G12.1
BillableOther inherited spinal muscular atrophy
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G12.1 an HCC code?
Yes. G12.1 maps to Motor Neuron Disease, Including Amyotrophic Lateral Sclerosis 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 G12.1
For G12.1 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 G12.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G12.1 is the ICD-10-CM diagnosis code for other inherited spinal muscular atrophy. Inherited forms of spinal muscular atrophy other than the infantile type, causing progressive muscle weakness and wasting. G12.1 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, G12.1 maps to Motor Neuron Disease, Including Amyotrophic Lateral Sclerosis (HCC 190) with a community, non-dual, aged base RAF weight of 0.935. Under the older CMS-HCC V24 model, G12.1 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.
Differentiate from G12.0 by confirming the patient does not have infantile-onset type I SMA. Because G12.1 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 G12.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Differentiate from G12.0 by confirming the patient does not have infantile-onset type I SMA
- •Document the specific type (juvenile, adult-onset, etc.) when available to support medical necessity
Clinical Significance
Other inherited spinal muscular atrophy encompasses types II (intermediate), III (Kugelberg-Welander), and IV (adult-onset), which present later and progress more slowly than type I. These conditions still cause significant disability and drive high costs, particularly with the availability of disease-modifying gene therapies that can cost hundreds of thousands of dollars annually.
Documentation Requirements
- ✓SMN1 gene deletion testing confirming spinal muscular atrophy diagnosis
- ✓Documentation of specific type (II, III, or IV) with age of onset
- ✓Current motor function status (ability to sit, stand, walk)
- ✓Respiratory function assessment
- ✓Disease-modifying therapy if applicable (nusinersen, risdiplam)
- ✓Confirmation that the patient does not have type I infantile form