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Genetics

To date (Spring 2018) there has not been any specific genetics identified as the sole cause of EPI, however, the consensus among EPI veterinarian researchers is that, until further research yields more in-depth answers, EPI is most likely a combination of genetics and environmental causes.  Below are 3 different studies:

2 Studies by Dr. Leigh Anne Clark 

 

JUNE 2015ANIMAL GENETICS PUBLICATION
 

Association of DLA-DQB1 alleles with exocrine pancreatic insufficiency in Pembroke  Welsh Corgis

  1. J. M. Evans1
  2. K. L. Tsai1
  3. A. N. Starr-Moss1
  4. J. M. Steiner2 and
  5. L. A. Clark1,*

Article first published online: 19 JUN 2015

 
DOI: 10.1111/age.12317 
 
Exocrine pancreatic insufficiency (EPI) is a digestive disorder resulting from the insufficient secretion of enzymes from the pancreas. In dogs, this condition is often attributed to pancreatic acinar atrophy, wherein the enzyme-producing acinar cells are believed to be destroyed through an autoimmune process. Although EPI affects many diverse breeds, to date, molecular studies have been limited to the German Shepherd dog. A recent study of major histocompatibility genes in diseased and healthy German Shepherd dogs identified both risk and protective haplotypes. Herein, we genotyped DLA-DQB1 in Pembroke Welsh Corgis to determine whether dog leukocyte antigen alleles contribute to the pathogenesis of EPI across dog breeds. We evaluated 14 affected and 43 control Pembroke Welsh Corgis, which were selected based on an age of onset similar to German Shepherd dogs. We identified one protective allele (odds ratio = 0.13, P-value = 0.044) and one risk allele (odds ratio = 3.8, P-value = 0.047). As in German Shepherd dogs, the risk allele is a duplication of DLA-DQB1 (alleles DQB1*013:03 and 017:01); however, Pembroke Welsh Corgis have acquired a single polymorphism on DQB1*017:01. Thus, the DLA-DQB1 duplication is a risk allele for EPI in at least two breeds. 

 

1 Study by Dr. Elias Westermarck 2010

Brief Communication – J Vet Intern Med 2010;24:450–452
Heritability of Exocrine Pancreatic Insufficiency in
German Shepherd Dogs

E. Westermarck, S.A.M. Saari, and M.E. Wiberg

Brief Communication – J Vet Intern Med 2010;24:450–452
Heritability of Exocrine Pancreatic Insufficiency in
German Shepherd Dogs

E. Westermarck, S.A.M. Saari, and M.E. Wiberg

Background: Several studies have revealed that exocrine pancreatic insufficiency (EPI) is an inherited disease in German
Shepherd Dogs (GSDs). Pedigree analyses have suggested an autosomal recessive inheritance model.
Objective: Test mating of 2 dogs with EPI.
Animals: A sire and dam purebred GSD both with EPI and a litter of 6 puppies.
Methods: Test mating and long-term follow-up of offspring. The pancreas was biopsied via laparotomy on 26 occasions.
Serum trypsin-like immunoreactivity was measured. Study was approved by Animal Ethics Committee.
Results: During the 12-year study period only 2 of the 6 offsprings developed pancreatic acinar atrophy (PAA). In 1 puppy,
end-stage PAA and in the other puppy partial PAA was diagnosed.
Conclusions and Clinical Importance: PAA is not a congenital disease in GSDs. This study provided evidence that PAA is
not inherited in a simple autosomal recessive fashion.
Key words: Biopsy; Pancreatic acinar atrophy; Polygenic inheritance; Test mating; Trypsin-like immunoreactivity.

Abbreviations:
EM electron microscopy
EPI exocrine pancreatic insufficiency
GSD German Shepherd Dog
PAA pancreatic acinar atrophy
TLI trypsin-like immunoreactivity

     Canine exocrine pancreatic insufficiency (EPI) is a disease characterized by inadequate production of digestive enzymes by pancreatic acinar cells. Affected dogs typically show such clinical signs as polyphagia, weight loss, yellowish poorly digested loose and pulpy feces, increased fecal volume, and frequent defecation.1. EPI has been reported in many breeds, but it is most commonly seen in German Shepherd Dogs (GSDs). In GSDs, the underlying cause of EPI is pancreatic acinar
atrophy (PAA). A characteristic of PAA is selective destruction of the digestive enzyme producing acinar cells.1, PAA has features of autoimmune disease, including genetic suspectibility to disease. 1.2. 
     
