2026 ICD-10-CM Diagnosis Code Q90.1Trisomy 21, mosaicism (mitotic nondisjunction)

ICD-10-CM Codes›Q00-Q99›Q90-Q99›Q90

ICD-10-CM Q90.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Q90.1 is a billable ICD-10-CM diagnosis code for trisomy 21, mosaicism (mitotic nondisjunction). It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is exempt from POA reporting. Coders also document this condition as complete trisomy 21 syndrome. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Chromosomal abnormalities.

Code Identity

ICD-10-CM Code
Q90.1
Billable Status
Yes — Valid for Submission
Code Describes
Trisomy 21, mosaicism (mitotic nondisjunction)
Short Description
Trisomy 21, mosaicism (mitotic nondisjunction)
Same as the full description in the CMS dataset.
Parent Code
Q90
Down syndrome

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ90-Q99Chromosomal abnormalities, not elsewhere classified
CategoryQ90Down syndrome
This CodeQ90.1Trisomy 21, mosaicism (mitotic nondisjunction)

Present on Admission (POA)Billing

Q90.1 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Complete trisomy 21 syndrome
  • Trisomy 21- mitotic nondisjunction mosaicism
  • Whole chromosome trisomy - mitotic nondisjunction mosaicism

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Down syndrome
      • mitotic nondisjunction
    • Down syndrome
      • mosaicism
    • Syndrome
      • trisomy
        • 21
          • mitotic nondisjunction
    • Syndrome
      • trisomy
        • 21
          • mosaicism
    • Trisomy(syndrome)
      • 21 (partial)
        • mitotic nondisjunction
    • Trisomy(syndrome)
      • 21 (partial)
        • mosaicism

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MAL009
Chromosomal abnormalities
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Down Syndrome

    a chromosome disorder associated either with an extra chromosome 21 or an effective trisomy for chromosome 21. clinical manifestations include hypotonia, short stature, brachycephaly, upslanting palpebral fissures, epicanthus, brushfield spots on the iris, protruding tongue, small ears, short, broad hands, fifth finger clinodactyly, single transverse palmar crease, and moderate to severe intellectual disability. cardiac and gastrointestinal malformations, a marked increase in the incidence of leukemia, and the early onset of alzheimer disease are also associated with this condition. pathologic features include the development of neurofibrillary tangles in neurons and the deposition of amyloid beta-protein, similar to the pathology of alzheimer disease. (menkes, textbook of child neurology, 5th ed, p213)

Patient EducationClinical

Down Syndrome

Down syndrome is a condition in which a person has an extra chromosome or an extra piece of a chromosome. This extra copy changes how a baby's body and brain develop. It can cause both mental and physical challenges during their lifetime.

The full article covers:

  • What is Down syndrome?
  • What causes Down syndrome?
  • What are the symptoms of Down syndrome?
  • What other problems does Down syndrome cause?
  • How is Down syndrome diagnosed?
  • What are the treatments for Down syndrome?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert Q90.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
758.0 Down's syndrome
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Q90.1Overview

Is Q90.1 (Down syndrome) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report trisomy 21, mosaicism (mitotic nondisjunction) on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is Q90.1 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for trisomy 21, mosaicism (mitotic nondisjunction) on inpatient claims.

What is the ICD-9 equivalent of Q90.1?

Under the General Equivalence Mappings, trisomy 21, mosaicism (mitotic nondisjunction) converts to ICD-9-CM 758.0 (Down's syndrome). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.