The pathogenesis of congenital portosystemic shunt (CPSS) is not completely understood but is believed to be hereditary because it is more commonly diagnosed in specific breeds. Furthermore, there is a clear distribution of extra- and intrahepatic shunts within the various breed populations, with extrahepatic shunts found more commonly in small breeds and intrahepatic shunts in large breeds. Studies of Irish wolfhounds and Yorkshire terriers have concluded that the anomaly is hereditary in these 2 breeds. Cairn terriers also have a higher incidence of extrahepatic CPSS, but a hereditary basis and the mode of inheritance have not been identified.

Between July 1990 and July 2001, 6367 6-week-old Dutch cairn terrier puppies (representing more than 80% of the Dutch cairn terrier population in those years) were screened for CPSS. In the presence of hyperammonemia, venous ammonia concentrations and ammonia tolerance tests were followed with definitive diagnosis using ultrasonography, exploratory celiotomy, portal vein angiography, or postmortem examination. Of this population, 58 dogs were diagnosed with CPSS (32 males, 26 females). From these, 6 family groups were chosen to investigate family-related differences in the frequency of shunts as compared with the general population. In addition, 3 test matings were done with a female with CPSS with an unrelated affected male, her unaffected sire, and an affected offspring. From the statistical analysis of their study, the authors found a significantly higher prevalence of CPSS in 3 of the family groups (5.9%, 5.5%, and 1.9%) than in the general population (0.58%). They also found a significantly higher prevalence of CPSS in the offspring of the test matings (21.1%) than in the general population. There was no sex predilection among affected dogs. On the basis of their data, the authors concluded that CPSS in cairn terriers is a genetic disease with an autosomal mode of inheritance and most likely polygenic or monogenic with variable expression.

COMMENTARY: Prevalence of single congenital portosystemic shunts (CPSS) in cairn terriers is significantly greater than in mixed breed dogs, indicating that a hereditary basis for the disease is likely in this breed. This study confirms that heredity of CPSS in cairn terriers, as in Yorkshire terriers, is not simple dominant, simple recessive, or X-linked. Also, as in Irish wolfhounds, some family lines are at increased risk for development of the disease. Although the exact mode of inheritance of CPSS has yet to be determined, this study brings us another step closer to understanding its genetic underpinnings.

Inherited congenital extrahepatic portosystemic shunts in cairn terriers. van Straten G, Leegwater PAJ, de Vries M, et al. J VET INTERN MED 19:321-324, 2005.