Which trisomy disorder is commonly known as Down syndrome?

Down syndrome, also known as trisomy 21, results from the presence of an extra chromosome 21 in an individual’s genetic makeup. Typically, humans have 46 chromosomes, arranged in 23 pairs. In Down syndrome, instead of the typical two copies of chromosome 21, there are three copies. This additional genetic material alters the course of development and has various effects on a person's physical characteristics and cognitive abilities.

Individuals with Down syndrome often exhibit distinctive physical features such as a flattened face, slanted eyes, and a shorter stature. There may also be developmental delays and increased risk of certain medical conditions, like heart defects. The diagnosis is usually confirmed through genetic testing, which can identify the extra chromosome.

Trisomy disorders, such as Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome), are caused by additional chromosomes but are associated with more severe developmental issues and generally have a much lower survival rate; thus, they are distinct from Down syndrome. Monosomy X, also known as Turner syndrome, involves the absence of one of the two sex chromosomes and is also a different genetic condition altogether.