rs10273639 at the PRSS1-PRSS2 locus is dependent on alcohol consumption and cigarette smoking.

METHODS

A total of 603 unrelated Russian individuals including 304 patients with physician-diagnosed AP and 299 sex- and age-matched healthy controls have been recruited for the study. A polymorphism rs10273639 (-408C>T) of PRSS1-PRSS2 was genotyped by TaqMan-based assay.

RESULTS

A variant allele -408T (P = 0.003) and genotypes -408CT plus TT (P = 0.002) were associated with decreased AP risk only in men. The odds ratios for AP in the CC homozygotes versus the variant genotypes were 1.95 [95% confidence interval (CI), 0.65-5.85; P = 0.23], 1.72 (95% CI, 0.93-3.20; P = 0.08), and 2.37 (95% CI, 1.09-5.13; P = 0.03) for men who consumed up to 28, 29 to 59, and more than 60 alcohol drinks a week, respectively. Cigarette smokers with the -408CC genotype had an increased risk of AP (odds ratio, 2.07; 95% CI, 1.25-3.42; P = 0.004), whereas nonsmoker carriers did not have a disease risk (odds ratio, 1.48; 95% CI, 0.58-3.82; P = 0.42).

CONCLUSIONS

We confirmed a robust association of polymorphism rs10273639 at PRSS1-PRSS2 with AP in the Russian population. The present study is the first to show that relationship between the locus and disease is significantly modified by alcohol consumption and cigarette smoking.

Hereditary pancreatitis: current perspectives

Hereditary pancreatitis (HP) is a rare cause of acute, recurrent acute, and chronic pancreatitis. It may present similarly to other causes of acute and chronic pancreatitis, and often there has been a protracted evaluation prior to the diagnosis of HP. Since it was first described in 1952, multiple genetic defects that affect the action of digestive enzymes in the pancreas have been implicated. The most common mutations involve the PRSS1, CFTR, SPINK1, and CTRC genes. New mutations in these genes and previously unrecognized mutations in other genes are being discovered due to the increasing use of next-generation genomic sequencing. While the inheritance pathways of these genetic mutations may be variable and complex, sometimes involving coinheritance of other mutations, the clinical presentation of patients tends to be similar. Interactions with environmental triggers often play a role. Patients tend to present at an early age (prior to the second decade of life) and have a significantly increased risk for the development of pancreatic adenocarcinoma. Patients with HP may develop sequelae of chronic pancreatitis such as strictures and fluid collections as well as exocrine and endocrine insufficiency. Management of patients with HP involves avoidance of environmental triggers, surveillance for pancreatic adenocarcinoma, medical therapy for endocrine and exocrine insufficiency, pain management, and endoscopic or surgical treatment for complications. Care for affected patients should be individualized, with an emphasis on early diagnosis and multidisciplinary involvement to develop a comprehensive treatment strategy.

Human cationic trypsinogen (PRSS1) variants and chronic pancreatitis

Variations in the serine protease 1 (PRSS1) gene encoding human cationic trypsinogen have been conclusively associated with autosomal dominant hereditary pancreatitis and sporadic nonalcoholic chronic pancreatitis. Most high-penetrance PRSS1 variants increase intrapancreatic trypsin activity by stimulating trypsinogen autoactivation and/or by inhibiting chymotrypsin C-dependent trypsinogen degradation. Alternatively, some PRSS1 variants can cause trypsinogen misfolding, which results in intracellular retention and degradation with consequent endoplasmic reticulum stress. However, not all PRSS1 variants are pathogenic, and clinical relevance of rare variants is often difficult to ascertain. Here we review the PRSS1 variants published since 1996 and discuss their functional properties and role in chronic pancreatitis.

Involvement of inflammatory factors in pancreatic carcinogenesis and preventive effects of anti-inflammatory agents

Chronic inflammation is known to be a risk for many cancers, including pancreatic cancer. Heavy alcohol drinking and cigarette smoking are major causes of pancreatitis, and epidemiological studies have shown that smoking and chronic pancreatitis are risk factors for pancreatic cancer. Meanwhile, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) are elevated in pancreatitis and pancreatic cancer tissues in humans and in animal models. Selective inhibitors of iNOS and COX-2 suppress pancreatic cancer development in a chemical carcinogenesis model of hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). In addition, hyperlipidemia, obesity, and type II diabetes are also suggested to be associated with chronic inflammation in the pancreas and involved in pancreatic cancer development. We have shown that a high-fat diet increased pancreatic cancer development in BOP-treated hamsters, along with aggravation of hyperlipidemia, severe fatty infiltration, and increased expression of adipokines and inflammatory factors in the pancreas. Of note, fatty pancreas has been observed in obese and/or diabetic cases in humans. Preventive effects of anti-hyperlipidemic/anti-diabetic agents on pancreatic cancer have also been shown in humans and animals. Taking this evidence into consideration, modulation of inflammatory factors by anti-inflammatory agents will provide useful data for prevention of pancreatic cancer.

