Marker chromosomes in abnormal individual

This code signifies the presence of one or more supernumerary, structurally abnormal chromosomes of unknown origin, often detected through cytogenetic analysis. These marker chromosomes are typically small and can be associated with a range of developmental abnormalities or intellectual disabilities, depending on their genetic content and mosaicism.

Assign this code when a patient's karyotype or other genetic testing reveals the presence of an unidentifiable, extra chromosome that is structurally abnormal. Documentation should clearly state "marker chromosome" or "supernumerary marker chromosome" in the context of an abnormal individual, often with associated clinical findings.

• Do not use this code for identified chromosomal abnormalities (e.g., specific trisomies, deletions, or translocations).
• Always sequence this code after any definitive clinical manifestation or congenital anomaly associated with the marker chromosome.
• Ensure the documentation specifies "abnormal individual" to differentiate from marker chromosomes found in phenotypically normal individuals (which would typically not be coded with this specific diagnosis).