What is the most common aneuploidy observed overall?

Down Syndrome, caused by the presence of an extra copy of chromosome 21 (trisomy 21), is the most common aneuploidy observed overall. The condition is characterized by various developmental and physical features, including distinct facial traits, intellectual disability, and a higher prevalence of certain health issues, such as heart defects and gastrointestinal problems.

In terms of prevalence, Down Syndrome occurs in approximately 1 in 700 live births, making it the most frequently occurring chromosome disorder. This is significantly higher than the other disorders listed. Turner Syndrome, which involves the absence of one X chromosome in females (typically resulting in a 45,X karyotype), is another chromosomal condition, but it is less common, affecting about 1 in 2,500 live female births. Patau Syndrome, associated with trisomy 13, and Edward's Syndrome, linked to trisomy 18, are much rarer, with occurrences around 1 in 5,000 and 1 in 6,000 live births, respectively.

Thus, understanding the prevalence and characteristics of these conditions is critical in genetic counseling, particularly when discussing risks with prospective parents and informing them about the implications of chromosomal abnormalities.