Mandy Moore revealed that her two-year-old son Gus has Gianotti-Crosti Syndrome, a rare skin condition that causes a blistering and itchy rash in children according to WebMD. In posts on her Instagram Story, the 39-year-old actress detailed how Gus, whom she shares with her husband Taylor Goldsmith, woke up with a mysterious rash on Saturday, which was initially difficult to diagnose despite visits to several doctors. "This sweet boy woke up with a crazy rash on Saturday am," the "This Is Us" star wrote on a photo of Gus licking a lollipop in what appeared to be a doctor's office.