Polyvariant mutant CFTR genes in patients with chronic pancreatitis

IVS8-5T Allele of CFTR is the Risk Factor in Chronic Pancreatitis, Especially in Idiopathic Chronic Pancreatitis

BACKGROUND

Cystic fibrosis transmembrane conductance regulator IVS8-5T gene variation appears to be associated with a higher risk of chronic pancreatitis (CP); however, there is inconsistency between previous reported studies. Here, we performed a meta-analysis to investigate this relationship.

MATERIALS AND METHODS

PubMed and WANFANG databases were searched for the case-control studies that contained Patients with CP with IVS8-5T variation. Odd ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the relevance of IVS8-5T gene variation and CP.

RESULTS

Analysis showed that the frequency of the 5T allele was significantly higher in CP subjects than that in control subjects (OR = 1.43, 95% CI: 1.13-1.81, I² = 1.2%). Based on the subgroup analysis stratified by etiology, the 5T allele was associated with a higher risk of idiopathic chronic pancreatitis (ICP) (OR = 1.80, 95% CI: 1.18-2.76, I² = 0.0%) and not alcoholic CP (OR = 2.14, 95% CI: 0.98-4.66, I² = 0.0%). Further study indicated that the 5T allele was related to higher ICP prevalence in the European population (OR = 1.79, 95% CI: 1.06-3.03, I² = 0.0%). In contrast, there was no significant difference between ICP subjects and healthy controls within the Asian population (OR = 1.84, 95% CI: 0.91-3.72, I² = 38.0%).

CONCLUSIONS

Cystic fibrosis transmembrane conductance regulator IVS8-5T is a risk factor in patients with CP. IVS8-5T variation may play a significant role in the occurrence of ICP, especially in the European population.

CFTR: A New Horizon in the Pathomechanism and Treatment of Pancreatitis

Cystic fibrosis transmembrane conductance regulator (CFTR) is an ion channel that conducts chloride and bicarbonate ions across epithelial cell membranes. Mutations in the CFTR gene diminish the ion channel function and lead to impaired epithelial fluid transport in multiple organs such as the lung and the pancreas resulting in cystic fibrosis. Heterozygous carriers of CFTR mutations do not develop cystic fibrosis but exhibit increased risk for pancreatitis and associated pancreatic damage characterized by elevated mucus levels, fibrosis, and cyst formation. Importantly, recent studies demonstrated that pancreatitis causing insults, such as alcohol, smoking, or bile acids, strongly inhibit CFTR function. Furthermore, human studies showed reduced levels of CFTR expression and function in all forms of pancreatitis. These findings indicate that impairment of CFTR is critical in the development of pancreatitis; therefore, correcting CFTR function could be the first specific therapy in pancreatitis. In this review, we summarize recent advances in the field and discuss new possibilities for the treatment of pancreatitis.

Mechanisms of CFTR functional variants that impair regulated bicarbonate permeation and increase risk for pancreatitis but not for cystic fibrosis

CFTR is a dynamically regulated anion channel. Intracellular WNK1-SPAK activation causes CFTR to change permeability and conductance characteristics from a chloride-preferring to bicarbonate-preferring channel through unknown mechanisms. Two severe CFTR mutations (CFTRsev) cause complete loss of CFTR function and result in cystic fibrosis (CF), a severe genetic disorder affecting sweat glands, nasal sinuses, lungs, pancreas, liver, intestines, and male reproductive system. We hypothesize that those CFTR mutations that disrupt the WNK1-SPAK activation mechanisms cause a selective, bicarbonate defect in channel function (CFTRBD) affecting organs that utilize CFTR for bicarbonate secretion (e.g. the pancreas, nasal sinus, vas deferens) but do not cause typical CF. To understand the structural and functional requirements of the CFTR bicarbonate-preferring channel, we (a) screened 984 well-phenotyped pancreatitis cases for candidate CFTRBD mutations from among 81 previously described CFTR variants; (b) conducted electrophysiology studies on clones of variants found in pancreatitis but not CF; (c) computationally constructed a new, complete structural model of CFTR for molecular dynamics simulation of wild-type and mutant variants; and (d) tested the newly defined CFTRBD variants for disease in non-pancreas organs utilizing CFTR for bicarbonate secretion. Nine variants (CFTR R74Q, R75Q, R117H, R170H, L967S, L997F, D1152H, S1235R, and D1270N) not associated with typical CF were associated with pancreatitis (OR 1.5, p = 0.002). Clones expressed in HEK 293T cells had normal chloride but not bicarbonate permeability and conductance with WNK1-SPAK activation. Molecular dynamics simulations suggest physical restriction of the CFTR channel and altered dynamic channel regulation. Comparing pancreatitis patients and controls, CFTRBD increased risk for rhinosinusitis (OR 2.3, p<0.005) and male infertility (OR 395, p<<0.0001). WNK1-SPAK pathway-activated increases in CFTR bicarbonate permeability are altered by CFTRBD variants through multiple mechanisms. CFTRBD variants are associated with clinically significant disorders of the pancreas, sinuses, and male reproductive system.