An overview of hereditary pancreatitis

Hereditary pancreatitis is a rare cause of chronic pancreatitis. The prevalence was evaluated to 0.3/100000 in Western Countries. Genetic disorders are due to mutations of the PRSS1 gene on the long arm of the chromosome 7, encoding for the cationic trypsinogen. The inheritance pattern is autosomal dominant with an incomplete penetrance (80%). Since 1996, more than 30 mutations were found. The three more common mutations are R122H, N29I and A16V. First symptoms begin since childhood, mainly before 10 years old. Main symptoms are pancreatic pain and acute pancreatitis (>70%). CP morphological changes as pancreatic calcifications are diagnosed at a median age of 22-25 years. Exocrine and endocrine pancreatic insufficiency occurred in 34% and 26% at a median age of 29 and 38 years. No clinical differences exist according to the mutation type. No excess of mortality in hereditary pancreatitis population compared to general population was found, despite a real risk of cancer. The cumulative risks of pancreatic cancer at 50, 60 and, 75 years are 10%, 18.7% and, 53.5%, respectively. The relative risk of cancer increases in smokers and is evaluated to 8.55. Hereditary pancreatitis diagnosis permits to propose an adapted management in expert centres.

Interaction between a novel intronic IVS3+172 variant and N29I mutation in PRSS1 gene is associated with pancreatitis in a Malaysian Chinese family

BACKGROUND/AIMS

Hereditary pancreatitis (HP) is a very rare form of early-onset chronic pancreatitis, which usually begins in childhood with a variable spectrum of severity of disease. HP is commonly caused by variants/mutations in the PRSS1 gene as reported in many studies. Therefore, in this study, we aimed to investigate the possible association of PRSS1 gene variants/mutations in a Malaysian Chinese family with HP.

METHODS

Genomic DNA of the 6 family members was extracted, amplified using polymerase chain reaction and the entire PRSS1 gene was analyzed via sequencing.

RESULTS

PRSS1 gene sequencing results revealed two variants/mutations in this study. The results show that all the subjects (patients) inherited an intronic SNP IVS3+172 variant, together with a p.N29I mutation except for subjects 3 and 4 who are normal.

CONCLUSION

We believe that interaction between the novel IVS3+172 intronic variant and p.N29I mutation in the PRSS1 gene is associated with HP in this Malaysian Chinese family.

Chymotrypsin C mutations in chronic pancreatitis

Chronic pancreatitis is a persistent inflammatory disorder characterized by destruction of the pancreatic parenchyma, maldigestion, and chronic pain. Mutations in the chymotrypsin C (CTRC) gene encoding the digestive enzyme CTRC have been shown to increase the risk of chronic pancreatitis in European and Asian populations. Here, we review the biochemical properties and physiological functions of human CTRC, summarize the functional defects associated with CTRC mutations, and discuss mechanistic models that might explain the increased disease risk in carriers.

Hereditary pancreatitis

Hereditary chronic pancreatitis (HCP) is a rare disease in which chronic pancreatitis develops in childhood. HCP has autosomal dominant inheritance with approximately 80% penetrance. Diagnostic criteria are not universally agreed upon but the EUROPAC trial defined it as two first-degree relatives or at least 3 second-degree relatives in two or more generations, with chronic pancreatitis for which there is no other etiology. The gene for HCP was originally identified on chromosome 7 and subsequently many other genes have been reported to be associated with HCP. To date, no single genetic alteration has been found that is necessary for the development of HCP. In a recent study, 81% of patients with HCP were found to have a mutation of the PRSS1 gene. Patients with HCP are at risk for developing exocrine and endocrine insufficiency and there is a 50-fold increased risk of pancreatic cancer in HCP patients as compared with the general population.

Genetic factors in chronic pancreatitis; implications for diagnosis, management and prognosis

Chronic pancreatitis (CP) is a clinical situation with persisting inflammation leading to destruction of the pancreas ensuing endocrine and exocrine failure. There are 4 subtypes: hereditary, idiopathic, alcoholic and tropical pancreatitis. Genetic factors can explain a significant proportion of CP cases. The PRSS1 gene, encoding cationic trypsinogen, was found to be correlated with hereditary CP. This signalled the extensive search for other candidate genes within the trypsin pathway. Genes like SPINK1 and CTRC are associated with CP and should be considered as important contributing factors rather than causative. The search for candidate genes not part of the trypsin pathway has been less successful and the only gene consistently associated with CP is the Cystic Fibrosis Transmembrane Regulator. In this review we will discuss the various CP subtypes in relation to the respective genetic variants. This review will also address the implications of genetic testing in daily clinical practise.

Prevalence of pancreatic diabetes in patients carrying mutations or polymorphisms of the PRSS1 gene in the Han population

OBJECTIVE

This study updated the estimated prevalence of type 3c diabetes damage to the pancreas through different genotypes of PRSS1 and their clinical characteristics in the Han population.

SUBJECTS AND METHODS

Cross-sectional analysis was performed of the most recent (2003-2007) patients with pancreatitis from six hospitals of the Han population in South China (n = 253).

