What characteristic of Klinefelter's syndrome affects males?

Klinefelter's syndrome is a condition that arises from the presence of an extra X chromosome in males, typically resulting in a genotype of 47,XXY. One of the primary characteristics of this syndrome is reduced fertility, which is attributed to testicular dysgenesis. Males with Klinefelter's syndrome may have smaller testes and lower levels of testosterone compared to typical males, leading to diminished sperm production and subsequently, reduced fertility.

Additionally, many individuals with Klinefelter's syndrome often experience learning difficulties, particularly in language and reading skills. This can stem from developmental delays and may be associated with an increased risk of various learning disabilities. These combined factors of reduced fertility and potential learning difficulties characterize the impact of Klinefelter's syndrome on males, making this the correct answer.