Which disorder is caused by a presence of an extra X chromosome in males?

The presence of an extra X chromosome in males leads to Klinefelter syndrome. Normally, males have one X and one Y chromosome (46, XY), but individuals with Klinefelter syndrome typically have one or more additional X chromosomes, resulting in a karyotype of 47, XXY in the most common form.

This chromosomal variation affects physical and cognitive development, often leading to features such as reduced testosterone levels, infertility, and in some cases, breast tissue development and increased height. The syndrome can also be associated with learning difficulties or developmental delays, although many individuals may have mild symptoms or be undiagnosed.

It is important to differentiate Klinefelter syndrome from the other disorders listed. Turner syndrome, for instance, results from the absence of one of the X chromosomes in females (45, X). Down syndrome is caused by an extra copy of chromosome 21 (trisomy 21), and Edwards syndrome involves an extra copy of chromosome 18 (trisomy 18). Each of these conditions has distinct chromosomal abnormalities and phenotypes, highlighting the unique nature of Klinefelter syndrome in the context of an additional X chromosome in a male's genetic makeup.