Klinefelter syndrome is a genetic disorder caused by an additional X chromosome on an XY background (44 + XXY).
Therefore, this condition affects only males.
Males suffering from this syndrome have characteristics of females such as breast development, wide hips, thinly dispersed hairs and reduced muscle mass.
They have low testosterone, producing no sperms and thus, are sterile males.
It occurs due to some error during cell division at the time of gamete formation.