What is the typical phenotype of Klinefelter syndrome?

The typical phenotype of Klinefelter syndrome is best represented by a male with some female characteristics. This condition typically arises from the presence of one or more extra X chromosomes in males, resulting in a 47,XXY karyotype or variants like 48,XXXY.

Individuals with Klinefelter syndrome generally present as males but may exhibit features that are more commonly associated with females. These features can include breast tissue development (gynecomastia), reduced testosterone levels, wider hips, and decreased muscle mass. Additionally, there may be some impact on fertility, with many affected individuals experiencing reduced sperm production or infertility.

The diagnosis is often confirmed through karyotyping, which reveals the chromosomal makeup, reflecting the presence of an additional X chromosome. While the syndrome can result in a range of symptoms and severity, the presence of some female characteristics is a defining aspect of the phenotype associated with Klinefelter syndrome.