Genetic risk for alcoholic chronic pancreatitis

In recent years many studies have examined the genetic predisposition to pancreatic diseases. Pancreatic disease of an alcoholic etiology was determined to be a multi-factorial disease, where environmental factors interact with the genetic profile of the individual. In this review we discuss the main results from studies examining the frequency of genetic mutations in alcoholic chronic pancreatitis.

Spectrum of mutations and variants/haplotypes of CFTR and genotype-phenotype correlation in idiopathic chronic pancreatitis and controls in Chinese by complete analysis

Mutations in cystic fibrosis transmembrane conductance regulator (CFTR) gene have been reported in patients with chronic pancreatitis. The authors examine whether the mutations and haplotypes of CFTR will increase the risk of developing idiopathic chronic pancreatitis (ICP) in Chinese and their genotype and phenotype correlations. Seventy-eight patients with ICP and 200 geographically and ethnically matched controls in Taiwan were analyzed. The entire 27 coding and intronic regions of the CFTR gene were identified using heteroduplex analytical techniques and confirmed by sequencing analysis. The presence of 125G/C, 1001+10C>T, IVSTn(TG)m, 1540A>G, c2694T>G, and c4521G>A were determined by directing sequencing. Abnormal CFTR allele was found to be thrice as frequent in ICP patients as in controls (22/156 vs 19/400, p < 0.0001). T5 allele was associated with early onset of ICP. In six-loci haplotype analysis, 13 common haplotypes were assembled in the 278 individuals tested. The 125G/1001+11C/TG12/470M/2694T/4521G haplotype was associated with risk of ICP (odds ratio 11.3; 95% confidence interval 2.3-54.6, p = 0.008) in Chinese. The mutation spectrum is different from other ethnic groups. A population-specific panel of CFTR changes should be recommended for targeted populations including ICP in Chinese. It is important to design suitable screening programs for different populations.

Prospective analysis of cystic fibrosis transmembrane regulator mutations in adults with bronchiectasis or pulmonary nontuberculous mycobacterial infection

BACKGROUND

Bronchiectasis and pulmonary infection with nontuberculous mycobacteria (NTM) may be associated with disease-causing mutations in the cystic fibrosis transmembrane regulator (CFTR).

METHODS

Fifty adult patients at Stanford University Medical Center with a diagnosis of bronchiectasis and/or pulmonary NTM infection were prospectively characterized by sweat chloride measurement, comprehensive mutational analysis of CFTR, and sputum culture results.

RESULTS

A de novo diagnosis of cystic fibrosis (CF) was established in 10 patients (20%). Patients with CF were more likely than those without CF to have mucus plugging seen on chest high-resolution CT, and women with a CF diagnosis were thinner, with a significantly lower mean body mass index than the non-CF subjects. Thirty CFTR mutations were identified in 24 patients (50% prevalence). Sweat chloride concentration was elevated > 60 mEq/dL (diagnostic of CF) in seven patients (14%), and from 40 to 60 mEq/dL in eight patients (16%). The frequency of CFTR mutations was elevated above that expected in the general population: heterozygous DeltaF508 (12% vs 3%), R75Q (14% vs 1%), and intron 8 5T (17% vs 5 to 10%). Other known CFTR mutations identified were V456A, G542X, R668C, I1027T, D1152, R1162L, W1282X, and L183I. Three novel CFTR mutations were identified: A394V, F650L, and C1344S.

