2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 884. 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 the other POA exempt codes in Chromosomal abnormalities, not elsewhere classified (Q90-Q99).

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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q90.1: its own notes plus those printed at Q90, block Q90-Q99, and Chapter 17. A note printed at a category, block or chapter applies to every code under it.

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Block Q90-Q99 Chromosomal abnormalities, not elsewhere classified applies to 74 codes
  • mitochondrial metabolic disorders (E88.4-)
From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • inborn errors of metabolism (E70-E88)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Q90 Down syndrome applies to 4 codes
  • code(s) to identify any associated degree of intellectual disabilities (F70-F79)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From Q90 Down syndrome applies to 4 codes
  • associated physical condition(s), such as atrioventricular septal defect (Q21.2-)

Notes

General instructions on how these codes are used.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • Codes from this chapter are not for use on maternal records

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Q90.1, its category, or a range that includes it.

Excludes1 4

These codes carry an Excludes1 note naming Q90.1: they are not reported together with it, unless the two conditions are unrelated.

  • E25 Adrenogenital disorders
    chromosomal abnormalities (Q90-Q99) names Q90-Q99, which includes this code
  • Block Q50-Q56 Congenital malformations of genital organs
    syndromes associated with anomalies in the number and form of chromosomes (Q90-Q99) names Q90-Q99, which includes this code
  • Q92 Other trisomies and partial trisomies of the autosomes, not elsewhere classified
    trisomies of chromosomes 13, 18, 21 (Q90-Q91) names Q90-Q91, which includes this code
  • Z15 Genetic susceptibility to disease
    chromosomal anomalies (Q90-Q99) names Q90-Q99, which includes this code

Code First 1

These codes say to code first a condition named in the note, and Q90.1 is one of the conditions named.

  • D84.81 Immunodeficiency due to conditions classified elsewhere
    chromosomal abnormalities (Q90-Q99) names Q90-Q99, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Q90.1Overview

What is the ICD-10 code for trisomy 21, mosaicism (mitotic nondisjunction)?

The ICD-10-CM code for trisomy 21, mosaicism (mitotic nondisjunction) is Q90.1 (sometimes written as Q901). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

What MS-DRG does Q90.1 group to?

When trisomy 21, mosaicism (mitotic nondisjunction) is the principal diagnosis on an inpatient stay, it groups to MS-DRG 884 (organic Disturbances and Intellectual Disability), which carries a relative weight of 1.5998. Higher weights mean higher Medicare reimbursement.

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. The code appears in the Chromosomal abnormalities, not elsewhere classified (Q90-Q99) range of the CMS exempt list.

Does Q90.1 need an additional code?

When the condition applies, yes. The Use Additional Code note at Q90, which applies to Q90.1, reads: code(s) to identify any associated degree of intellectual disabilities (F70-F79). The additional code is reported after Q90.1.