Yes. G11.5 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. G11.5 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does G11.5 map to under V28?

G11.5 maps to CMS-HCC V28 HCC 200 (Friedreich and Other Hereditary Ataxias; Huntington Disease). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM G11.5: Hypomyelination

G11.5 maps to CMS-HCC V28 200. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

ICD-10-CM Code View

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Code lookupG11.5Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Systemic atrophies primarily affecting the central nervous system (G10-G14)

G11.5

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Hypomyelination - hypogonadotropic hypogonadism - hypodontia

Hypomyelination-hypogonadotropic hypogonadism-hypodontia is a rare genetic syndrome characterized by underdeveloped nerve insulation, hormone deficiency, and missing or underdeveloped teeth.

Buddy Insight

Hypomyelination-hypogonadotropic hypogonadism-hypodontia (4H syndrome) is an extremely rare genetic leukodystrophy affecting white matter formation, hormonal function, and dental development.

CMS-HCC V28

Mapped

HCC 200

Friedreich and Other Heredita...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 119

HHS-HCC 119 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 72

Spinal Cord Disorders/Injuries

Code-level coefficient reference

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

G11Hereditary ataxia

G11.5Hypomyelination - hypogonadotropic hypogonadism - hypodontia

Inclusion Terms

Official

4H syndrome
Pol III-related leukodystrophy

Excludes 2

Official

cerebral palsy (G80.-)
hereditary and idiopathic neuropathy (G60.-)
metabolic disorders (E70-E88)

Related Child Codes

Official

G11.0Congenital nonprogressive ataxia

G11.1Early-onset cerebellar ataxia

G11.2Late-onset cerebellar ataxia

G11.3Cerebellar ataxia with defective DNA repair

G11.4Hereditary spastic paraplegia

Includes

Official

ICD-10-CM does not list Includes notes for G11.5 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for G11.5 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for G11.5 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for G11.5 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for G11.5 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Brain MRI demonstrating hypomyelination pattern

Endocrine evaluation documenting hypogonadotropic hypogonadism

Dental examination documenting hypodontia (missing or underdeveloped teeth)

Genetic testing results (POLR3A or POLR3B mutations) if available

MEAT Support

HCC Buddy guidance

Brain MRI demonstrating hypomyelination pattern

Endocrine evaluation documenting hypogonadotropic hypogonadism

Dental examination documenting hypodontia (missing or underdeveloped teeth)

Genetic testing results (POLR3A or POLR3B mutations) if available

Audit Caution

HCC Buddy guidance

Coding only one component of the syndrome instead of using the specific combination code G11.5

Failing to code associated endocrine or dental conditions separately when they require independent management

Confusing this with other leukodystrophies that have different MRI and clinical patterns

Not documenting all three components of the syndrome to support the specific code

Common Mistakes

HCC Buddy guidance

G11.6 — Leukodystrophy with vanishing white matter disease: different leukodystrophy with distinct MRI pattern

E23.0 — Hypopituitarism: captures the hypogonadotropic component but misses neurological features

G11.8 — Other hereditary ataxias: less specific and should not be used when 4H syndrome is confirmed

E75.25 — Metachromatic leukodystrophy: different type of leukodystrophy with different clinical features

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is G11.5 an HCC code?

Yes. G11.5 (Hypomyelination - hypogonadotropic hypogonadism - hypodontia) maps to HCC 200, Friedreich and Other Hereditary Ataxias; Huntington Disease under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.279. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: G11.5 is billable and maps to V28 HCC 200, Friedreich and Other Hereditary Ataxias; Huntington Disease. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: G11.5
Description: Hypomyelination - hypogonadotropic hypogonadism - hypodontia
HCC (V28): HCC 200 — Friedreich and Other Hereditary Ataxias; Huntington Disease
RAF reference coefficient: 0.279
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 200, Friedreich and Other Hereditary Ataxias; Huntington Disease

0.279

ESRDHCC 72, Spinal Cord Disorders/Injuries

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work G11.5 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for G11.5

For G11.5 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed G11.5 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

G11.5 is the ICD-10-CM diagnosis code for hypomyelination - hypogonadotropic hypogonadism - hypodontia. Hypomyelination-hypogonadotropic hypogonadism-hypodontia is a rare genetic syndrome characterized by underdeveloped nerve insulation, hormone deficiency, and missing or underdeveloped teeth. G11.5 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering systemic atrophies primarily affecting the central nervous system (g10-g14).

Under the CMS-HCC V28 risk adjustment model, G11.5 maps to Friedreich and Other Hereditary Ataxias; Huntington Disease (HCC 200) with a source-labeled community, non-dual, aged reference coefficient of 0.279. No V24 mapping is shown for G11.5; use the applicable model and payment year when reviewing the V28 mapping. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Code each component of the syndrome separately if they are clinically significant and documented. Because G11.5 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for G11.5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Code each component of the syndrome separately if they are clinically significant and documented
•Document any associated neurological symptoms or developmental delays

Clinical Significance

Hypomyelination-hypogonadotropic hypogonadism-hypodontia (4H syndrome) is an extremely rare genetic leukodystrophy affecting white matter formation, hormonal function, and dental development. This multisystem condition requires coordination across neurology, endocrinology, and dentistry, representing substantial complexity and cost in patient management.

Documentation Requirements

✓Brain MRI demonstrating hypomyelination pattern
✓Endocrine evaluation documenting hypogonadotropic hypogonadism
✓Dental examination documenting hypodontia (missing or underdeveloped teeth)
✓Genetic testing results (POLR3A or POLR3B mutations) if available
✓Neurological examination documenting cerebellar signs and motor dysfunction
✓Developmental history and current functional status

Commonly Confused Codes

•G11.6: Leukodystrophy with vanishing white matter disease: different leukodystrophy with distinct MRI pattern
•E23.0: Hypopituitarism: captures the hypogonadotropic component but misses neurological features
•G11.8: Other hereditary ataxias: less specific and should not be used when 4H syndrome is confirmed
•E75.25: Metachromatic leukodystrophy: different type of leukodystrophy with different clinical features