Trisomy 21 is also known as: September 2011
**Core Concept**
Down syndrome, also known as Trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. This extra genetic material disrupts normal development and function of various organs and tissues, leading to characteristic physical and intellectual disabilities.
**Why the Correct Answer is Right**
The extra copy of chromosome 21 results in an overexpression of genes that regulate cell growth, differentiation, and survival. This leads to an increased risk of various medical complications, including heart defects, vision and hearing problems, and an increased risk of leukemia. The overexpression of these genes also contributes to the characteristic intellectual disability and developmental delays seen in individuals with Down syndrome.
**Why Each Wrong Option is Incorrect**
**Option A:** There is no other widely recognized name for Trisomy 21 besides Down syndrome.
**Option B:** Edwards syndrome, also known as Trisomy 18, is a different genetic disorder caused by an extra copy of chromosome 18.
**Option C:** Patau syndrome, also known as Trisomy 13, is another genetic disorder caused by an extra copy of chromosome 13.
**Option D:** Turner syndrome, also known as 45,X, is a genetic disorder caused by the absence of one X chromosome in females.
**Clinical Pearl / High-Yield Fact**
The risk of Down syndrome increases with maternal age, especially after the age of 35. This is because the risk of nondisjunction, which leads to Trisomy 21, increases with age.
**Correct Answer: D. Turner syndrome, also known as 45,X, is a genetic disorder caused by the absence of one X chromosome in females.**