2027 ICD-10-CM Diagnosis Code G11.9Hereditary ataxia, unspecified
ICD-10-CM Codes›G00–G99›G10-G14›G11
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 200
- Chronic Condition
G11.9 is a billable ICD-10-CM diagnosis code for hereditary ataxia, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 58 through 60. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 11 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other nervous system disorders (often hereditary or degenerative).
For Medicare Advantage risk adjustment, G11.9 maps to CMS-HCC Category 200 (Friedreich and Other Hereditary Ataxias; Huntington Disease) under the V28 model, adding a risk factor of about 0.279 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
G11.9 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
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.
- Ataxia due to mitochondrial mutations
- Ataxia with deafness and intellectual disability syndrome
- Ataxia with tapetoretinal degeneration syndrome
- Autosomal dominant cerebellar ataxia, deafness and narcolepsy syndrome
- Autosomal recessive ataxia due to ubiquinone deficiency
- Autosomal recessive cerebellar ataxia due to STUB1 deficiency
- Autosomal recessive cerebellar ataxia with oculomotor apraxia type 1
- Autosomal recessive cerebellar ataxia with oculomotor apraxia type 2
- Autosomal recessive cerebellar ataxia, epilepsy, intellectual disability syndrome due to RUBCN deficiency
- Autosomal recessive cerebellar ataxia, epilepsy, intellectual disability syndrome due to TUD deficiency
- Boucher Neuhäuser syndrome
- Cerebellar ataxia
- Cerebellar ataxia and ectodermal dysplasia
- Cerebellar ataxia associated with another disorder
- Cerebellar ataxia with oculomotor apraxia type 4
- Cerebellar ataxia, areflexia, pes cavus, optic atrophy, sensorineural hearing loss syndrome
- Cerebral ataxia
- Chorea due to hereditary ataxia
- Choreoathetosis
- Congenital cataract with ataxia and deafness syndrome
- Cutaneous syndrome with ichthyosis
- Early-onset progressive neurodegeneration, blindness, ataxia, spasticity syndrome
- Episodic ataxia
- Episodic ataxia type 7
- Fragile X associated tremor ataxia syndrome
- Gemignani syndrome
- Hereditary ataxia
- Hereditary cerebellar atrophy
- Hereditary cerebellar degeneration
- Hereditary choroidal dystrophy
- Ichthyosis, cerebellar degeneration and hepatosplenomegaly
- Infantile cerebellar and retinal degeneration
- Myoclonus, cerebellar ataxia, deafness syndrome
- Narcolepsy
- Neurodevelopmental delay, hypotonia, cerebellar ataxia, cardiac conduction defects syndrome
- Non-progressive cerebellar ataxia
- Optic atrophy, ataxia, peripheral neuropathy, global developmental delay syndrome
- Paroxysmal choreoathetosis
- Paroxysmal dystonia
- Paroxysmal dystonic choreoathetosis with episodic ataxia and spasticity
- Posthemiplegic ataxia
- Primary cerebellar degeneration
- Primary progressive cerebellar degeneration
- Progressive cerebellar ataxia
- PUM1-associated developmental disability, ataxia, seizure syndrome
- Retinal pigment epithelial dystrophy
- Retinitis pigmentosa-deafness syndrome
- Retinitis pigmentosa-deafness-ataxia syndrome
- Saldino-Mainzer dysplasia
- Seizure, sensorineural deafness, ataxia, intellectual disability, electrolyte imbalance syndrome
- Spinocerebellar disease
- X-linked progressive cerebellar ataxia
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to G11.9: its own notes plus those printed at G11 and Chapter 6. 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.
- Hereditary cerebellar ataxia NOS
- Hereditary cerebellar degeneration
- Hereditary cerebellar disease
- Hereditary cerebellar 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.
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name G11.9, its category, or a range that includes it.
Excludes1 2
These codes carry an Excludes1 note naming G11.9: they are not reported together with it, unless the two conditions are unrelated.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
brain (hereditary) G11.9
cerebellar (hereditary) G11.9
cerebral (hereditary) G11.9
hereditary G11.9
Disease, diseased See Also: Syndrome;
Syndrome See Also: Disease;
hereditary G11.9
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Hereditary Cerebellar Ataxia
cerebellar ataxia that is transmitted from parent to child.
Patient EducationClinical
Cerebellar Disorders
When you play the piano or hit a tennis ball you are activating the cerebellum. The cerebellum is the area of the brain that controls coordination and balance. Problems with the cerebellum include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert G11.9 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About G11.9Overview
What is the ICD-10 code for hereditary ataxia, unspecified?
The ICD-10-CM code for hereditary ataxia, unspecified is G11.9 (sometimes written as G119). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is G11.9 (Hereditary ataxia) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report hereditary ataxia, unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does G11.9 group to?
When hereditary ataxia, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 60, 58, 59, with relative weights from 0.9248 to 1.8430 depending on complications. Higher weights mean higher Medicare reimbursement.
Is G11.9 a CC or MCC?
CMS lists G11.9 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 11 closely related codes in its exclusion list.
What is the ICD-9 equivalent of G11.9?
Under the General Equivalence Mappings, hereditary ataxia, unspecified converts to ICD-9-CM 334.9 (spinocerebellar dis NOS). The mapping is approximate, so confirm the match fits the documentation.
What HCC is G11.9?
G11.9 (hereditary ataxia, unspecified) maps to CMS-HCC Category 200 (Friedreich and Other Hereditary Ataxias; Huntington Disease), commonly written as HCC 200, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 72 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does G11.9 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, G11.9 adds a risk adjustment factor of about 0.279 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.000 to 0.428 depending on the payment segment). HCC 200 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 200 category page.
