## **Core Concept**
Patau syndrome, also known as trisomy 13, is a genetic disorder caused by an extra copy of chromosome 13. This condition leads to severe intellectual disability and physical abnormalities. The chromosomal karyotype is crucial for diagnosing genetic disorders.

## **Why the Correct Answer is Right**
The correct answer is **47,XX,13+** or simply represented as **47,XX,+13** (or **47,XY,+13** for males), indicating an extra copy of chromosome 13. This karyotype signifies trisomy 13, which is the genetic basis of Patau syndrome. The presence of an extra chromosome 13 disrupts the normal development of the fetus, leading to the characteristic features of the syndrome.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option does not specify the correct chromosomal abnormality associated with Patau syndrome. Without the specific details, it's incorrect.
- **Option B:** This option likely refers to a different chromosomal abnormality. Trisomy 18, or Edwards syndrome, is associated with a different set of physical and developmental problems.
- **Option D:** Similarly, this option does not correspond to the chromosomal karyotype for Patau syndrome.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Patau syndrome is one of the three main trisomies (along with trisomy 21/Down syndrome and trisomy 18/Edwards syndrome) that are commonly tested for in prenatal screening. The presence of severe congenital anomalies and poor prognosis makes early diagnosis crucial.

## **Correct Answer:** . **47,XX,+13**