What is the nomenclature for a patient with Down syndrome referred for a hematologic disorder where only trisomy 21 was found?

The correct nomenclature for a patient with Down syndrome who has been found to have trisomy 21 is 47,XY,+21c[20]. This terminology is used to indicate the total number of chromosomes present, the sex chromosomes, and the specific abnormality found.

In this case, the notation begins with "47," which indicates that the patient has a total of 47 chromosomes, one more than the typical diploid number of 46. The "XY" designation reveals that the individual is male. The "+21" specifies that there is an extra copy of chromosome 21 present, which is the defining characteristic of Down syndrome. The addition of "c[20]" can refer to a specific characteristic of the cells being evaluated, such as the number of metaphase cells counted or observed during the cytogenetic analysis.

Understanding this nomenclature is crucial since it succinctly communicates the genetic makeup of the patient, particularly relevant in a clinical setting such as assessing associated hematologic disorders, where the presence of the additional chromosome can significantly influence diagnosis and treatment.