Whole chromosome monosomy, mosaic (mitotic nondisjunction)

This code describes a genetic condition where an individual has a missing entire chromosome in some, but not all, of their cells. This mosaicism typically arises from an error during cell division (mitotic nondisjunction) after fertilization, leading to two or more cell lines with different chromosomal complements. The clinical presentation varies widely depending on the specific chromosome involved and the proportion of affected cells.

Use this code when documentation specifies a diagnosis of whole chromosome monosomy that is present in a mosaic pattern. This diagnosis is typically confirmed through cytogenetic studies, such as karyotyping or FISH, showing both normal and monosomic cell lines. Documentation should clearly indicate "mosaicism" or "mitotic nondisjunction" as the cause.

• Do not use this code for complete (non-mosaic) monosomies of an entire chromosome; specific codes exist for those conditions (e.g., Turner syndrome for monosomy X).
• Ensure the documentation explicitly states "mosaicism" or describes varying cell lines; otherwise, a more specific code for a non-mosaic chromosomal abnormality might be appropriate.
• Sequence this code as a primary diagnosis when it is the reason for the encounter or as a secondary diagnosis when it contributes to the patient's overall health status.