Current Knowledge and Pathophysiology

Introduction
Portosystemic shunts (PSS) are naturally occurring abnormalities that allow portal blood to bypass the liver and to enter the systemic circulation directly. One of the first descriptions of a congenital PSS was given in 1793 by the London surgeon John Abernethy. He described the postmortem findings in a 10-months-old girl with multiple congenital abnormalities, including a portocaval shunt. The first case in a dog was reported by Hickman in 1949 and in a cat by Vulgamott in 1980 . Other species in which PSS have been described are the horse, the cow and the pig.

PSS may be congenital or acquired. This abstract focuses on congenital PSS in the dog and cat. Congenital PSS (CPSS) are relatively rare with a reported prevalence in dogs of 0,18%. The proportion of CPSS diagnosis has increased ten-fold from 5 per 10.000 dogs in 1980 to 5 in 1000 dogs in 2001.

Inheritability
The congenital nature and the occurrence in specific breeds suggest a hereditary condition, but this was only demonstrated in a few breeds. Van Steenbeek et al. showed that intrahepatic portosystemic shunts in the Irish Wolfhound are a familial disorder that is likely genetic. It was not considered likely that the mode of inheritance was monogenetic. A digenic, triallelic trait could explain the observed occurrence of shunts in two litters but other modes of inheritance could not be excluded. A striking detail was that both left- and right-sided shunts occurred in the same litter. In a group of 6,367 Cairn terriers, a significantly higher prevalence of CPSS was found in three large family groups compared with the general population. It was concluded that CPSS is a genetic disease in Cairn terriers and that the mode of inheritance is autosomal and most likely polygenetic or monogenetic with variable expression.  [...]