Klinefelter syndrome, also known as XXY syndrome, is a condition in boys and men that’s caused by an extra X chromosome. It can affect physical and mental development.

Klinefelter syndrome is the most commonly occurring sex-chromosome disorder, and it often goes undiagnosed. In this article the authors discuss the diagnosis and the clinical features and ...

Klinefelter syndrome is the most common sex chromosome disorder in men, affecting approximately one in 600 male births. The condition results from being born with an extra X chromosome, leading to ...

Klinefelter's syndrome, named after Harry F. Klinefelter, who first described the syndrome in 1942, [1,2] is the most frequent major abnormality of sexual differentiation in men with two or more ...

Klinefelter syndrome is a genetic condition that occurs when a male is born with an extra copy of the X chromosome, affecting an estimated 1 in 1,000 individuals. Symptoms of Klinefelter syndrome may ...

However, the authors cited a 2022 study regarding a skeleton from early medieval Finland with possible Klinefelter syndrome who was buried with both masculine and feminine grave goods.

Klinefelter Syndrome. The symptoms and characteristics of Klinefelter syndrome vary widely among males with the disorder. Many boys with the syndrome show few or only mild signs.