RESULTS

There were 32 patients with pancreatitis carrying a PRSS1 gene abnormality within intron region among 253 cases of pancreatitis, including 27 patients carrying novel single nucleotide polymorphisms, namely, IVS 3 +75 A --> G conversion, and five patients with the mutation IVS3 + 10 T --> G. Among these patients, there were only three cases of patients with diabetes (9.37%). This was lower than the prevalence of abnormalities in the exons of the PRSS1 gene (51.92%): 12 patients with c.361 G --> A, eight patients with c.415 T --> A, and five patients with c.365G --> A. Among them were 12 persons with diabetes, including five requiring insulin to regulate blood sugar. What is more, among the 27 patients carrying PRSS1 gene polymorphism (c.486 C --> T, within the exon 4), there were 15 persons with diabetes symptoms. More than 40% of these patients required insulin to regulate blood sugar.

CONCLUSIONS

An abnormality within the intron region of the PRSS1 gene represents one of the causes of pancreatitis in Chinese patients, but it is not related to pancreatic diabetes. However, the exon abnormality obviously raises the morbidity rate of type 3c diabetes, which relies on insulin.

Mortality rate and risk factors in patients with hereditary pancreatitis: uni- and multidimensional analyses

OBJECTIVES

Patients with hereditary pancreatitis (HP) bear a high risk of pancreatic adenocarcinoma, but their life expectancy remains unknown. The objective of the study was to assess whether the high risk of cancer decreases survival.

METHODS

Inclusion criteria were the presence of a PRSS1 mutation with pancreatic symptoms or chronic pancreatitis in at least two first-degree relatives or three second-degree relatives without another cause. Survival rates were assessed according to risk factors. Excess mortality compared with the general French population was calculated (statistical Esteve model) for two periods (20-50 and 50-70 years), according to several risk factors.

RESULTS

The cohort comprised 189 patients. PRSS1 mutations were found in 66%. A total of 19 patients died at the median age of 60. In all, 10 deaths were attributable to HP, including 8 to pancreatic adenocarcinoma. Median overall survival for the whole cohort was 74 years (95% confidence interval (CI): 71-79). The presence of R122H mutation, gender, tobacco consumption in patients older than 18 years, and diabetes mellitus were not associated with differences in survival. Only patients with pancreatic cancer had decreased survival (P=0.008). Excess mortality risk compared with the general population was 0.02% between 20 and 50 years, and 0.61% between 50 and 70 years (NS). Gender, R122H mutation, diabetes, and tobacco use were not associated with excess mortality in these two periods.

CONCLUSIONS

Despite their high risk of cancer, HP patients do not have excess mortality risk compared with the general population, irrespective of gender, tobacco use, or diabetes mellitus. These data should be brought to the patient's attention.

The recognition and surgical management of heritable lesions of the pancreas

Our knowledge regarding the inherited factors that lead to the development of lesions within the pancreas is clearly incomplete. This article addresses clinical issues in patients at moderate-to-high risk for pancreatic malignancy, with special emphasis on the recognition and diagnosis of known genetic syndromes. Using the current available information, the authors attempt to equip the practicing surgeon with critical information to increase clinical suspicion for heritable syndromes and inform specific surgical management. Additionally, this article is meant to encourage the practicing surgeon to participate in the genetic testing/screening, cancer surveillance, and prevention activities of patients who have heritable cancer syndromes and associated pancreatic lesions that require surgery.

Chronic pancreatitis: genetics and pathogenesis

Chronic pancreatitis (CP) is a persistent inflammation of the pancreas. Over the past 12 years, genetic studies of hereditary, familial, and idiopathic forms of CP have made great progress in defining the disease pathogenesis. Identification of gain-of-function missense and copy number mutations in the cationic trypsinogen gene (PRSS1) and loss-of-function variants in both the pancreatic secretory trypsin inhibitor (SPINK1) and chymotrypsinogen C (CTRC) genes has firmly established the pivotal role of prematurely activated trypsin within the pancreas in the etiology of CP. Loss-of-function variants in the cystic fibrosis transmembrane conductance regulator (CFTR) and calcium-sensing receptor (CASR) genes also increase the risk of CP. Here, we review recent developments in this rapidly evolving field, highlight the importance of gene-gene and gene-environment interactions in causing the disease, and discuss the opportunities and challenges in identifying novel genetic factors that affect susceptibility/resistance to CP.

Clinical and hereditary characteristics of hereditary pancreatitis: an analysis of 13 cases

AIM: To study the clinical manifestations and genetic characterisitcs of hereditary pancreatitis (HP).

METHODS: We retrospectively reviewed the clinical data of 13 HP patients (10 from 3 families, and 3 sporadic cases).

RESULTS: The ages of the 10 patients from 3 families ranged from 8 to 48 years old (7 cases less than 20 years old and 3 cases more than 20 years old), and the mutation of protease serine 1 (PRSS1) gene occurred frequently. The clinical manifestations were various and recurrent abdominal pain was an important sign. Dominant heredity was the genetic character, and HP occurred earlier in the next generation. The 3 sporadic cases were all above 25 years old.

CONCLUSION: HP has various clinical manifestations and genetic anticipation characteristic.

