Crystal's Coder Hub🧬 ICD-10-CM G11.3 — Cerebellar Ataxia With Defective DNA Repair
Billable Code Confirmed
ICD-10-CM G11.3 is a valid, billable 4-character diagnosis code. The first three characters (G11) specify hereditary ataxia, and the 4th character (3) specifically designates the variant associated with defective DNA repair. No additional characters are required.
Non-Billable Parent Codes — Never Submit These
- ❌
G11— 3-character header — Lacks specificity regarding the type or etiology of the hereditary ataxia.Always submit G11.3 (all 4 characters) when Ataxia telangiectasia or Louis-Bar syndrome is documented.
Clinical Context: Multisystem Involvement
While classified under diseases of the nervous system, G11.3 (Ataxia telangiectasia) is a complex multisystem disorder. Coders should thoroughly review the chart for associated immunodeficiencies, recurrent sinopulmonary infections, and neoplasms, which are hallmarks of the disease and require separate, additional coding.
Code Classification
ICD-10-CM Diagnosis Code — wRVU, assistant payable, and global period fields are not applicable. See CPT Procedural Crosswalk and ICD-10-PCS Crosswalk sections for associated procedural billing.
🔍 Code Description
ICD-10-CM G11.3 classifies Cerebellar ataxia with defective DNA repair, the most prominent form of which is Ataxia telangiectasia (Louis-Bar syndrome).
Pathophysiologically, this is an autosomal recessive disorder caused by mutations in the ATM (Ataxia Telangiectasia Mutated) gene. The ATM protein is responsible for coordinating the cellular response to DNA double-strand breaks. When defective, cells cannot repair DNA damage, leading to rapid cell death (especially in the cerebellum) and a high propensity for cancerous mutations.
Clinically, patients present in early childhood with progressive cerebellar ataxia (wobbly gait, poor coordination). By early elementary school, they develop characteristic “telangiectasias” (dilated, spider-like blood vessels) primarily on the conjunctiva/sclera of the eyes and sun-exposed skin. The DNA repair defect also severely impacts the immune system, leading to profound immunodeficiency, recurrent severe respiratory infections, and a highly elevated risk of leukemias and lymphomas.
🌳 Code Tree / Hierarchy
G11 Hereditary ataxia ❌ Non-billable
│
├── G11.0 Congenital nonprogressive ataxia ✅ Billable
├── G11.1- Early-onset cerebellar ataxia
├── G11.2 Late-onset cerebellar ataxia ✅ Billable
├── G11.3 Cerebellar ataxia with defective DNA repair ◀ THIS CODE ✅ Billable
├── G11.4 Hereditary spastic paraplegia ✅ Billable
├── G11.8 Other hereditary ataxias ✅ Billable
└── G11.9 Hereditary ataxia, unspecified ✅ Billable
Differentiating Early-Onset Ataxias
While Ataxia telangiectasia has an early onset (toddler years), it is specifically categorized under G11.3 due to the DNA repair defect, rather than the
G11.1-(Early-onset cerebellar ataxia) block which houses conditions like Friedreich’s ataxia.
✅ Includes
The following specific eponymous syndromes and clinical terms map directly to G11.3 when documented:
- Ataxia telangiectasia
- Louis-Bar syndrome
- Cerebellar ataxia with DNA repair defect
- ATM gene mutation causing ataxia
❌ Excludes
Excludes 2 — May Be Coded in Addition if Separately Present
| Code | Description | Note |
|---|---|---|
| G80.- | Cerebral palsy | Mutually exclusive by disease definition, but governed by Type 2 Excludes. CP is static, whereas G11.3 is progressive. |
| G60.- | Hereditary and idiopathic neuropathy | May be coded simultaneously if the patient has a distinct, separately identifiable peripheral neuropathy. |
| E70-E88 | Metabolic disorders | Can be coded concurrently if a distinct metabolic condition is present. |
Symptom Exclusions
According to ICD-10-CM symptom sequencing rules, if G11.3 is established, do NOT code
R27.0(Ataxia, unspecified). The definitive condition supersedes the symptom code.
📋 Clinical Overview
Common Diagnoses / Clinical Indications
Patients assigned this code typically present to multidisciplinary clinics (Neurology/Immunology) with:
- Progressive Cerebellar Ataxia: Beginning when the child learns to walk (toddler age).
- Oculocutaneous Telangiectasias: Spider veins appearing on the whites of the eyes and face (typically appearing between ages 3-5).
- Recurrent Infections: Severe sinopulmonary infections due to IgA, IgE, and IgG subclass deficiencies.
- Elevated AFP: Alpha-fetoprotein levels are uniquely and consistently elevated in the blood.
- Radiation Sensitivity: Extreme sensitivity to ionizing radiation (e.g., standard X-rays), which damages their already vulnerable DNA.
💰 HCC Risk Adjustment (CMS-HCC v28)
| Field | Detail |
|---|---|
| CMS-HCC Model Version | v28 (2024-2025 Implementation) |
| HCC Assignment | ✅ Mapped — HCC 72 |
| HCC Category | Spinal Cord Disorders |
G11.3 must be captured at least once every calendar year during a face-to-face encounter. Providers must document how the condition is being managed (MEAT criteria: Monitor, Evaluate, Assess, Treat) to ensure the HCC category applies.
