Genetic Testing in Chronic Pancreatitis and Pancreatic Cancer -- Can You Use it in Patient Care?

[Guest guest]

Genetic Testing in Chronic Pancreatitis and Pancreatic Cancer -- Can You

Use it in Patient Care?

Michele D. Bishop, M.D., MMSc

Michele D. Bishop, M.D., MMSc is an Assistant Professor, Mayo Medical

School, Gastroenterology and Hepatology, Mayo Clinic ville

Introduction

Genetic mutations contribute to a wide range of pancreatic disorders.

Three areas of genetic mutations associated with recurrent acute and chronic

pancreatitis will be presented: Cystic fibrosis, which is linked to CFTR gene

mutations, and Hereditary Pancreatitis which is linked to PRSS1 and SPINK1

(PRSI) gene mutations. Approximately 5% of pancreatic cancers have a hereditary

origin as well, and a gene for this was identified recently. Indications for and

implications of genetic testing will be discussed.

Cystic Fibrosis (CFTR) Mutations

Classic Cystic Fibrosis

Cystic fibrosis (CF) is by far the most common inherited cause of exocrine

pancreatic disease in childhood. It is the most common autosomal recessive

life-shortening disorder in Caucasians with an incidence between 1:2000 and

1:3000 live births.1 Identification of the cystic fibrosis gene on the long arm

of chromosome 7 in 1989 led to the elucidation of its protein product, the

cystic fibrosis transmembrane conductance regulator (CFTR), a cyclic-AMP

mediated chloride channel.2 Over 1000 mutations of the gene have been described

to date.3 Mutations in the CFTR gene lead to chloride channel dysfunction and

impaired ion transport across epithelial cell membranes. In the pancreas, this

results in impairment of bicarbonate and chloride secretion, reduced fluid flow

in pancreatic ducts and protein hyperconcentration with inspissation. A

classification system for mutations is comprised of five classes based on

chloride channel function4, with Classes I, II, and III mutations conferring

complete loss of CFTR function and severe disease. Class IV and V mutations

retain some CFTR function leading to milder phenotypes. Eighty-five percent of

children diagnosed with the " classic " form of CF have two Class I, II or II

mutations and these children have pancreatic insufficiency. These patients

develop severe pulmonary disease, the males are infertile and average life

expectancy is approximately 30 years. Patients with at least one Class IV or V

mutation are pancreatic sufficient, do not have steatorrhea and do not require

pancreatic enzyme supplementation. Pancreatic sufficient patients are diagnosed

at a later age, experience normal growth during childhood and have a better

overall prognosis than their pancreatic insufficient counterparts. Pancreatitis

is not an uncommon finding in pancreatic sufficient CF patients5, and in fact

may be the sole presenting symptom of CF.6

CFTR Mutations in Recurrent Acute and Chronic Pancreatitis

Four published studies have reported that CFTR gene mutations are present

in patients with idiopathic pancreatitis.7-10 Most of these patients had

mutations on only one allele and no significant pulmonary or other

characteristic CF findings were present. It would be expected that patients with

isolated pancreatitis, in the absence of other clinical manifestations of CF,

would carry the milder Class IV or V mutations on at least one allele. At this

time, most of these mild mutations are not included in standard commercially

available panels used for screening for Cystic Fibrosis. Therefore, to study

each of these patients the complete DNA sequencing of the CFTR gene is required

to look for the more than 1000 known mutations in CFTR. When full DNA sequencing

has been performed, up to 60% of patients had at least one mutation.10, 11 A

considerable number of compound heterozygotes were also identified. There are

individual patients with two mutations, one severe and one mild.

