What is the most common sex aneuploidy observed in both conception and live births?

Klinefelter syndrome is recognized as the most common sex aneuploidy seen in both conceptions and live births. This condition arises from the presence of an extra X chromosome in males, typically resulting in a karyotype of 47,XXY. The prevalence of Klinefelter syndrome at conception is estimated to be significantly higher than the numbers of affected births, as many conceptions with this aneuploidy do not lead to live births due to various complications.

In contrast, while Turner syndrome, which is characterized by a missing X chromosome in females (45,X), is also common, it tends to result in a higher rate of miscarriage compared to Klinefelter syndrome, leading to fewer live births. Down syndrome, which is a trisomy of chromosome 21, is related to a different mechanism and is not classified as a sex aneuploidy; it is more prevalent in conceptions than in live births as well, but does not specifically pertain to sex chromosomes. Triple X syndrome (47,XXX), though a sex aneuploidy, has a lower incidence in live births compared to Klinefelter syndrome.

Therefore, Klinefelter syndrome stands out as the most commonly observed