Research Update August 2019 CHF-02403-MOU: Microphthalmia and Delayed Growth Syndrome in the Portuguese Water Dog (Puppy Eye Syndrome)

The objective of this study is to A) clinicopathologically and molecularly characterize microphthalmia with delayed growth in the Portuguese Water Dog (PWD) and B) develop a DNA-based test to assist breeders with their breeding programs and avoid producing affected dogs.

Objective A is over 100% complete. A draft of the paper describing the clinicopathological findings had been written but we found more data on affected puppies, which were added to the paper. A paper was published about microphthalmia in PWDs recently by a group out of Cornell. However, this paper described only the ocular changes in affected dogs. With our publication, we will show that there can be other abnormalities such as low platelet counts and stunted growth, which makes this a truly syndromic disorder. We have also included pedigree analyses showing the autosomal recessive mode of inheritance. In the meantime, we have decided to put all of the clinical data into the final paper describing the disease-causing variant, making this a large landmark paper.

For Objective B, we received enough DNA samples from affected dogs and their relatives to perform an initial genome wide association study (GWAS). The DNA was sent to Illumina (Neogen) the end of November 2018, and we received the results as expected in January 2019. We are absolutely thrilled with the results: A single, very significant peak was seen on the “Manhattan plot”, which allows us to locate not only the chromosome but the general area of that chromosome in which the gene must be located. Indeed, there is a gene in this area that, when mutated in mice and humans, causes a microphthalmia syndrome. We sequenced this gene and did not find a clear disease-causing variant. Thus, we submitted and sequenced the entire genome of one affected dog and one normal PWD. We have received the data and are analyzing it. To put it in perspective, these are about 3 billion base pairs that need to be analyzed – this requires a substantial computing- and manpower. However, we are confident that we will find the disease-causing gene.