The inheritance of extra‐hepatic portosystemic shunts and elevated bile acid concentrations in Maltese dogs

OBJECTIVES: To determine the heritability of extra‐hepatic portosystemic shunts and elevated post‐prandial serum bile acid concentrations in Maltese dogs. MATERIALS AND METHODS: Maltese dogs were recruited and investigated by a variable combination of procedures including dynamic bile acid testing, rectal ammonia tolerance testing, ultrasonography, portal venography, surgical inspection or necropsy. In addition, nine test matings were carried out between affected and affected dogs, and affected and unaffected dogs. RESULTS: In 135 variably related Maltese, shunt status could be confirmed in 113, including 19 with an extra‐hepatic portosystemic shunt (17 confirmed at surgery, 2 at necropsy). Rectal ammonia tolerance testing results and post‐prandial serum bile acid concentrations were retrievable for 50 and 88 dogs, respectively. Pedigree information was available for these 135 and an additional 164 related dogs. Two consecutive test matings were carried out between two affected animals (whose shunts had been attenuated), with 2 of 8 (25%) of offspring having an extra‐hepatic portosystemic shunt. Six test matings were carried out between an affected and an unaffected animal, with 2 of 22 (9%) offspring affected. Heritability of extra‐hepatic portosystemic shunt was 0·61 calculated using variance components analysis [95% confidence interval (CI) 0·14 to 1·0, P=0·001]. The best fitting model from segregation analysis was a common, partially penetrant, recessive model (allele frequency 0·34, penetrance 0·99, CI 0·09 to 1·0). The heritability of elevated post‐prandial serum bile acid (and thus likely portal vein hypoplasia) was 0·81 (CI 0·43 to 1·0, P=0·2) after logarithmic transformation of post‐prandial serum bile acid concentrations. CLINICAL SIGNIFICANCE: There is strong support for extra‐hepatic portosystemic shunts and elevated post‐prandial serum bile acid concentrations both being inherited conditions in Maltese.