Several studies have indicated that EPI is an inherited disease in GSDs, and most research of the inheritance model by pedigree analysis suggests that EPI is inherited in an autosomal recessive fashion.3–5 The prevalence of affected dogs in most reports has, however, been lower (!15%) than expected 25% for a simple autosomal recessive trait; thus, a polygenic mode of inheritance has been proposed.4 The mutation or candidate gene has not been identified.6.

Materials and Methods
     This study was performed during 1987 to 2000. Both parents were purebred GSDs (dam 4 years, sire 6 years), with different progenitors. EPI diagnosis for both parents was documented on the basis of results of the serum trypsin-like immunoreactivity (TLI) assay 7. (dam 0.9 mg/L; sire 0.8 mg/L; control 5.2–35.0 mg/L). The dogs were fed regular commercial dog food twice daily, and 50 g of raw pig pancreas was added to every meal.

     At the time of mating, both dogs were clinically in good condition. The dam delivered 9 puppies, but 3 died immediately or a short time after birth. Necropsy was performed on these puppies, and histologic examination of the pancreas did not reveal abnormalities. 

     Of the 6 remaining puppies, 4 were females and 2 males. The puppies were weaned at 6 weeks of age and released to their owners. 

     The puppies were raised in private homes. The owners were informed orally about EPI and were also provided with a written information package. They were told that the dogs would likely be afflicted with EPI. The investigators and the dog owners maintained close ties throughout the study. All of the dogs lived in the Helsinki area.

     Two clinically healthy Beagles were included as control dogs. The dogs were sacrificed for an unrelated research project at the age of 3
years. The experimental protocol was approved by the Ethics Committee for Animal Experiments of the College of Veterinary Medicine, Helsinki, Finland.

Tests Performed on the Puppies
     Serum TLI was measured by radioimmunoassay.7. The tests were performed for the 1st time at 6 weeks of age.

     The biopsies from the pancreas were taken via laparotomy under general anesthesia. The gross appearance of pancreas was evaluated. One biopsy specimen was obtained from the right duodenal limb of the pancreas at each time point by ligation of a piece of pancreatic tissue (ca. 4.0mm in diameter) through a ventral midline abdominal incision. From all puppies the 1st biopsy was taken at 6 weeks of age and subsequently at approximately 0.5, 1.2, 2.0 years of age. Besides puppy no. 2 at 5.5 and 7.0 years of age. The biopsy specimens for histologic an electron microscopy (EM) examinations were processed in a routine manner.8. The EM findings of acinar cells were classified into 4 stages.8.

     Necropsy was performed on all dogs, and several samples of the pancreas were examined. The pancreas of 2 control dogs was also studied.

Results
    The dam developed a fatal mesenteric torsion 6 months after parturition. The sire was euthanized at the age of 12 years. Necropsy of both the dogs revealed a severely atrophic pancreas typical of an end-stage PAA.

    The results for puppy no. 1 have been published in detail elsewhere.8 Briefly, the female puppy was clinically healthy at birth and throughout adolescence, and grew normally without signs of maldigestion. The 1st biopsy from the pancreas at the age of 6 weeks was histological normal, but EM examination revealed mild stage 1 abnormalities. The dog was clinically normal at 22 months of age, but serum TLI was decreased to 0.3 mg/L (o2.5 mg/L indicating EPI; normal reference range 5.2–
35.0 mg/L). Examination of the pancreas indicated no gross or histologic abnormalities, but EM revealed widespread degenerative changes (stages 2–4). One month
later, the dog developed typical clinical signs of EPI, and at 25 months of age the gross and histologic examination of the pancreas revealed typical features of PAA.2 Treatment with powdered pancreatic extracta and antibiotics was introduced, with good treatment response.

     Puppy no. 2 (female) was clinically healthy during the 1st 5 years. Laparotomy was performed 4 times (at 1.5, 5,14, and 24 months of age). Gross and histologic examination was normal every time, and EM studies revealed stage 1 changes. Serum TLI was measured 12 times, and on 2 occasions the TLI value was subnormal (3.4 and 4.1 mg/L).