Hereditary chronic pancreatitis

Hereditary chronic pancreatitis (HCP) is a very rare form of early-onset chronic pancreatitis. Apart from young age at diagnosis and a slower progression, the clinical course, morphological features and laboratory findings of HCP do not differ from those of patients with alcoholic chronic pancreatitis. Diagnostic criteria and treatment of HCP also resemble those of chronic pancreatitis of other causes. The clinical presentation is highly variable and includes chronic abdominal pain, impairment of endocrine and exocrine pancreatic function, nausea and vomiting, maldigestion, diabetes, pseudocysts, bile-duct and duodenal obstruction, and rarely pancreatic cancer. Fortunately, the disease is mild in most patients. Mutations in the PRSS1 gene, encoding cationic trypsinogen, play a causative role in chronic pancreatitis. It has been shown that the PRSS1 mutations increase autocatalytic conversion of trypsinogen to active trypsin, and thus probably cause premature, intrapancreatic trypsinogen activation, disturbing the intrapancreatic balance of proteases and their inhibitors. Other genes--such as the anionic trypsinogen (PRSS2), the serine protease inhibitor Kazal type 1 (SPINK1), and the cystic fibrosis transmembrane conductance regulator (CFTR)--have also been found to be associated with chronic pancreatitis (idiopathic and hereditary). Genetic testing should only be performed in carefully selected patients by direct DNA sequencing, and antenatal diagnosis should not be encouraged. Treatment focuses on enzyme and nutritional supplementation, pain management, pancreatic diabetes, and local organ complications such as pseudocysts and bile-duct or duodenal obstruction. The disease course and prognosis of patients with HCP is unpredictable. The risk of pancreatic cancer is elevated. Therefore, HCP patients should strongly avoid environmental risk factors for pancreatic cancer.

Association of rare chymotrypsinogen C (CTRC) gene variations in patients with idiopathic chronic pancreatitis

Extensive genetic studies of chronic pancreatitis over the past decade have highlighted the importance of a tightly regulated balance between activation and inactivation of trypsin within the pancreas to disease susceptibility and resistance. The recent identification of chymotrypsin C (CTRC) as enzyme Y, which was proposed to protect the pancreas by degrading prematurely activated trypsinogen within the pancreas 20 years ago, made CTRC an excellent candidate gene for disease-association studies. Here, we analyzed all eight exons of the CTRC gene for conventional genetic variants and copy number variations (CNVs) by direct sequencing and quantitative fluorescent multiplex PCR, respectively, in a total of 287 French white patients (idiopathic x 216; familial x 42; hereditary x 29). While no CNVs were found in any of the 287 subjects, 20 conventional variations including a nonsense mutation (p.W55X), a microdeletion mutation (p.K247_R254del) and nine missense mutations were found in the 216 patients with idiopathic chronic pancreatitis (ICP). Except for two common polymorphisms, all the remaining 18 mutational events represent rare variations, with a minor allele frequency of 0-0.3% in the control population. All these rare variants were always found more frequently in the ICP patients than in the controls, and their combined frequency in the ICP patients (26/216; 12.0%) is significantly different from that in the controls (4/350; 1.1%) (OR = 11.8 [3.9-40.6]), chi (2) = 31.58, P < 10(-6)). This genetic finding, when considered in the perceived role of CTRC in eliminating prematurely activated trypsin, indicated that CTRC is a new pancreatitis susceptibility gene.

Trypsinogen copy number mutations in patients with idiopathic chronic pancreatitis

BACKGROUND & AIMS

We have recently reported that the triplication of a approximately 605 kilobase segment containing the PRSS1 (encoding cationic trypsinogen) and PRSS2 (encoding anionic trypsinogen) genes causes hereditary pancreatitis. Here we went further to investigate whether this copy number mutation could account for some unidentified French white patients with idiopathic chronic pancreatitis (ICP) or familial chronic pancreatitis (FCP) as well as Indian patients with tropical calcific pancreatitis (TCP).

METHODS

Patients and controls were screened by means of previously described quantitative fluorescent multiplex polymerase chain reaction and/or genotyping of the microsatellite marker rs3222967.

RESULTS

The approximately 605 kilobase triplication and a novel duplication (confirmed by fluorescence in situ hybridization) of the trypsinogen locus were detected in 10 and 2 of 202 ICP patients, respectively (age of disease onset, <or=20 years) but were absent in 282 French controls. In addition, the duplication mutation was found in 2 of 1044 ICP patients whose age of disease onset was >20 years. However, the 2 trypsinogen copy number mutations were observed in neither 103 FCP patients nor 268 Indian TCP patients.

CONCLUSIONS

Our findings revealed the molecular basis of 6% of the young ICP patients and further demonstrated that chronic pancreatitis is a genomic disorder. Our findings also add to the mounting evidence showing that trypsinogen gene mutations do not appear to play an important role in the pathogenesis of TCP in the Indian population. Finally, a dividend of this study is that we have provided convincing evidence to show that all 5 previously described copy number variations involving PRSS1 or/and PRSS2 are artifacts.