Multiplying Risk with Associated Conditions
Because Ataxia telangiectasia involves profound immunodeficiency, look for and code associated immune defects (e.g.,
D80.1Nonfamilial hypogammaglobulinemia, orD82.8Immunodeficiency associated with other specified major defects) if documented by the provider, as these carry massive additional risk weights.
🏥 DRG Assignment
MDC 01 — Diseases and Disorders of the Nervous System
| DRG | Title | Est. Relative Weight* |
|---|---|---|
| DRG 058 | Multiple Sclerosis and Cerebellar Ataxia with MCC | ~2.05 |
| DRG 059 | Multiple Sclerosis and Cerebellar Ataxia with CC | ~1.15 |
| DRG 060 | Multiple Sclerosis and Cerebellar Ataxia without CC/MCC | ~0.85 |
Approximate. Verify against IPPS FY2026 Final Rule tables.
🛠️ Commonly Associated CPT Codes (Profee / Outpatient)
Procedure and Evaluation Context
Management of Louis-Bar syndrome is extremely complex, involving diagnostic imaging (cautiously, due to radiation risk), immunologic laboratory testing, and high-level evaluation and management.
| CPT Code | Description | Modifier Notes / wRVU |
|---|---|---|
| 99205 / 99215 | Office or other outpatient visit (High MDM) | Frequently utilized due to the high risk of morbidity, multisystem care coordination, and complex medical decision-making required. (wRVU: 3.16 / 2.80) |
| 70551 | Magnetic resonance (e.g., proton) imaging, brain; without contrast material | The preferred imaging modality (over CT) because MRIs do not use ionizing radiation, which is toxic to ATM patients. (wRVU: ~1.48 for modifier -26) |
| 82784 | Gammaglobulin (immunoglobulin); IgA, IgD, IgG, IgM, each | Used frequently to monitor the patient’s immunodeficiency status. Billed per immunoglobulin tested. |
| 82105 | Alpha-fetoprotein (AFP); serum | A key diagnostic biomarker consistently elevated in Ataxia telangiectasia. |
💊 Coding Scenarios and Examples
Scenario 1 — Pediatric Multidisciplinary Clinic
Clinical Vignette: A 6-year-old male with an established diagnosis of Ataxia telangiectasia presents to the immunology/neurology clinic for evaluation. The mother reports worsening ataxia, requiring a wheelchair for long distances. The physician notes extensive ocular telangiectasias. The patient has also had three severe sinus infections in the last 4 months. Labs show severely depressed IgA levels. The physician prescribes prophylactic antibiotics for the immunodeficiency and coordinates with physical therapy. High MDM.
Diagnoses:
- G11.3 — Cerebellar ataxia with defective DNA repair (Primary neurological/genetic disorder)
D80.2— Selective deficiency of immunoglobulin A [IgA] (Associated immunological manifestation)J32.9— Chronic sinusitis, unspecified (Resulting infection)Z99.3— Dependence on wheelchair (Status code)
Procedure:
- 99215 — E/M established patient, High MDM
Scenario 2 — CDI Query: Vague Ataxia Documentation
Clinical Vignette: A pediatric patient’s problem list includes “Louis-Bar syndrome,” but the attending physician’s progress note simply states, “Patient here for follow up of ataxia and recurrent pneumonia. Prescribing IVIG.”
Action / Outcome:
While “ataxia” defaults to R27.0, the presence of Louis-Bar syndrome on the problem list suggests a highly specific, high-risk systemic disease. Send a CDI query to the provider asking to confirm the definitive diagnosis underlying the ataxia and recurrent infections.
Query Response: “Patient has Ataxia telangiectasia.”
Corrected ICD-10-CM Coding:
- G11.3 — Cerebellar ataxia with defective DNA repair
J18.9— Pneumonia, unspecified organismD82.8— Immunodeficiency associated with other specified major defects (if linked by provider)
⚠️ Coding Pitfalls and Tips
| Pitfall or Tip | |
|---|---|
| ❌ | Using Symptom Codes Only. Coding R27.0 (Ataxia) or I78.0 (Hereditary hemorrhagic telangiectasia) separately instead of utilizing the specific combination code G11.3 for Ataxia telangiectasia results in severe loss of clinical specificity and HCC risk capture. |
| ❌ | Ignoring the Immune/Oncologic Risk. Failing to read the entire chart for associated immunodeficiencies or secondary malignancies. G11.3 covers the neurological/genetic component, but additional codes are required to capture immune system failures and cancers. |
| ✅ | Query for Eponyms. If the provider documents “Louis-Bar syndrome,” know that this maps directly to G11.3. Confirm with the provider if only symptoms are documented but the syndrome is known in the patient’s history. |
| ✅ | Capture Annually for HCC. The condition is permanent and progressive. It must be addressed, assessed, and coded at least once per calendar year in the outpatient setting to maintain accurate Medicare Advantage or ACA risk adjustment data.^4 |
📚 Sources
1. CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2025/FY2026. Section I.B.4: Signs and Symptoms.2. American Academy of Neurology (AAN). Consensus guidelines on the evaluation of pediatric ataxia.
3. Rothblum-Oviatt, C., et al. (2016). Ataxia telangiectasia: a review. Orphanet Journal of Rare Diseases, 11(1), 159. (Source for pathophysiology, clinical presentation, and multisystem involvement).
4. CMS. 2025-2026 Medicare Advantage Risk Adjustment — CMS-HCC Model v28 ICD-10-CM Mappings.
5. American Medical Association (AMA). CPT Professional Edition 2025. Evaluation and Management / Pathology and Laboratory Guidelines.