Biliverdinuria Caused by ExonicDeletions in Two Dogs with Green Urine.

Abstract

In heme degradation, biliverdin reductase catalyzes the conversion of biliverdin to bilirubin. Defects in the biliverdin reductase A gene () causing biliverdinuria are extraordinarily rare in humans, and this inborn error of metabolism has not been reported in other mammals. The objective of this study was to diagnose biliverdinuria and identify the causalvariants in two adult mixed-breed dogs with life-long green urine. One of the dogs also had an unexplained regenerative anemia and mild hepatopathy.Clinicopathological evaluations, urinary mass spectroscopy, and molecular genetic studies were performed. Urine metabolic screening identified increased biliverdin concentrations in both cases relative to control dogs.Whole genome and Sanger sequencing revealed that each case was homozygous for large deletions in: UU_Cfam_GSD_1.0/canFam4 chr18:6,532,022-6,551,313 (19,292 bp) in Case 1 and chr18:6,543,863-6,545,908 (2046 bp) in Case 2. These variants were predicted to result in majortruncations (ENSCAFT00805017018.1 p.[Lys117-Lys296del] and p.[Ala154fs], respectively) and loss of enzyme function. In a genomic variant database, 671 dogs from 63 breeds had coverage over these regions, ruling out homozygosity for thedeletions. A gene defect for the regenerative anemia in Case 1 was not discovered.While expected to be rare, genotyping for thedeletions can be used to identify other affected and carrier dogs. This study illustrates the use of targeted metabolic and genomic screening as key diagnostic tools to diagnose a rare metabolic disorder. These are the first confirmed cases of biliverdinuria caused bydefects in non-human mammals.