Screening for human cationic trypsinogen (PRSS1) and trypsinogen inhibitor gene (SPINK1) mutations in a Finnish family with hereditary pancreatitis

OBJECTIVE

Mutations in the cationic trypsinogen gene (PRSS1) have been linked with hereditary pancreatitis (HP). A change in R122H in the third exon is one of the mutations most frequently associated with HP. A mutation N34S in the serine protease inhibitor Kazal type 1 gene has also been shown to be linked with HP. The purpose of this study was to report on the incidence of PRSS1 and SPINK1 mutations in a Finnish family with HP and to correlate the findings to the clinical symptoms.

MATERIAL AND METHODS

The study included 36 individuals from one Finnish family with HP (21 M, 15 F, median age 38 years). All individuals underwent abdominal ultrasound and laboratory tests (glucose, faecal elastase-1 test). Blood samples were taken for mutational analysis of PRSS1 (R122H, N29I and A16V) and SPINK1 (N34S).

RESULTS

Ten (28%) individuals were affected by mutations: the most frequent mutation was R122H, affecting 8 (22%) individuals; 2 (6%) individuals were affected by the N34S mutation and none by the other tested mutations (N29I and A16V). Four out of eight (50%) R122H-positive individuals had a diagnosis of chronic pancreatitis without other known aetiologies. Four out of five (80%) male individuals with the R122H mutation also had clinical pancreatitis, whereas none of the three mutation-positive females had any signs or symptoms of chronic pancreatitis. The two individuals with the N34S mutation did not have any signs of chronic pancreatitis.

CONCLUSIONS

In the investigated Finnish pedigree with HP, the PRSS1 mutation R122H is linked with chronic disease. Although the SPINK1 mutation (N34S) was also observed in two individuals, it was not linked with the disease.

Functional analysis of pancreatitis-associated missense mutations in the pancreatic secretory trypsin inhibitor (SPINK1) gene

Variations in the SPINK1 gene (encoding pancreatic secretory trypsin inhibitor (PSTI)) are associated with chronic pancreatitis. We have recently determined the functional consequences of three missense mutations that occurred within the signal peptide sequence of PSTI by Western blotting analysis of wild-type and mutant PSTI expressed in Chinese hamster ovary cells. Here, this approach was extended to analyze seven missense mutations (p.N34S, p.G48E, p.D50E, p.Y54H, p.P55S, p.R65Q and p.R67C) occurring within the mature peptide of PSTI. This analysis enabled us to classify these missense mutations into three categories. The first category comprises the p.N34S and p.P55S polymorphisms, both of which occur in evolutionarily non-conserved residues, involve amino-acid substitutions with similar physicochemical properties, and do not cause any significant reduction in terms of PSTI mature peptide expression. The second category contains only the p.R65Q missense mutation, which occurs in a well-conserved residue, involves the substitution of a positively charged amino acid by a non-charged one, and causes a approximately 60% reduction of protein expression. The third category comprises p.G48E, p.D50E, p.Y54H, and p.R67C, all of which occur in strictly conserved residues, involve charged amino acids, and cause complete or nearly complete loss of PSTI expression. Having excluded the possibility that the reduced protein expression may have resulted from reduced transcription or unstable mRNA, we surmise that these missense mutations probably cause intracellular retention of their respective mutant proteins. This is suggestive of a potential unifying pathological mechanism underlying both the signal peptide and mature peptide mutations.

Genetic counseling for nonsyndromic pancreatitis

An appreciation for the background of disease, not to mention the medical management of individuals, may be significantly affected by testing for mutations and genetic variants associated with pancreatitis. Pretest and posttest counseling are essential for patients and families to benefit fully from genetic testing for a susceptibility to develop pancreatitis. The clinician, often working directly with a qualified genetic counselor, must ensure that patients and families appreciate the benefits and limitations of genetic tests, that results are interpreted accurately, and that patients understand implications of information for both their medical care and personal decisions. This article focuses on the approach to genetic counseling for pancreatitis and implications of recent advances.

Hereditary chronic pancreatitis

Hereditary chronic pancreatitis (HCP) is a very rare form of early onset chronic pancreatitis. With the exception of the young age at diagnosis and a slower progression, the clinical course, morphological features and laboratory findings of HCP do not differ from those of patients with alcoholic chronic pancreatitis. As well, diagnostic criteria and treatment of HCP resemble that of chronic pancreatitis of other causes. The clinical presentation is highly variable and includes chronic abdominal pain, impairment of endocrine and exocrine pancreatic function, nausea and vomiting, maldigestion, diabetes, pseudocysts, bile duct and duodenal obstruction, and rarely pancreatic cancer. Fortunately, most patients have a mild disease. Mutations in the PRSS1 gene, encoding cationic trypsinogen, play a causative role in chronic pancreatitis. It has been shown that the PRSS1 mutations increase autocatalytic conversion of trypsinogen to active trypsin, and thus probably cause premature, intrapancreatic trypsinogen activation disturbing the intrapancreatic balance of proteases and their inhibitors. Other genes, such as the anionic trypsinogen (PRSS2), the serine protease inhibitor, Kazal type 1 (SPINK1) and the cystic fibrosis transmembrane conductance regulator (CFTR) have been found to be associated with chronic pancreatitis (idiopathic and hereditary) as well. Genetic testing should only be performed in carefully selected patients by direct DNA sequencing and antenatal diagnosis should not be encouraged. Treatment focuses on enzyme and nutritional supplementation, pain management, pancreatic diabetes, and local organ complications, such as pseudocysts, bile duct or duodenal obstruction. The disease course and prognosis of patients with HCP is unpredictable. Pancreatic cancer risk is elevated. Therefore, HCP patients should strongly avoid environmental risk factors for pancreatic cancer.