     At the age of 5.5 years, the dog was still clinically healthy and of normal weight, but serum TLI was abnormally low (2.1 mg/L) and at laparotomy, the gross
examination showed partial atrophy of the pancreas. There were scattered areas of pancreas that had lost their glandular appearance and changes typical for partial
PAA resulting from atrophic lymphocytic pancreatitis.1,2 Lymphocytic inflammation was most extensive in the border zone areas of normal and partially affected tissue.
EM showed evidence of atrophy, mainly type 3 and 4 degenerative changes. The islet cells were normal.

     The dog was treated with immunosuppressives (prednisolon  and azathioprined).9 Prednisolon treatment was discontinued after 1 year and azathioprine treatment
after 1.5 years.

     The dog lived another 6 years after diagnosis of partial AA. No signs of EPI were present. Serum TLI was measured 11 times; the values were always o5.2 mg/L, 5
times being abnormally low, o2.5 mg/L (range 0.2–2.4 mg/L).

     The dog died of internal hemorrhage at the age of 12 years. At necropsy the pancreas was severely diminished in size and histologic examination showed mild lymphocytic pancreatitis, especially in the border zone regions. In areas of more advanced tissue destruction, the findings were similar to those found in end-stage PAA.

     Puppy nos. 3 to 6 showed no clinical signs typical of EPI during their lifetime. A laparotomy was performed 4 times on each dog (between 6 weeks and 24 months of age), and the pancreas on every occasion was grossly normal, and a biopsy was taken. Histologic examinations revealed a normal pancreas. EM of the biopsies often
showed type 1 changes in acinar cells. After each laparotomy, recovery was uncomplicated and postoperative assays of serum amylase and lipase activities provided
no indication of pancreatitis or pancreatic tissue damage. Serum TLI was measured 7 to 15 times, and in each dog the value was at least once subnormal. The lowest values in dog nos. 3 to 6 were 2.7, 3.4, 3.4, and 4.9 mg/L, respectively. The dogs died due to different causes at ages 8 to 13 years. At necropsy, the pancreas was grossly and histologically normal in each dog.

     The TLI value of the 2 control dogs (7.5 and 8.4 mg/L) was within the normal range, and necropsy of the dogs revealed a normal pancreas both grossly and histologically. EM study of the control samples revealed evidence of type 1 changes.

Discussion
     Several previous studies have suggested that EPI is inherited in an autosomal recessive fashion. Here, when 2 affected EPI dogs were mated, only 2 of the 6 offspring
revealed atrophic changes in the exocrine part of the pancreas. This is much less than expected if a disease is inherited by Mendelian genetics. A polygenic mode of
inheritance is therefore the only explanation for this outcome. This is, however, a logical result as PAA in GSDs has been shown to be an autoimmune disease.2
     Performing test mating in dogs is laborious, particularly in late-onset diseases such as EPI. Test matings have been used more often in early-onset diseases, but also in these cases the keeping of affected animals purely for test purposes is ethically problematic. Fortunately, EPI is a treatable disease, and with medication an affected dog can live a more or less normal life. In our study, all dogs, including the two with degenerative changes in the pancreas, lived a normal life.

     Our previous report on puppy no. 1 described the rapid progression from EM findings to the gross appearance of a completely atrophied pancreas. We noted also
that mild stage 1 changes were found in acinar cells at the age of 6 weeks.8 To check whether the stage 1 changes were fixation artifacts instead of real degenerative changes, the pancreas of 2 healthy control dogs was examined. These dogs revealed similar changes. In conclusion, the changes earlier reported to be stage 1 changes are artifacts, thereby confirming that previous evidence indicating that PAA is a congenital disease in GSDs is not reliable.

     To halt the degenerative process on puppy no. 2, immunosuppressive medication was initiated. Whether the treatment was responsible for arresting the destruction process remains, however, unknown. Some dogs have been reported to stay in the subclinical phase of EPI for Exocrine Pancreatic Insufficiency 451
years, or sometimes for life, without treatment.9 Currently, no treatment is recommended when dogs with partial PAA have no clinical signs.9

    The other 4 siblings showed neither clinical signs typical of EPI nor degenerative or inflammatory changes in the pancreas. During their lifetime a pancreatic biopsy
was taken by laparotomy 4 times, and the pancreas was also examined at necropsy.

