2027 ICD-10-CM Diagnosis Code Q99.2Fragile X chromosome

ICD-10-CM Codes›Q00-Q99›Q90-Q99›Q99

ICD-10-CM Q99.2
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Q99.2 is a billable ICD-10-CM diagnosis code for fragile X chromosome. 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 dementia due to chromosomal anomaly. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Chromosomal abnormalities.

Q99.2 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 148 for payment year 2027.

Code Identity

ICD-10-CM Code
Q99.2
Billable Status
Yes — Valid for Submission
Code Describes
Fragile X chromosome
Short Description
Fragile X chromosome
Same as the full description in the CMS dataset.
Parent Code
Q99
Other chromosome abnormalities, not elsewhere classified

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ90-Q99Chromosomal abnormalities, not elsewhere classified
CategoryQ99Other chromosome abnormalities, not elsewhere classified
This CodeQ99.2Fragile X chromosome

Present on Admission (POA)Billing

Q99.2 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).

Medicare Risk Adjustment (HCC)Billing

Q99.2 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model, but it maps to payment categories in the other CMS models shown below.

CMS-HCC V28 (Medicare Advantage Payment Model)
Not mapped
no payment category in the model that pays 100% of MA risk scores
Prior Model (CMS-HCC V24)
Not mapped under V24
this diagnosis newly risk-adjusts under the V28 model
Part D (RxHCC)
RxHCC 148 — Mild or Unspecified Intellectual Disability/Developmental Disorder
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Dementia due to chromosomal anomaly
  • Dementia due to fragile X syndrome
  • Dementia due to genetic disease
  • Fragile X associated primary ovarian insufficiency
  • Fragile X associated tremor ataxia syndrome
  • Fragile X chromosome
  • Fragile X syndrome
  • FRAXE intellectual disability syndrome
  • FRAXF syndrome
  • Premature ovarian insufficiency

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q99.2: its own notes plus those printed at block Q90-Q99 and Chapter 17. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Fragile X syndrome

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)

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 Q99.2, its category, or a range that includes it.

Excludes1 4

These codes carry an Excludes1 note naming Q99.2: 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
  • Q56 Indeterminate sex and pseudohermaphroditism
    pseudohermaphroditism with specified chromosomal anomaly (Q96-Q99) names Q96-Q99, 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 Q99.2 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

Patient EducationClinical

Fragile X Syndrome

Fragile X syndrome is the most common form of inherited developmental disability. A problem with a specific gene causes the disease. Normally, the gene makes a protein you need for brain development. But the problem causes a person to make little or none of the protein. This causes the symptoms of Fragile X.

Read the full article at MedlinePlus

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

Convert Q99.2 to ICD-9-CMHistory

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

ICD-9-CM
759.83 Fragile x syndrome
Exact Match The mapping is direct, with no qualifiers.

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 Q99.2Overview

What is the ICD-10 code for fragile X chromosome?

The ICD-10-CM code for fragile X chromosome is Q99.2 (sometimes written as Q992). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is Q99.2 (Other chromosome abnormalities, not elsewhere classified) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report fragile X chromosome on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does Q99.2 group to?

When fragile X chromosome 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 Q99.2 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 fragile X chromosome on inpatient claims. The code appears in the Chromosomal abnormalities, not elsewhere classified (Q90-Q99) range of the CMS exempt list.

What is the ICD-9 equivalent of Q99.2?

Under the General Equivalence Mappings, fragile X chromosome converts to ICD-9-CM 759.83 (fragile x syndrome). The mapping is a direct match.

Does Q99.2 risk-adjust for Medicare Advantage payment?

Not for Medicare Advantage: Q99.2 maps to no category in the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 148 (Mild or Unspecified Intellectual Disability/Developmental Disorder).