Klinefelters Syndrome (Gonadal Dysgenesis) - Klinefelter syndrome, also known as the XXY condition, is a term used to describe males who have an extra x-chromosomes in most of their cells. Instead of having the usual XY chromosome pattern that most males have, these men have an XXY pattern. Klinefelter syndrome is named after Dr. Henry Klinefelter, who first described a group of symptoms found in some men with the extra X chromosome. Even though all men with Klinefelter syndrome have the extra X chromosome, not every XXY male has all of those symptoms. .