Jacobs Syndrome (XYY Syndrome or 47XYY)
People with Jacobs Syndrome develop with an extra Y chromosome. They may not have any obvious physical variations as a result, but might be taller than usual or have other identifiable differences unrelated to sex characteristics. Some individuals with Jacobs Syndrome may also have a smaller-than-typical penis or scrotum, hypospadias, and/or undescended testicles. Source