Kleinfelter's Syndrome is a genetic disorder in males, where there are three sex chromosomes XXY, instead of the normal XY in males, or XX in females. Having an extra X chromosome affects physical and cognitive development.
Individuals affected with Kleinfelter's Syndrome usually have smaller testes that produce less of the male hormone testosterone, which leads to symptoms like breast enlargement, reduced facial and body hair, and infertility. Boys with the syndrome may have weaker muscles and as they age, tend to grow taller than their peers. They may also have problems with learning and language.