Finding a CFTR mutation in a patient with idiopathic pancreatitis does not

infer that the patient has cystic fibrosis. A consensus statement by the CF

Foundation has determined that the diagnosis of CF requires the following two

criteria: i) phenotypic features characteristic of CF, a history of CF in a

sibling, or a positive newborn screening test, and ii) elevated sweat chloride

concentration, two proven disease-causing CFTR mutations, or in vivo

demonstration of abnormal ion transport across respiratory epithelium

characteristic of CF.12

Characteristic CF phenotype features include pancreatic insufficiency and

recurrent pancreatitis. However, the majority of idiopathic pancreatitis

patients do not meet criteria for CF. Instead, most fall somewhere on a

continuum between normal and classic CF. Male patients with isolated infertility

due to congenital bilateral absence of the vas deferens and CFTR mutations also

fall on this continuum between normal and CF.13 It appears likely that in the

next few years many diseases will be found to be the result of abnormal ion

secretion across epithelial cells are due to CFTR gene abnormalities.

Undoubtedly, other factors influence disease activity such as modifier genes and

environmental exposures. Perhaps underlying mutations in CFTR predispose some

patients to pancreatitis when exposed to certain environmental toxins, such as

" social " alcohol use, or when paired with other abnormal genes not yet

identified.

Genetic testing for any disease, especially ones under current

investigation, must be approached with caution. There are many possible

implications of genetic testing in CF, including issues regarding heredity and

insurance, that should be discussed with patients prior to testing. Patients

should learn that the results of any testing might be difficult to interpret at

this preliminary stage of research. The implications for family members may also

be impossible to predict. As there is no specific treatment for CF- related

pancreatitis, the treatment for all etiologies of chronic pancreatitis is the

same. More complete genetic tests are anticipated in the near future, but at

this time, the most comprehensive test available for commercial use only tests

for 86 of the more than 1000 known mutations. Patients may be given incomplete

data if this test is used, as a negative result by no means " rules out " CF

related pancreatitis. Sweat tests are more widely available, inexpensive, and

safe. A confirmed positive sweat test, in the setting of recurrent pancreatitis

or pancreatic insufficiency meets the criteria for classic CF. Most patients

with at least one mild mutation, however, have normal or borderline sweat tests.

Therefore, it is recommended that patients only undergo genetic testing as part

of a research study, and that they meet with a professional genetics counselor

prior to agreeing to be tested.

Hereditary Pancreatitis (PRSS1) Mutations

Hereditary pancreatitis was first described by Comfort and Steinberg in

1952.14 It is an autosomal dominant disease with variable expression, and an

estimated penetrance of 80%.15 Mutations in the cationic trypsinogen gene

(PRSS1) are thought to cause the disease, which was mapped to chromosome 7q35 in

1996 by Whitcomb and colleagues.15 Hereditary pancreatitis is characterized by

recurrent attacks of acute pancreatitis starting in childhood or adolescence,

with frequent progression to chronic pancreatitis. The majority of families are

of white European ancestry, but cases have been reported in Japan, India and

other ethnic groups. Several mutations have been described, but two, R122H and

N29I, are confirmed to be associated with disease.16 Mutations in the cationic

trypsinogen gene are thought to cause pancreatitis by the absence of a cleavage

site for inactivation of trypsin, thus permitting increased trypsin activity in

the pancreatic parenchyma and autodigestion.16

Patients with hereditary pancreatitis also have an increased risk for

pancreatic adenocarcinoma.17 The mean age at diagnosis of cancer is 54 years,

with a mean interval of 40 years from development of symptoms of pancreatitis to

diagnosis of cancer. The estimated cumulative risk of pancreatic cancer to age

70 years is approximately 40%. Smoking appears to double the already high risk

of pancreatic cancer in these patients, and lowers the age of onset by

approximately 20 years.17

Unfortunately, there is no effective screening test for the early

detection of pancreatic cancer in these high risk individuals, and no guidelines

are available for the management of patients considered to be at high risk to

develop pancreatic cancer. It is recommended that these individuals be managed

in clinical trials which are hoping to find early diagnostic tests.

Gene therapy for hereditary pancreatitis is " beyond current technology " .16

However, testing for PRSS1 mutations is now widely available commercially. A

consensus statement was recently published with guidelines for indications,

counseling and patient informed consent issues.18 In brief, genetic testing is

recommended for families where there is a history of idiopathic recurrent acute

pancreatitis or of idiopathic chronic pancreatitis.

