ICD-10-CM 2027
ICD-10 code for mosaicism down syndrome
From the official ICD-10-CM alphabetic index entry “Down syndrome › mosaicism”. Page updated September 29, 2026.
About coding mosaicism down syndrome
The ICD-10-CM code for mosaicism down syndrome is Q90.1 (Trisomy 21, mosaicism (mitotic nondisjunction)).
Within Q90 (down syndrome), Q90.1 is specifically for trisomy 21, mosaicism (mitotic nondisjunction). Related codes cover trisomy 21, nonmosaicism (meiotic nondisjunction) (Q90.0), trisomy 21, translocation (Q90.2) and unspecified (Q90.9).
Use an additional code(s) to identify any associated degree of intellectual disabilities (F70-F79).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
Common questions about mosaicism down syndrome ICD-10 codes
What is the ICD-10 code for mosaicism down syndrome?
- Q90.1 — Trisomy 21, mosaicism (mitotic nondisjunction).
Is Q90.1 billable?
- Yes. Q90.1 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can Q90.1 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict Q90.1 as a principal diagnosis.
Is Q90.1 a CC or MCC?
- No. Q90.1 is neither a CC nor an MCC under MS-DRG v44.0.