CONCLUSIONS

Mutations in CFTR that alter RNA splicing and/or functional chloride conductance are common in this population, and are likely to contribute to the susceptibility and pathogenesis of adult bronchiectasis and pulmonary NTM infection. Careful clinical evaluation for disease cause should be undertaken in this clinical context.

Rapid and reliable genotyping of polymorphic loci modifying correct splicing of CFTR pre-mRNA using mass spectrometry

We describe a fast and unambiguous method for haplotyping the (TG)mTn repeat in IVS8 and determining three other single nucleotide polymorphisms (SNPs) in exons 10, 14a and 24 in the cystic fibrosis transmembrane conductance regulator (CFTR) gene affecting correct splicing of the CFTR pre-mRNA using primer extension and mass spectrometry. The diagnostic products are generated by primer extension (PEX) reactions, which require a single detection primer complementary to a region downstream of a target strand's variable site. On addition of a polymerase and an appropriate mixture of dNTP's and 2', 3'-dideoxynucleotide triphosphates (ddNTP's), the primer is extended through the mutation region until the first ddNTP is incorporated and the mass of the extension products determines the composition of the variable site. Analysis of patient DNA assigned the correct and unambiguous haplotype for the (TG)mTn repeat in intron 8 of the CFTR gene. Additional crucial SNPs influencing correct splicing in exon 10, 14 and 24 can easily be detected by biplexing the assay to genotype allelic variants important for correct splicing of the CFTR pre-mRNA. Different PEX reactions with subsequent mass spectrometry generate sufficient data, to enable unambiguous and easy haplotyping of the (TG)mTn repeat in the CFTR gene. The method can be easily extended to the inclusion of additional SNPs of interest by biplexing some of the PEX reactions. All experimental steps required for PEX are amenable to the high degree of automation desirable for a high-throughput diagnostic setting, facilitating the work of clinicians involved in the diagnosis of non-classic cystic fibrosis.

ERCP findings in idiopathic pancreatitis: patients who are cystic fibrosis gene positive and negative

BACKGROUND

Our series of patients with idiopathic pancreatitis (IP) found a cystic fibrosis (CF) gene abnormality in 19% compared with 3.5% in patients without pancreatitis.

OBJECTIVE

The objective was to determine whether the CF gene predicts more severe ERP findings.

DESIGN

This was a retrospective case-control study.

SETTING AND PATIENTS

From July 1998 to August 2004, CF gene analysis was performed in 819 patients with IP via Genzyme Genetics. The panel tests for 70 to 87 alleles and has a detection rate of more than 90% of the cases. Sixty-nine patients (8.4%) who had at least one CF gene positive mutation were the study cohort. A total of 218 patients with IP and negative CF gene mutation were randomly selected from our database to be in the control group.

MAIN OUTCOME MEASUREMENTS

Pancreatograms were evaluated for chronic pancreatitis (CP) based on Cambridge criteria. The results of the gene analysis were not available at the time of pancreatogram interpretation.

RESULTS

Among patients positive for the CF gene, 42 (61%) were women. The mean age at intervention was 40 years (range 14-80 years), and 48 patients (70%) had cholecystectomy. Among patients who were negative for the CF gene, 147 (67%) were women. The mean age at intervention was 41 years (range 9-89 years), and 125 patients (57%) had cholecystectomy. Compared with controls, cases had higher incidence of CP (62% vs. 48%, p = 0.05), grade III CP (35% vs. 18%, p = 0.004), pseudocysts (12% vs. 4%, p = 0.036) and pancreatic strictures (20% vs. 8%, p = 0.008).

LIMITATIONS

The limitations of the study were (1) retrospective design and (2) the panel used tests only for 70 to 87 alleles (of approximately, 900 CF transmembrane conductance regulator genes known).

CONCLUSIONS

The mean age at intervention in both groups was similar. CP, grade III CP, pseudocysts, and pancreatic strictures were more common among patients who were CF gene positive.

