Health Ongoing Studies

Genetics of Portosystemic Vascular Anomalies and Microvascular Dysplasia in Small Breed Dogs

Portosystemic vascular anomalies (PSVAs) and microvascular dysplasia (MVD) are related genetic disorders that cause abnormal liver circulation in small terrier breeds of dogs. The prevalence ranges from 30 to 80 percent. Many dogs with PSVA are overtly ill because the liver cannot remove toxins from food. Dogs with MVD, on the other hand, may only demonstrate intolerance to standard drug dosages. In the first phase of the study, researchers from Cornell University prepared DNA from 44 Cairn terriers (22 dogs affected with PSVA and 22 matched unaffected sibling controls) and 22 dogs (11 affected and 11 unaffected sibling controls) from four additional breeds—Yorkshire terriers, Tibetan spaniels, Maltese and Norfolk terriers—for genotyping analysis. There have been some delays due to a robotic malfunction in the genomic analysis instrumentation, which required some DNA samples to be resubmitted for analysis. Using the incomplete data set, the researchers were able to identify four regions of interest on three different chromosomes. Once the full data set becomes available later this summer, the researchers will begin fine-mapping these chromosomal regions in hopes of further narrowing the regions of interest. The investigators are also continuing their overlap analysis, comparing results of two different genomic analysis techniques on samples from affected and unaffected Cairn terriers and Tibetan spaniels. Candidate genes identified by overlap analysis will be sequenced to identify potential genetic mutations. To date, the investigators have completed the sequencing of three candidate genes; however, none of these genes was found to be responsible for PSVA or MVD. Once genetic mutations responsible for these abnormalities are identified, the investigators plan to develop affordable genetic tests that can identify carrier animals. These tests would be used to make breeding decisions that would reduce and eventually eliminate the occurrence of these liver disorders in these breeds. The study is also providing a research associate and an assistant professor, both of whom are in the early stages of their scientific careers, with valuable training in veterinary molecular genetics and in the mapping of complex traits.

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