Trisomy 21, nonmosaicism (meiotic nondisjunction)

This code represents the most common form of Down syndrome, characterized by the presence of an extra copy of chromosome 21 in all cells of the body, resulting from a meiotic nondisjunction event. Individuals with this condition typically exhibit a range of intellectual disabilities, characteristic facial features, and various congenital anomalies.

This code is used when documentation confirms a diagnosis of Trisomy 21, specifically the nonmosaic form, often identified through karyotyping. It applies to patients diagnosed with classic Down syndrome where all cells contain the extra chromosome 21, distinguishing it from mosaic forms.

• Ensure documentation explicitly states "nonmosaic" or "meiotic nondisjunction" to support this specific code.
• Do not use this code for mosaic Down syndrome or translocation Down syndrome; these have distinct codes.
• Always code any associated congenital anomalies or medical conditions (e.g., congenital heart defects, hypothyroidism) in addition to the Down syndrome diagnosis.