The cystic fibrosis transmembrane conductance regulator gene and ion channel function in patients with idiopathic pancreatitis

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations are associated with cystic fibrosis (CF)-related monosymptomatic conditions, including idiopathic pancreatitis. We evaluated prospectively enrolled patients who had idiopathic recurrent acute pancreatitis or idiopathic chronic pancreatitis, healthy controls, CF heterozygotes, and CF patients (pancreatic insufficient or sufficient) for evidence of CFTR gene mutations and abnormalities of ion transport by sweat chloride and nasal potential difference testing. DNA samples from anonymous blood donors were controls for genotyping. At least one CFTR mutation or variant was carried in 18 of 40 patients (45%) with idiopathic chronic pancreatitis and in 6 of 16 patients (38%) with idiopathic recurrent acute pancreatitis but in only 11 of the 50 controls (22%, P=0.005). Most identified mutations were rare and would not be identified in routine genetic screening. CFTR mutations were identified on both alleles in six patient (11%). Ion transport measurements in patients with pancreatitis showed a wide range of results, from the values in patients with classically diagnosed CF to those in the obligate heterozygotes and healthy controls. In general, ion channel measurements correlated with the number and severity of CFTR mutations. Twelve of 56 patients with pancreatitis (21%) fulfilled current clinical criteria for the diagnosis of CF, but CFTR genotyping alone confirmed the diagnosis in only two of these patients. We concluded that extensive genotyping and ion channel testing are useful to confirm or exclude the diagnosis of CF in the majority of patients with idiopathic pancreatitis.

Variations of the CFTR gene in the Hanoi-Vietnamese

In order to investigate polymorphic backgrounds of the cystic fibrosis transmembrane conductance regulator gene (CFTR) in the Vietnamese, we analyzed 495 blood samples of randomly selected healthy individuals in Hanoi for the delta F508 mutation and TG-repeats, poly-T, and M470V polymorphisms. We compared their distributions with those of Caucasians and other Asian populations. No delta F508 mutation was found, being consistent with the extremely low incidence of cystic fibrosis (CF) in Vietnam. Allele frequency of the T5 allele promoting exon 9 skipping was 0.037. Greater number of TG-repeats, which is known to facilitate this aberrant splicing, was a predominant trend in the Vietnamese and other Asians. A "T5-TG12-V470" haplotype was most common (29/37) among T5-bearing haplotypes. Three major haplotypes, T7-TG12-M470, T7-TG11-V470, and T7-TG12-V470, estimated by PHASE program, related to 92% of the population. This is the first study of the CFTR gene among the Vietnamese.

The impact of cystic fibrosis and PSTI/SPINK1 gene mutations on susceptibility to chronic pancreatitis

This article reviews current concepts regarding the pathobiology of cystic fibrosis pancreatic disease. It summarizes recent studies on the relationship between CFTR mutations and pancreatitis, and it reviews several unresolved issues in the field.

Reduced CFTR function and the pathobiology of idiopathic pancreatitis

Idiopathic chronic pancreatitis (ICP) is the leading cause of chronic pancreatitis in children and nonalcoholic adults. The risk of developing ICP is increased in individuals who have mutations of the cystic fibrosis gene (CFTR) and of a trypsin inhibitor gene (PSTI). In studies from the United States and France, the risk of ICP is increased about 40-fold by having two abnormal copies of the CFTR gene, about 14-fold by having the N34S PSTI mutation, and about 500-fold by having both. When ICP patients have two abnormal copies of the CFTR gene, there is also evidence of reduced residual CFTR protein function in extrapancreatic tissues based on clinical findings and nasal ion transport responses. Thus, pancreatitis risk is highest in individuals who have abnormalities in both the pancreatic ducts (CFTR) and acini (PSTI). These findings indicate that PSTI is a modifier gene for CFTR-related ICP and have implications for the diagnosis and pathogenesis of pancreatitis.

Relapsing pancreatitis due to a novel compound heterozygosity in the CFTR gene involving the second most common mutation in central and eastern Europe [CFTRdele2,3(21 kb)]

A 43-year-old otherwise healthy female patient presented with mild pancreatitis. Her family history revealed that her only son had cystic fibrosis. Genotyping of the patient demonstrated CFTR compound heterozygosity CFTRdele2,3(21 kb) and R117H and wild type alleles of the poly-T-tract in intron 8 (7T/7T). No mutations were detected in the cationic pancreatic trypsinogen (PRSS1) and the pancreatic secretory trypsinogen inhibitor (SPINK1) genes. CFTRdele2,3(21 kb) has only been described in 2000 and is the second most frequent severe CFTR mutation after DeltaF508 in central and eastern Europe. This haplotype should be included in the genetic panel when evaluating patients of central or eastern European genetic background for possible CFTR related pancreatitis.

