American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

Which nomenclature is correct for a patient with Down syndrome with only trisomy 21 found?

1. 46,XY,+21

2. 47,XX,+21

3. 47,XY,+21c[20]

4. 48,XY,+21

The correct answer is: 47,XY,+21c[20]

The correct nomenclature for a patient with Down syndrome resulting from the presence of an extra chromosome 21 is "47,XY,+21." This is because Down syndrome is typically characterized by trisomy 21, which means there are three copies of chromosome 21 instead of the normal two. In this case, the initial number indicates the total number of chromosomes, which is 47 due to the extra chromosome. The "XY" signifies the sex chromosomes, indicating a male patient. The "+21" denotes the additional chromosome 21 that is present, confirming the diagnosis of trisomy 21. The inclusion of "c[20]" in the notation "47,XY,+21c[20]" suggests that additional details about the abnormal chromosome might be provided; however, it is not standard for simply reporting trisomy 21 and could imply a different context, which is not applicable here for a straightforward case of Down syndrome. The nomenclature that is most commonly accepted and understood for this condition does not require additional specifications beyond the presence of the trisomy. In summary, the correct nomenclature accurately reflects the presence of the extra chromosome and the patient's sex, aligning with common cytogenetic reporting standards for Down syndrome.