XXXY syndrome is a genetic condition characterized by a sex chromosome aneuploidy, where males have two extra X chromosomes. Males typically have only two sex chromosomes, an X and a Y. The presence of one Y chromosome with a functioning SRY gene causes the expression of genes that determine maleness. Because of this, XXXY syndrome only affects males. The additional two X chromosomes in males with XXXY syndrome causes them to have 48 chromosomes, instead of the typical 46. XXXY syndrome is therefore often referred to as 48,XXXY. There is a wide variety of symptoms associated with this syndrome, including cognitive and behavioral problems, taurodontism, and infertility. This syndrome is usually inherited via a new mutation in one of the parents’ gametes, as those affected by it are usually infertile. It is estimated that XXXY affects one in every 50,000 male births.