High frequency of (TG)mTn variant tracts in the cystic fibrosis transmembrane conductance regulator gene in men with high semen viscosity

OBJECTIVE

To evaluate a possible correlation between abnormal semen consistency and cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations and variant tracts.

DESIGN

Study of CFTR mutations and variant tracts in men with high semen viscosity as compared with normospermic men.

SETTING

University-based centers for andrology, clinical biochemistry, and cystic fibrosis.

PATIENT(S)

Forty-six male partners from infertile couples with sine causa high semen viscosity compared with 72 normospermic men.

INTERVENTION(S)

Semen sample collection.

MAIN OUTCOME MEASURE(S)

We obtained the (TG)mTn polymorphic tracts and a panel of 31 mutations of CFTR, semen viscosity, and semen variables.

RESULT(S)

The frequencies of the (TG)12 and T5 variant alleles were statistically significantly higher in men with high semen viscosity (17.4% and 7.6%, respectively) than in the normospermic control group (6.9% and 1.4%, respectively). The frequency of the genotypes carrying (TG)12 or T5 was statistically significantly higher in men with high semen viscosity (39.1%) than in the normospermic control group (16.7%). Four men with high semen viscosity showed the variant (TG)12T5 haplotype; one of these men presented variant tracts on both alleles. None of the normospermic controls showed a (TG)12T5 haplotype.

CONCLUSION(S)

Semen hyperviscosity could be considered a "minimal clinical expression" of cystic fibrosis; CFTR gene sequence variations may constitute the genetic basis for this disease.

Homozygous (TG)11 allele in intron 8 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene has a protective role against bicarbonate decrease in pure pancreatic juice among Japanese male alcoholics

BACKGROUND

Heavy drinkers have a high incidence of chronic pancreatitis (CP), but the mechanism of alcohol-related CP is largely unknown. Exocrine pancreatic insufficiency exists in about 90% of the patients with cystic fibrosis (CF), which results from an abnormal cystic fibrosis transmembrane conductance regulator gene (CFTR).

AIM

To investigate in Japanese alcoholics the association between bicarbonate concentration in pure pancreatic juice and one of the polymorphisms of the CFTR gene, the (TG)m Tn tract length in intron 8.

METHODS

Fifty-six patients under treatment for alcohol dependence were stimulated by intravenous injection of secretin during endoscopic retrograde cholangiopancreatography to provide pancreatic juice specimens. Individual maximum bicarbonate concentrations (MBC) were compared with (TG)m Tn tract polymorphisms identified by directly sequencing lymphocyte DNA.

RESULTS

Among the 41 patients able to provide adequate pancreatic juice specimens, 15 had low MBC and 26 had normal MBC. The frequencies of the six haplotypes identified in these patients were 17.1% (TG)11T7/(TG)llT7, 46.3% (TG)11T7/(TG)12T7, 29.3% (TG)12T7/(TG)12T7, 2.4% (TG)10T9/(TG)11T7, 2.4% (TG)12T5/(TG)11T7, and 2.4% (TG)12T6/(TG)12T7. Among the 92.7% of patients who had the common (TG) miT7/(TG)m2T7 haplotype, all of the 7 with homozygous (TG)11 alleles had normal MBC (p<0.05).

CONCLUSION

Alcoholics with homozygous (TG)11 alleles in intron 8 of the CFTR gene appear to be protected against decreased MBC, compared with those who have the (TG)11/(TG)12 and (TG)12/(TG)12 genotypes, suggesting a role for CFTR gene polymorphism in the progression of alcohol-related pancreatic disease.

The role of cystic fibrosis gene mutations in determining susceptibility to chronic pancreatitis

This article reviews current concepts regarding the pathobiology of cystic fibrosis pancreatic disease. It summarizes recent studies on the relationship between CFTR mutations and pancreatitis, and it reviews several unresolved issues in the field.

Pancreatitis in hispanic patients with cystic fibrosis carrying the R334W mutation

BACKGROUND & AIMS

Cystic fibrosis (CF) results from abnormal production of sticky mucus, which obstructs many organs. In most cases, the pancreas is severely compromised, but 10%-15% of patients with CF have pancreas sufficiency (PS) and are subject to develop pancreatitis. The aim of this study is to determine which specific genotypes lead to the development of pancreatitis in patients with CF.

