A nurse comments that the only aneuploid conditions he has seen in his practice are Patau syndrome, Edwards syndrome, and Down syndrome. What rationale would the genetics specialist suggest?

Question

1. The diagnosis of aneuploidy is made early in the pregnancy, so women whose fetuses demonstrate other conditions are referred to high-risk providers.
2. These are all monosomic conditions, which have a higher survival rate to delivery.
3. The chromosomes affected are small.
4. Spontaneous abortions are rare among fetuses with these conditions.

Answer 1

3
Rationale 1: Often aneuploidy is not diagnosed until the infant is born. There is no indication that this nurse does not work in a high-risk unit.
Rationale 2: These are trisomic conditions.
Rationale 3: Chromosomes 13, 18, and 21 are the smallest of all chromosomes with respect to the numbers of genes they encode for. Thus a deficit of these particular chromosomes may enhance survivability.
Rationale 4: Spontaneous abortions do occur in fetuses with these conditions, but many affected fetuses survive to delivery.