Mutations of human cationic trypsinogen (PRSS1) and chronic pancreatitis

Ten years ago, the groundwork for the discovery of the genetic basis of chronic pancreatitis was laid by linkage analyses of large kindreds with autosomal dominant hereditary chronic pancreatitis. Subsequent candidate gene sequencing of the 7q35 chromosome region revealed a strong association of the c.365G > A (p.R122 H) mutation of the PRSS1 gene encoding cationic trypsinogen with hereditary pancreatitis. In the following years, further mutations of this gene were discovered in patients with hereditary or idiopathic chronic pancreatitis. In vitro the mutations increase autocatalytic conversion of trypsinogen to active trypsin and thus probably cause premature, intrapancreatic trypsinogen activation in vivo. The clinical presentation is highly variable, but most affected mutation carriers have relatively mild disease. In this review, we summarize the current knowledge on trypsinogen mutations and their role in pancreatic diseases.

Hereditary pancreatitis in a family of Aboriginal descent

Hereditary pancreatitis is an autosomal dominant condition characterized by recurrent episodes of acute pancreatitis, usually starting in childhood. We present a family who was ascertained when an 11-year-old girl presented with an episode of acute pancreatitis. Her father and other family members had also had recurrent bouts of acute pancreatitis. Genetic testing revealed a pathogenic mutation in the cationic trypsinogen gene in the proband, her father and her paternal grandmother. As far as we are aware, this is the first Aboriginal kindred with mutation-proven hereditary pancreatitis. Hereditary pancreatitis is an important differential diagnosis to consider in a patient with recurrent episodes of acute pancreatitis with no obvious precipitating cause. This family is of Aboriginal descent and the implications of the family's background are also discussed when considering the aetiology of the condition. We emphasize the need to ascertain a full family history from patients with a history of repeated episodes of acute pancreatitis and also emphasize the need to avoid ethnic stereotypes when assessing patients.

A novel mutation of the calcium sensing receptor gene is associated with chronic pancreatitis in a family with heterozygous SPINK1 mutations

Background

The role of mutations in the serine protease inhibitor Kazal type 1 (SPINK1) gene in chronic pancreatitis is still a matter of debate. Active SPINK1 is thought to antagonize activated trypsin. Cases of SPINK1 mutations, especially N34S, have been reported in a subset of patients with idiopathic chronic pancreatitis. However, the inheritance pattern is still unknown. Some cases with N34S heterozygosity have been reported with and without evidence for CP indicating neither an autosomal recessive nor dominant trait. Therefore SPINK1 mutations have been postulated to act as a disease modifier requiring additional mutations in a more complex genetic model. Familial hypocalciuric hypercalcemia (FHH) caused by heterozygous inactivating mutations in the calcium sensing receptor (CASR) gene is considered a benign disorder with elevated plasma calcium levels. Although hypercalcemia represents a risk factor for pancreatitis, increased rates of pancreatitis in patients with FHH have not been reported thus far.

Methods

We studied a family with a FHH-related hypercalcemia and chronic pancreatitis. DNA samples were analysed for mutations within the cationic trypsinogen (N29I, R122H) and SPINK1 (N34S) gene using melting curve analysis. Mutations within CASR gene were identified by DNA sequencing.

Results

A N34S SPINK1 mutation was found in all screened family members. However, only two family members developed chronic pancreatitis. These patients also had FHH caused by a novel, sporadic mutation in the CASR gene (518T>C) leading to an amino acid exchange (leucine->proline) in the extracellular domain of the CASR protein.

Conclusion

Mutations in the calcium sensing receptor gene might represent a novel as yet unidentified predisposing factor which may lead to an increased susceptibility for chronic pancreatitis. Moreover, this family analysis supports the hypothesis that SPINK1 mutations act as disease modifier and suggests an even more complex genetic model in SPINK1 related chronic pancreatitis.

Genetic disorders of the pancreas

The venues opened to all by the remarkable studies of the genome are just starting to become manifest; they can now distinguish different variants of a disease; they are given the tools to better understand the pathophysiology of illness; they hope to be able to provide better treatment alternatives to our patients. The examples described in this review demonstrate the applicability of these concepts to pancreatic disorders. Researchers may be just scratching the surface at this time, but the potential is enormous. Many philosophic and ethical questions need to be answered as physicians move along: Should all family members of an index case be screened? Who should pay for testing? Who should get results? But, without the participation of so many patients, their family members, and numerous volunteers, researchers would not have witnessed the bridging of so many gaps as they have so far. All of us may now look forward to the application of this incredible knowledge to the therapeutic solutions so eagerly awaited.

