Mr. and Mrs. Annadurai have a 2 month old baby suffering from Down’s syndrome. Karyotype of Mrs. Annadurai shows translocation variety of Down syndrome. Which of the following investigations will you advise to the parents before the next pregnancy?
**Core Concept**
Down syndrome, also known as trisomy 21, is a genetic disorder caused by an extra copy of chromosome 21. There are three main types: trisomy 21 (95%), mosaicism (3%), and translocation (2%). Translocation occurs when a part of chromosome 21 breaks off and attaches to another chromosome, usually chromosome 14, 21, or 22.
**Why the Correct Answer is Right**
In the case of translocation Down syndrome, the risk of recurrence is higher if the translocation is balanced (no extra genetic material) or if there is a carrier of a Robertsonian translocation. To assess this risk, a genetic study called a **chromosomal analysis** or **karyotyping** is essential. This test will reveal if the parents have a balanced translocation or are carriers, which can guide counseling and planning for future pregnancies.
**Why Each Wrong Option is Incorrect**
**Option A:** **Prenatal ultrasound** is crucial for identifying fetal anomalies but does not assess genetic risks or provide information about parental carrier status.
**Option B:** **Genetic counseling** is essential, but this option does not specify the investigation to be performed.
**Option C:** **Fetal blood sampling** is a diagnostic test for fetal infections and anemia but is not relevant for assessing genetic risks in translocation Down syndrome.
**Clinical Pearl / High-Yield Fact**
In cases of translocation Down syndrome, it's essential to remember that the risk of recurrence is higher if the parents have a balanced translocation or are carriers. This information can be obtained through chromosomal analysis or karyotyping.
**Correct Answer:** C. Chromosomal analysis or karyotyping.