Mr. and Mrs. Mehtha have a 2 month old child with Down’s syndrome. Karyotype of Mrs Mehtha 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 is a genetic disorder caused by an extra copy of chromosome 21, resulting from a nondisjunction event during meiosis. However, in some cases, the condition is caused by a translocation, where part of chromosome 21 breaks off and attaches to another chromosome, usually chromosome 14.
**Why the Correct Answer is Right**
In the translocation variety of Down syndrome, the risk of recurrence is higher, especially if one of the parents is a carrier of the balanced translocation. To assess the risk, a karyotype analysis of the parents is essential. The parents should undergo a chromosomal analysis to determine if they are carriers of the balanced translocation. If the father is a carrier, the risk of recurrence is significantly higher, and the mother may be at risk of having a child with unbalanced translocation.
**Why Each Wrong Option is Incorrect**
**Option A:** Amniocentesis is a prenatal test that can diagnose chromosomal abnormalities, but it is not the first-line investigation for assessing the risk of recurrence in parents with a history of Down syndrome due to translocation.
**Option B:** Serum screening tests, such as maternal serum alpha-fetoprotein (MSAFP) and human chorionic gonadotropin (hCG), can identify pregnancies at higher risk for Down syndrome, but they do not provide information on the genetic cause of the condition.
**Option C:** Ultrasound evaluation can identify some physical characteristics associated with Down syndrome, but it does not provide information on the genetic cause of the condition or assess the risk of recurrence.
**Option D:** Molecular genetic testing can detect the presence of specific genetic mutations, but it is not the first-line investigation for assessing the risk of recurrence in parents with a history of Down syndrome due to translocation.
**Clinical Pearl / High-Yield Fact**
Parents with a history of Down syndrome due to translocation should be advised to undergo chromosomal analysis before the next pregnancy to assess the risk of recurrence.
**Correct Answer: C. Ultrasound evaluation can identify some physical characteristics associated with Down syndrome, but it does not provide information on the genetic cause of the condition or assess the risk of recurrence.**