Hereditary pancreatitis

Hereditary pancreatitis is an autosomal dominant condition, which results in recurrent attacks of acute pancreatitis, progressing to chronic pancreatitis often at a young age. The majority of patients with hereditary pancreatitis express one of two mutations (R122H or N29I) in the cationic trypsinogen gene (PRSS1 gene). It has been hypothesised that one of these mutations, the R122H mutation causes pancreatitis by altering a trypsin recognition site so preventing deactivation of trypsin within the pancreas and prolonging its action, resulting in autodigestion. Families with these two mutations have been identified in many countries and there are also other rarer mutations, which have also been linked to hereditary pancreatitis.

Patients with hereditary pancreatitis present in the same way as those with sporadic pancreatitis but at an earlier age. It is common for patients to remain undiagnosed for many years, particularly if they present with non-specific symptoms. Hereditary pancreatitis should always be considered in patients who present with recurrent pancreatitis with a family history of pancreatic disease. If patients with the 2 common mutations are compared, those with the R122H mutation are more likely to present at a younger age and are more likely to require surgical intervention than those with N29I. Hereditary pancreatitis carries a 40% lifetime risk of pancreatic cancer with those patients aged between 50 to 70 being most at risk in whom screening tests may become important.

Hereditary pancreatitis: a model for understanding the genetic basis of acute and chronic pancreatitis

Progress in understanding pancreatic diseases has been limited by a number of factors. Primary problems include the absence of good animal models, and difficulty in understanding the origin of pancreatic disease since the disease is usually manifest by the progressive destruction of the gland itself. Beginning in 1995, our laboratory, with the support of the Midwest Multicenter Pancreatic Study Group, began investigating the genetic basis of hereditary pancreatitis. Utilization of information becoming available through the human genome project allowed us to map and identify the hereditary pancreatitis gene as cationic trypsinogen (PRSS1). Molecular modeling, and subsequent experimental evidence, has solved key elements of the mysteries surrounding the origin of acute pancreatitis and the progression of acute pancreatitis to chronic pancreatitis. The availability of new genetic information and genomic tools should produce a revolution in our understanding of pancreatic diseases.

Genetic testing in acute and chronic pancreatitis

Hereditary pancreatitis (HP) is clinically indistinguishable from pancreatitis with other causes. Patients with HP have an increased chance of developing pancreatitis. Mutations in the cationic trypsinogen gene appear to cause most HP, although there is evidence for mild genetic heterogeneity with defects in other genes. Trypsin stabilization and protection from autolysis appear to play a central role in the pathogenesis of pancreatitis. The role of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) as well as the pancreatic secretory trypsin inhibitor (PSTI) in patients with pancreatitis is intriguing but as yet incompletely understood. Genetic testing may help to identify and manage patients with HP. Healthcare professionals should understand the elements necessary for obtaining informed consent for patients undergoing these tests, the limits in interpreting test results, and the psychosocial issues that may arise from genetic testing.

Differential expression of the cell-adhesion molecule Nr-CAM in hyperplastic and neoplastic human pancreatic tissue

Nr-CAM is a member of the immunoglobulin superfamily of neural cell-adhesion molecules initially thought to be expressed mainly in the brain. Here we show the presence of Nr-CAM protein in normal human pancreas and characterize its expression in hyperplastic and neoplastic human pancreatic tissue. Nr-CAM is expressed on the cell surface in normal pancreatic acini with enhanced staining at cell-cell junctions, and weak or no surface staining is seen on normal ductal cells. Nr-CAM expression is markedly up-regulated in intraductal hyperplasia. Expression was well maintained in well or moderately differentiated carcinoma but was reduced or absent from most poorly differentiated tumors. In addition, 4 of 4 human pancreatic adenocarcinoma cell lines tested demonstrated little or no Nr-CAM expression. This differential regulation of Nr-CAM expression suggests that it may be involved in the pathogenesis and invasive/metastatic behavior of pancreatic cancers. HUM PATHOL 32:396-400.

Pancreatitis in fibrocalculous pancreatic diabetes mellitus is not associated with common mutations in the trypsinogen gene

BACKGROUND

A distinct type of pancreatitis associated with diabetes, termed fibrocalculous pancreatic diabetes (FCPD), has been reported in tropical developing countries including Bangladesh. The molecular basis for autosomal dominant hereditary pancreatitis (HP) has recently been attributed to mutations in exons 2 and 3 of the trypsinogen gene. We have investigated the hypothesis that mutations in the aforementioned exons of this gene might also predispose to FCPD.

METHODS

Seventy Bangladeshi and 50 South Indian unrelated FCPD patients and seven South Indian families with FCPD probands were studied. Pancreatic calcification was confirmed by abdominal X-ray, ultrasound and/or ERCP. Established mutations of exons 2 and 3 of the trypsinogen gene were studied in these subjects by PCR-RFLP analysis and DNA sequencing.

RESULTS

The mutations found in hereditary pancreatitis were not observed in this collection of FCPD subjects, and complete DNA sequencing of exons 2 and 3 of the fourth cationic trypsinogen gene also excluded any new mutations.

