The objective of this study is to A) clinicopathologically and molecularly characterize microphthalmia with delayed growth in the Portuguese Water Dog (POWD) and B) develop a DNA-based test to assist breeders with their breeding programs and avoid producing affected dogs.
Objective A is not complete due to the illness of one of the collaborators. However, we are finalizing a draft of the paper describing the clinical findings and the molecular defect. A paper was published about microphthalmia in POWDs 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) at 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-like 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 POWD. This allowed us to find a variant in a gene that is important for the development of the eye, and this variant is not present in any of the normal dogs including dogs of other breeds.
We have made the test available to the breeders early in 2020 and have already tested 1,112 POWDs from at least 10 different countries to date. Of the dogs tested, 926 were tested as clear, 184 carriers, and 2 affected.