G11.5
BillableHypomyelination - hypogonadotropic hypogonadism - hypodontia
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G11.5 an HCC code?
Yes. G11.5 maps to Cerebellar Ataxia and Other Degenerative Diseases of Nervous System under the CMS-HCC V28 risk adjustment model (and Spinal Cord Disorders/Injuries under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
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.
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 Cerebellar Ataxia and Other Degenerative Diseases of Nervous System (HCC 200) with a community, non-dual, aged base RAF weight of 0.262. Under the older CMS-HCC V24 model, G11.5 maps to Spinal Cord Disorders/Injuries (HCC 72) with a community, non-dual, aged base RAF weight of 0.464. 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.
Code each component of the syndrome separately if they are clinically significant and documented. Because G11.5 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, 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