Trisomy 21, mosaicism (mitotic nondisjunction)

This code represents Down syndrome that is characterized by the presence of at least two cell lines, one with the typical trisomy 21 and another with a normal diploid chromosome complement. This mosaicism arises from a mitotic nondisjunction event after fertilization. Patients with mosaic trisomy 21 often present with a milder phenotype compared to full trisomy 21.

Use this code when documentation specifically identifies mosaic trisomy 21 as the patient's diagnosis. This diagnosis is typically confirmed through cytogenetic analysis showing a mixed cell population. Clinical scenarios include initial diagnosis, ongoing management, or when genetic counseling indicates this specific chromosomal abnormality.

• Ensure documentation explicitly states "mosaicism" or "mitotic nondisjunction" in relation to Trisomy 21.
• Do not use this code for full Trisomy 21 (non-mosaic) or other forms of Down syndrome.
• Consider additional codes for associated congenital anomalies or intellectual disabilities.