Which condition in males is characterized by low testosterone and small testes?

Klinefelter syndrome is characterized by the presence of an extra X chromosome in males, typically resulting in the chromosomal pattern 47,XXY. This condition leads to a variety of physical and developmental symptoms, including low testosterone levels and underdeveloped testes, known as hypogonadism. The low testosterone impacts a range of functions in the body, including the development of secondary sexual characteristics, muscle mass, and reproductive capabilities. Additionally, individuals with Klinefelter syndrome may have taller stature and less body hair than average.

In contrast, Turner syndrome primarily affects females and is associated with a complete or partial absence of one X chromosome, presenting with entirely different symptoms. Down syndrome is characterized by an extra copy of chromosome 21 and has its own distinct features and health concerns. Marfan syndrome affects connective tissue and has features such as tall stature and long limbs but is unrelated to testosterone levels or testicular size. Thus, Klinefelter syndrome is the only condition in this list that aligns with low testosterone and small testes in males.