USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What karyotype is typically found in individuals with Klinefelter syndrome?

1. 46,XX

2. 47,XXY

3. 45,XO

4. 46,XY

The correct answer is: 47,XXY

Individuals with Klinefelter syndrome typically have a karyotype of 47,XXY. This condition arises from an extra X chromosome in males, leading to the presence of two X chromosomes alongside the usual male XY chromosome pair. The additional X chromosome results in various physiological and developmental features associated with Klinefelter syndrome, such as hypogonadism, reduced testosterone levels, and potentially some cognitive challenges. The presence of additional sex chromosomes can disrupt normal male development, resulting in a range of symptoms including gynecomastia, infertility, and taller-than-average stature. This karyotype is distinct and diagnostic for Klinefelter syndrome, helping healthcare providers recognize and manage the condition appropriately. Other karyotypes mentioned do not represent this syndrome; for example, 46,XX would indicate a typical female karyotype, 45,XO (Turner syndrome) represents a missing X chromosome in females, and 46,XY is a typical male karyotype without the genetic anomaly seen in Klinefelter syndrome.