CONCLUSIONS

These results indicate that chronic pancreatitis of FCPD is unlikely to be caused by common mutations in the trypsinogen gene.

Genetics of chronic pancreatitis

Chronic pancreatitis is an inflammatory disease causing structural and progressive damage resulting in permanent deficit of both the exocrine and endocrine components. Although a few risk factors for the disease are known, of which the primary one is alcohol consumption, the actual mechanisms responsible for the initial steps and evolution of the disease are not. The discovery of mutations in the cationic trypsinogen gene in patients with hereditary pancreatitis and a high incidence of mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR) in patients with chronic pancreatitis might be important clues to understanding the molecular mechanisms of this disease.

Mutations of the cationic trypsinogen in hereditary pancreatitis

Hereditary pancreatitis (OMIM 167800) is thought to be associated with a mutation of the exon 3 of cationic trypsinogen (Nature Genet (1996): 14:141-145). This paper reports sequence data of two independent families suffering from this disease. PCR amplificates from leukocyte or buccal swab DNA showed no mutation of exon 3 of cationic trypsinogen. Instead, in exon 2, an A-to-T tranversion was found that led to the substitution of Asn by Ile in the sixth amino acid of the active trypsin. In exons 4 and 5, silent mutations were found. In the other expressed trypsinogens, several homozygous alterations not associated to hereditary pancreatitis were identified. As a model of pathogenesis, we hypothesize that mutation of trypsinogen in exon 2 could lead to premature cleavage of the activation peptide of trypsinogen or to altered intracellular transport.

Hereditary pancreatitis and mutations of the cationic trypsinogen gene

BACKGROUND

Mutations of the cationic trypsinogen gene have been detected in hereditary pancreatitis. This article reviews current understanding of their function and clinical significance.

METHODS

An unrestricted Medline search was conducted using the key words hereditary pancreatitis and 'cationic trypsinogen . Additional material was obtained from references cited in original papers and recently published abstracts of meetings.

RESULTS AND CONCLUSION

Cationic trypsinogen mutations have been identified in most, but not all, families with hereditary pancreatitis. This confirms existing evidence that premature trypsinogen activation plays a central role in the pathogenesis of human pancreatitis. Patients currently clinically defined as having hereditary pancreatitis should be screened for the presence of cationic trypsinogen mutations. A subgroup of patients with non-hereditary pancreatitis may also benefit from being screened for these mutations. Patients with hereditary pancreatitis should be entered into prospective, multicentre trials investigating secondary screening for pancreatic cancer. Gene therapy for hereditary pancreatitis is beyond current technological capability but remains a future therapeutic prospect for this often debilitating condition.

Genetic predispositions to acute and chronic pancreatitis

Advances in molecular genetics have provided the powerful tools necessary to identify the key molecules and mechanisms that underly the disease process. Continued work in this area promises to reveal new insights as new disease genes are discovered. This article focuses on the insights into the cause of acute and chronic pancreatitis gained by investigation of the HP genes, the diagnosis of the known mutations, the fascinating observation of nonpenetrance, and a look at future directions.

Hereditary pancreatitis. Historical perspectives

Clinically, hereditary pancreatitis was not distinguishable from any other cause of pancreatitis. But astute clinical observations demonstrated an evolution toward chronic pancreatitis that could develop into carcinoma in some patients. A chromosomal abnormality was identified on chromosome 7q35, and then three separate genetic abnormalities were identified. It is now understood that a defect in trypsinogen is at the basis of the anomaly, and further developments should help identify new therapeutic approaches.

A major susceptibility locus influencing plasma triglyceride concentrations is located on chromosome 15q in Mexican Americans

Although several genetic forms of rare or syndromic hypertriglyceridemia have been reported, little is known about the specific chromosomal regions across the genome harboring susceptibility genes for common forms of hypertriglyceridemia. Therefore, we conducted a genomewide scan for susceptibility genes influencing plasma triglyceride (TG) levels in a Mexican American population. We used both phenotypic and genotypic data from 418 individuals distributed across 27 low-income, extended Mexican American families. For the analyses, TG values were log transformed (ln TG). We used a variance-components technique to conduct multipoint linkage analyses for localizing susceptibility genes that determine variation in TG levels. We used an approximately 10-15-cM map, which was made on the basis of information from 295 microsatellite markers. After accounting for the effects of sex and sex-specific age terms, we found significant evidence for linkage (LOD = 3.88) of ln TG levels to a genetic location between the markers GABRB3 and D15S165 on chromosome 15q. This putative locus explains 39.7+/-7% (P=.000012) of total phenotypic variation in ln TG levels. Suggestive evidence was found for linkage of ln TG levels to two different locations on chromosome 7, which are approximately 85 cM apart from each other. Also, there is some evidence for linkage of high-density lipoprotein cholesterol concentrations to a genetic location near one of the regions on chromosome 7. In conclusion, we found strong evidence for linkage of ln TG levels to a genetic location on chromosome 15q in a Mexican American population, which is prone to disease conditions such as type 2 diabetes and the insulin-resistance syndrome that are associated with hypertriglyceridemia. This putative locus appears to have a major influence on ln TG variation.