     To take serial biopsies from pancreas was the only reliable way to gain information about the pathological processes involved with the early stages of PAA before
the clinical signs of EPI appear. The 1st biopsies were taken after the weaning of the puppies to find out if EPI is a congenital disease. In an earlier study it was shown
that in about every 2nd EPI dog the clinical signs appear before 2 years of age.1 This is why we took almost all the biopsies during the 1st 2 years. During the study, the recovery from biopsy samplings was uneventful and no complications were detected.

      Measurement of serum TLI is the most commonly used test of pancreatic function, being both a sensitive and practical method for detecting severe EPI. We have reported that repeatedly low serum TLI values (o5.2 mg/L) in clinically healthy dogs can be a valuable marker of subclinical EPI and suggestive of partial PAA in GSDs.10 The results of puppy no. 2 are in agreement with this conclusion. During the last 6 years of its life the serum (TLI value was constantly low, fluctuating between subnormal (2.5–5.2 mg/L) and abnormally low (o2.5 mg/L). However, we have also concluded that diagnosing partial PAA may be problematic with an indirect pancreatic function test because of overlapping results in normal and partially affected dogs.10 This was also seen in these puppies, as each of the 4 healthy puppies had on at least some occasion subnormal serum TLI values.

     Our findings revealed that PAA is not a congenital disease in GSDs, and in this canine family PAA was not inherited by a simple autosomal recessive fashion of a
single gene. The study also showed that the atrophic process can destroy the entire exocrine part of the pancreas in a very short time, but the process can be halted, remaining in this position for the rest of the dog’s life. The function test helped to detect the stage of the exocrine pancreas, but it was not completely reliable.

From the Department of Equine and Small Animal Medicine (Westermarck, Wiberg) and the  Department of Basic Veterinary Sciences (Saari), Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland. Data for one of the dogs have previously been published in Am J Vet Res 1993;54:1088-1094. Corresponding author: Elias Westermarck, Department of Equine and Small Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, P.O. Box 57, 00014 Helsinki, Finland; e-mail: [email protected].
Submitted June 2, 2009; Revised September 3, 2009; Accepted
November 18, 2009.
Copyright r 2010 by the American College of Veterinary Internal
Medicine
10.1111/j.1939-1676.2009.0461.x
 

Footnotes
a Viokase V, Fort Dodge Laboratories, Fort Dodge, IA
b Tylan, Elanco, Geneva, Switzerland
c Prednisolon, Leiras, Tammisaari, Finland
d Azamun, Leiras

References
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in dogs. Vet Clin Small Anim 2003;33:1165–1179.
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atrophy in German Shepherd Dogs and rough-coated Collies: An
end result of lymphocytic pancreatitis. Vet Pathol 1999;36:530–541.
3. Weber W, Freudiger U. Erbanalytische Untersuchungen uber
die chronisce exocrine Pankreasinsuffizienz beim Deutshen Scha¨ ferhund.
Schweiz Arch Tierheilkd 1977;119:257–263.
4. Westermarck E. Hereditary nature of canine pancreatic degenerative
atrophy in the German Shepherd Dog. Acta Vet Scand
1980;21:389–394.
5. Moeller ME, Steiner JM, Clark LA, et al. Inheritance of pancreatic
acinar atrophy in German Shepherd Dogs. Am J Vet Res
2002;10:1429–1434.
6. Clark LA, Wahl JM, Steiner JM, et al. Linkage analysis and
gene expression profile of pancreatic acinar atrophy in the German
Shepherd Dog. Mammalian Genome 2005;16:955–962.
7. Williams DA, Batt RM. Sensitivity and specificity of radioimmunoassay
of serum trypsin-like immunoreactivity for the
diagnosis of canine exocrine pancreatic insufficiency. J Am Vet
Med Assoc 1988;192:195–200.
8. Westermarck E, Batt RM, Vaillant C, Wiberg M. Sequential
study of pancreatic structure and function during development of
panreatic acinar atrophy in German Shepherd Dog. Am J Vet Res
1993a;54:1088–1094.
9. Wiberg ME, Westermarck E. Subclinical exocrine pancreatic
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10. Wiberg ME, Nurmi AK, Westermarck E. Serum trypsin like
immunoreactivity measurement for the diagnosis of subclinical exocrine
pancreatic insufficiency. J Vet Intern Med 1999;13:426–432.
452 Westermarck et al