Trypsin Inhibitor (SPINK1) Mutations

In June, 2000, Witt and colleagues reported that mutations in the serine

protease inhibitor, Kazal type 1 (SPINK1 or PSTI gene), are associated with

recurrent acute pancreatitis.19 Ninety-six unrelated German or Austrian children

and adolescents were studied. 71% had idiopathic disease and 29% had a family

history of pancreatitis. Direct DNA sequencing of the intrapancreatic trypsin

inhibitor, SPINK1, identified mutations in 23% of patients. Six patients were

homozygous for the missense mutation, N34S. In comparison, only one of 279

healthy control subjects in this study was found to carry the mutation. Genetic

testing is not available outside of a research study at this time.

Hereditary Pancreatic Cancer

In 1999, it was estimated that 28,600 new cases of pancreatic cancer in

the US would be diagnosed, and the total number of deaths due to pancreatic

cancer was projected to be 28,600.20 Approximately 5% of pancreatic cancers have

a hereditary association. Genetic disorders predisposing to pancreatic cancer

can be found in Table 1.

Table 1

Genetic disorders associated

with pancreatic cancer:

Familial pancreatic adenocarcinoma seems to have an autosomal

dominant pattern of inheritance. Some families report cancer in multiple

generations and others in multiple siblings. There is currently no standard

definition of familial pancreatic cancer. It has been described as pancreatic

cancer with at least one first-degree relative with pancreatic cancer.21 In

April 2002, Eberle reported the localization of the gene for familial pancreatic

cancer on the long arm of chromosome 4.22 They performed DNA analysis on a

family from the Seattle area with 20 affected family members (five out of six

brothers affected). At this time, a genetic test is not available for family

members of pancreatic cancer patients, but this may be an option in the near

future. Finding a genetic mutation would prompt the need for screening.

a.. Hereditary pancreatitis

b.. FPC (Familial Pancreatic Cancer)

c.. FAMMM syndrome (Familial Atypical Multiple Mole Melanoma)

d.. Lynch syndrome II

e.. Hereditary breast cancer (BRCA2)

f.. Ataxia telangiectasia

g.. MEN1 (Pituitary, parathyroid and pancreas)

h.. HNPCC (Hereditary Non-Polyposis Colon Cancer)

i.. FAP (Familial Adenomatous Polyposis)

j.. Peutz-Jeghers Syndrome

k.. Cystic fibrosis (case reports)

The ideal goal of screening family members at risk is to diagnose them

before the development of cancer, when they have dysplasia or carcinoma-in-situ,

and to perform surgery. There is no standard recommended screening regimen to

identify pancreatic dysplasia, but Brentnall, has reported dysplastic lesions

detected by endoscopic ultrasound. 23 This remains to be confirmed by other

investigators.

Summary Concepts

1.. CFTR gene mutations have been identified in a significant number of

adult patients with idiopathic recurrent acute and chronic pancreatitis, without

classic findings of cystic fibrosis.

2.. Hereditary pancreatitis is caused by mutations in the cationic

trypsinogen gene (PRSS1) in an autosomal dominant pattern, and carries a

significantly increased risk of pancreatic cancer.

3.. Mutations in the gene encoding the serine protease inhibitor, Kazal

type 1, a pancreatic trypsin inhibitor (SPINK1), have been identified in young

patients with recurrent acute pancreatitis.

4.. Approximately 5% of pancreatic cancers have a hereditary origin.

5.. Genetic testing outside of an ethics committee-approved research

protocol is only recommended for Hereditary Pancreatitis (PRSS1) mutations at

this time.

References

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database. Cystic Fibrosis Genetic Analysis Consortium 2001.

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ville Medicine / June/July, 2002

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Mark E. Armstrong

www.top5plus5.com

NW Chapter Rep

Pancreatitis Association, International