Like humans, dogs are occasionally born with birth defects, and they occur more frequently in some breeds. In the case of XX DSD, a disorder of sexual development, affected puppies that have normal female sex chromosomes (XX) are born with masculinized genitals and are often infertile or sterile. XX DSD is a documented problem for 28 breeds of purebred dogs, including in particular American cocker spaniels and German shorthaired pointers. Dr. Vicki Meyers- Wallen’s work focuses on tracking down the genetic reasons for XX DSD so that the disorder can be avoided or eventually eliminated from purebred dogs.
- Locating the genetic “marker” for a genetic disorder. Meyers- Wallen identified four dogs, some affected with XX DSD and some not, and sequenced their genomes – the entire DNA sequences in their cells. By comparing those sequences, Meyers-Wallen identified those that affected dogs have in common but which were not present in normal dogs and she then pinpointed the region and a specific sequence difference (marker) that could be responsible for XX DSD. She then found that same marker in affected dogs of several breeds, confirming the marker’s role in canine XX DSD.
- XX DSD changes how cells express their DNA information. Meyers- Wallen studied reproductive organ development in dog embryos and found that cells that carry the XX DSD marker express genes differently than normal cells, explaining the abnormal development of the reproductive organs in the dogs with those mutations. This discovery will allow a genetic test to be developed to identify carrier animals, allowing for breeding of unaffected animals to avoiding this disease in the future.