An excess of which of the following causes so many wrinkles in the shar-pei breed?

The traditional shar-pei that is most popular in China is more faithful to the history of the breed (taller, less wrinkly, flatter mouth and nose, horse-coated). As puppies, they have lots of wrinkles and as they get older, they have fewer wrinkles.

Scientists from the Department of Genome Sciences at the University of Washington, Seattle, announced in January 2010 that they had analysed the genetic code of 10 different pedigree dog breeds. In the shar-pei, they discovered four small differences located in the gene HAS2, which is responsible for making hyaluronic acid synthase 2. That enzyme makes hyaluronic acid, which is one of the key components of the skin. There have been rare cases in which a mutation of the same gene has caused severe wrinkling in humans as well.