XYY syndrome, also known as Jacobs syndrome and Superman syndrome, is an aneuploid genetic condition in which a male has an extra Y chromosome. There are usually few symptoms. These may include being taller than average and an increased risk of learning disabilities. Most individuals with this condition have normal fertility.
Treatment may include speech therapy or extra help with schoolwork, and outcomes are generally positive. The condition occurs in about 1 in 1,000 male births. Many people with the condition are unaware that they have it. The condition was first described in 1961.
Some medical geneticists question whether the term "syndrome" is appropriate for this condition, because many people with this karyotype appear normal.
The false stereotype of XYY boys and men as violent criminals has also been used as a plot device in the horror films Il gatto a nove code in February 1971 (dubbed into English as The Cat o' Nine Tails in May 1971) and Alien 3 in May 1992. The main character of the 2005 film Neo Ned is a neo-nazi who has an extra Y chromosome.
















