One of the parents who have a child with Down syndrome, has a balanced translocation between chromosome 15 and 21. What advice will you provide to the couple to prevent a child being born with Down syndrome?
**Core Concept**
Down syndrome is a genetic disorder caused by an extra copy of chromosome 21, known as trisomy 21. Balanced translocations involving chromosome 21 can lead to an increased risk of passing on an abnormal number of chromosome 21 to offspring, resulting in Down syndrome.
**Why the Correct Answer is Right**
A balanced translocation between chromosome 15 and 21 is a type of chromosomal rearrangement where a segment of chromosome 15 is exchanged with a segment of chromosome 21. This can lead to an increased risk of producing gametes (sperm or eggs) that are unbalanced, meaning they have an abnormal number of chromosome 21. If such a gamete is fertilized, it can result in a child with Down syndrome. Therefore, genetic counseling and testing are essential for this couple to understand their risk and consider prenatal testing.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a balanced translocation between chromosome 15 and 21 does not directly affect the risk of Down syndrome. While a balanced translocation can increase the risk, it is not a guarantee.
**Option B:** This option is incorrect because there is no established evidence that suggests a specific diet or lifestyle change can prevent Down syndrome. While a healthy lifestyle is essential for overall well-being, it does not directly impact the risk of Down syndrome.
**Option C:** This option is incorrect because prenatal testing can only detect Down syndrome in the fetus, but it cannot prevent it. Couples with a history of balanced translocations should consider genetic counseling and family planning options.
**Clinical Pearl / High-Yield Fact**
Couples with a history of balanced translocations should undergo genetic counseling and consider prenatal testing, such as amniocentesis or chorionic villus sampling, to assess the risk of passing on an abnormal number of chromosome 21 to their offspring.
**Correct Answer: D.** Genetic counseling and testing are essential for this couple to understand their risk and consider prenatal testing.