G40.844
BillableKCNQ2-related epilepsy, intractable, without status epilepticus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G40.844 an HCC code?
Yes. G40.844 maps to Seizure Disorders and Convulsions under the CMS-HCC V28 risk adjustment model (and Seizure Disorders and Convulsions 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 G40.844
For G40.844to 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 G40.844 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G40.844 is the ICD-10-CM diagnosis code for kcnq2-related epilepsy, intractable, without status epilepticus. Epilepsy caused by a KCNQ2 gene mutation that does not respond well to medication, not currently in a prolonged seizure state. G40.844 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering episodic and paroxysmal disorders (g40-g47).
Under the CMS-HCC V28 risk adjustment model, G40.844 maps to Seizure Disorders and Convulsions (HCC 201) with a community, non-dual, aged base RAF weight of 0.262. Under the older V24 model, G40.844 mapped to the same category but with a base RAF weight of 0.244 — V28 recalibrated weights across the entire model. 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.
Verify genetic testing results confirming KCNQ2 mutation are in the documentation. Because G40.844 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 G40.844 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify genetic testing results confirming KCNQ2 mutation are in the documentation
- •Document evidence of intractability with failed anti-seizure medication trials
Clinical Significance
KCNQ2-related epilepsy, intractable, without status epilepticus represents chronic drug-resistant KCNQ2 encephalopathy. These patients have severe variants of KCNQ2 mutations leading to ongoing seizures despite treatment, intellectual disability, and motor impairment. This is a lifelong condition requiring multidisciplinary management.
Documentation Requirements
- ✓Genetic confirmation of KCNQ2 mutation
- ✓Documentation of drug resistance with failed antiepileptic medication trials
- ✓Absence of status epilepticus at the encounter
- ✓Current seizure frequency and types
- ✓Developmental and cognitive assessments
- ✓Treatment plan including advanced therapy considerations
Commonly Confused Codes
- •G40.842 — KCNQ2 epilepsy, NOT intractable; seizures controlled
- •G40.843 — KCNQ2 epilepsy, intractable, WITH status epilepticus
- •G40.834 — Dravet syndrome, intractable; different genetic epilepsy
- •G40.804 — Other epilepsy, intractable; less specific when KCNQ2 is confirmed
- •G40.42 — CDKL5 Deficiency Disorder; different gene