METHODS

We used prospective data collected by the Cystic Fibrosis Foundation and performed a nested case-control study with all patients who reported at least 1 episode of pancreatitis constituting the cases. We used logistic regression to assess the association between pancreatitis and genotype and the Kaplan-Meier method to estimate the cumulative incidence of pancreatitis for selected genotypes.

RESULTS

Three hundred sixty-four of 17,871 genotyped patients with CF (2.0%) reported at least 1 episode of pancreatitis. Only 0.9% of 12,997 patients with genotypes generally associated with pancreas insufficiency reported pancreatitis against 11.9% of 868 patients carrying at least 1 mild CF mutation generally associated with PS. The greatest rate of pancreatitis (19.0%) was observed for patients carrying an R334W mutation: 48% of these 79 patients were Hispanic and 13 patients were living in Puerto Rico.

CONCLUSIONS

Of all patients with CF, those carrying an R334W mutation have the greatest risk for developing pancreatitis. This mutation is found mostly in Hispanic patients with CF living in Puerto Rico. There are no current data to determine whether asymptomatic carriers of the R334W mutation are at greater risk for developing pancreatitis or whether this mutation is frequent in Hispanics with idiopathic pancreatitis.

Mutations of the CFTR gene in pancreatic disease

INTRODUCTION

An association has been found between CFTR gene mutations and chronic pancreatitis; however, there is a lack of information about the frequency of CFTR gene mutations in acute pancreatitis and in pancreatic cancer.

AIM

To prospectively evaluate the prevalence of CFTR gene mutations in acute pancreatitis, chronic pancreatitis, and pancreatic cancer.

METHODOLOGY

Ninety-eight consecutive patients were studied and divided into 3 groups: 34 patients with acute pancreatitis, 46 patients with chronic pancreatitis, and 18 patients with pancreatic cancer. The mutation analysis of the CFTR gene was carried out using diagnostic commercial kits for the simultaneous detection of 29 mutations and Tn polymorphism.

RESULTS

Among the 98 patients studied, 12 (12.2%) had CFTR gene mutations: 2 of the 34 patients (5.9%) with acute pancreatitis, 9 of the 46 (19.6%) with chronic pancreatitis, and 1 of the 18 (5.6%) with pancreatic cancer. All the mutations were found in heterozygosis (2 DeltaF508, 1 W1282X, and 9 T5 allele).

CONCLUSION

Our prospective study adds further information about the frequency of CFTR mutations in patients with a single episode of acute pancreatitis. Furthermore, our results suggest an association of CFTR gene mutations with chronic alcoholic pancreatitis and emphasize the need for a multicenter study, possibly multinational, to conclusively establish the role of CFTR mutations as a genetic susceptibility factor for this disease.

Cystic fibrosis transmembrane conductance regulator (CFTR) gene defects in patients with primary sclerosing cholangitis

BACKGROUND/AIMS

Because biliary tract lesions that resemble those of primary sclerosing cholangitis (PSC) may occur in cystic fibrosis (CF), we examined the prevalence and influence of CF transmembrane conductance regulator (CFTR) gene mutations in PSC patients.

METHODS

Genomic DNA was analyzed in 29 consecutive PSC patients and in 115 healthy control individuals. A scanning method followed by direct DNA sequencing was used to scan the CFTR coding regions.

RESULTS

Four patients (13.8%) were heterozygous for a CFTR mutation, including a new putative severe CF-causing mutation (N782K), and three mild defects (L997F, D1270N, and S1235R). The comparison of PSC patients with healthy controls showed no significant difference in the frequency of CFTR mutations (P=0.415). In addition, two patients (6.9%) were heterozygous for the IVS8-5T allele, which is not significantly different from the 5-6%-prevalence in the general population. Unusual clinical features including a severe outcome in childhood, with a lethal outcome at age 22, and biliary aspergillosis were recorded in patients with a CFTR mutation.

CONCLUSIONS

The proportion of CF carriers is not significantly higher in PSC patients than in the general population. The possibility that CFTR mutations may contribute to a severe clinical course in PSC patients is worth further examining.

