is a chromosomal condition, characterized by the presence of an extra X and Y chromosome in males, that causes medical and behavioral problems. 48,XXYY can be considered a variant of Klinefelter syndrome. Individuals with 48,XXYY are usually considerably tall with small testes that do not function normally leading to infertility. In addition, affected individuals have behavioral problems such as anxiety, aggressiveness, problems communicating, hyperactivity, depression, as well as general learning disabilities and intellectual impairment. Other medical probelms can include congenital heart defects, bone abnormalities, tremor, obesity, type 2 diabetes and/or respiratory problems. Patients have an essentially normal life expectancy but require regular medical follow-up. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.