Gregory and his Extra X is a children's book for kids with XXY (Klinefelter syndrome). This book helps children and adolescents with XXY understand their condition. The story follows Gregory, a young boy with XXY, through his busy day as he attends school, goes to golf practice and has a doctor's appointment. The story explores the genetics of XXY and addresses social, academic and medical aspects of this condition in an age-appropriate, fun way. Though Gregory's condition presents him with many challenges throughout the story, he is able to work through each challenge in his own way. Boys with XXY will identify with and learn from Gregory as they read this book.