Cystic fibrosis and related diseases of the pancreas

The discovery of the gene for cystic fibrosis (CF), the cystic fibrosis transmembrane conductance regulator (CFTR), brought about a new era in the study of this disease. Identification of the molecular target has yielded a flood of data that add to our understanding of the pathogenesis, diagnosis and treatment of CF. The CFTR protein is a cAMP-regulated Cl(-) channel with multiple functions in epithelial cells. In the exocrine pancreas the CFTR plays a key role in the apical Cl(-), HCO(3)(-), and water transport in duct cells. The severe loss of functions, caused by mutations of the CFTR gene, leads to pathological lesions of the pancreas. Over 1200 CFTR mutations and polymorphisms have been identified and their diversity may explain the high level of heterogeneity in the CF phenotype. Mutation analyses of the CFTR gene have revealed a spectrum of CFTR-related diseases that do not fit the classical CF picture but are associated with dysfunction of CFTR, such as chronic pancreatitis.

Determination of the relative contribution of three genes-the cystic fibrosis transmembrane conductance regulator gene, the cationic trypsinogen gene, and the pancreatic secretory trypsin inhibitor gene-to the etiology of idiopathic chronic pancreatitis

In the last 5 years, mutations in three genes, the cystic fibrosis transmembrane conductance regulator (CFTR) gene, the cationic trypsinogen (PRSS1) gene, and the pancreatic secretory trypsin inhibitor (PSTI) gene, have been found to be associated with chronic pancreatitis (CP). In this study, using established mutation screening methods, we systematically analysed the entire coding sequences and all exon/intron junctions of the three genes in 39 patients with idiopathic CP (ICP), with a view to evaluating the relative contribution of each gene to the aetiology of the disease. Our results demonstrate that, firstly, 'gain-of-function' mutations in the PRSS1 gene may occasionally be found in an obvious ICP subject. Secondly, presumably 'loss-of-function' mutations in the PSTI gene appear to be frequent, with a detection rate of at least 10% in ICP and, finally, abnormal CFTR alleles are common: at least 20% of patients carried one of the most common CFTR mutations, and about 10% of patients were compound heterozygotes, having at least one 'mild' allele. Thus, in total, about 30% of ICP patients carried at least one abnormal allele in one of the three genes, and this is the most conservative estimate. Moreover, a trans-heterozygous state with sequence variations in the PSTI/CFTR genes was found in three patients. However, an association between the 5T allele in intron 8 of the CFTR gene and ICP remains unproven.

Cystic fibrosis gene mutations and pancreatitis risk: relation to epithelial ion transport and trypsin inhibitor gene mutations

BACKGROUND & AIMS

Nonalcoholic chronic pancreatitis is usually idiopathic and often associated with cystic fibrosis gene (CFTR) mutations. It is unknown whether pancreatitis risk correlates with having 1 or 2 CFTR mutations, abnormal epithelial ion transport, or mutations of other genes.

METHODS

We tested 39 patients with idiopathic chronic pancreatitis (mean age at diagnosis, 33 years) for common mutations of CFTR and of genes encoding a trypsin inhibitor (PSTI) and trypsinogen (PRSS1). To exclude hereditary pancreatitis, we initially relied on family history and subsequently tested for PRSS1 mutations. Twenty subjects were tested for rare CFTR mutations (DNA sequencing) and 11 were tested for extrapancreatic CFTR function (clinical and physiologic evaluation).

RESULTS

Mutations were identified in 24 of 39 subjects. Nine patients had cystic fibrosis-causing mutations, 8 of whom also had mild-variable mutations. Eight others had only mild-variable mutations. Nine subjects had the N34S PSTI mutation and 1 had hereditary pancreatitis (R122H, PRSS1). Pancreatitis risk was increased approximately 40-fold by having 2 CFTR mutations (P < 0.0001), 20-fold by having N34S (P < 0.0001), and 900-fold by having both (P < 0.0001). Subjects with 2 CFTR mutations had abnormal nasal epithelial ion transport and clinical findings suggesting residual CFTR function between that in cystic fibrosis and in carriers. By contrast, subjects with only PSTI mutations had normal CFTR function.

CONCLUSIONS

CFTR-related pancreatitis risk correlates with having 2 CFTR mutations and reduced extrapancreatic CFTR function. The N34S PSTI mutation increased risk separately. Testing for pancreatitis-associated CFTR and PSTI genotypes may be useful in nonalcoholic pancreatitis.

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.