G40.42
BillableCyclin-Dependent Kinase-Like 5 Deficiency Disorder
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G40.42 an HCC code?
Yes. G40.42 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 G40.42
For G40.42 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 G40.42 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G40.42 is the ICD-10-CM diagnosis code for cyclin-dependent kinase-like 5 deficiency disorder. A rare genetic disorder caused by mutations in the CDKL5 gene that causes severe, early-onset epilepsy often accompanied by developmental delays and other neurological problems. G40.42 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, G40.42 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, G40.42 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.
This is a specific genetic epilepsy syndrome; verify genetic testing confirmation in the medical record when possible. Because G40.42 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 G40.42 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a specific genetic epilepsy syndrome; verify genetic testing confirmation in the medical record when possible
- •This condition typically presents in infancy with infantile spasms and requires specialized neurological management
Clinical Significance
Cyclin-Dependent Kinase-Like 5 (CDKL5) Deficiency Disorder is a rare genetic epilepsy caused by mutations in the CDKL5 gene, presenting with severe early-onset seizures typically beginning in infancy. Patients experience multiple seizure types, profound developmental delays, and significant neurological impairment requiring comprehensive multidisciplinary care. This is a lifelong condition with substantial healthcare resource needs including specialized neurology, developmental pediatrics, and therapy services.
Documentation Requirements
- ✓Confirmed CDKL5 gene mutation through genetic testing results
- ✓Clinical diagnosis of CDKL5 Deficiency Disorder by a neurologist or geneticist
- ✓Documentation of seizure types and frequency
- ✓Developmental milestone assessment and delays
- ✓Current antiepileptic medication regimen
- ✓Associated comorbidities (cortical visual impairment, motor impairment, gastrointestinal issues)
Use Additional Code
Commonly Confused Codes
- •G40.411 — Other generalized epilepsy, intractable; use when CDKL5 mutation is NOT confirmed
- •G40.834 — Dravet syndrome; different genetic etiology (SCN1A mutation vs CDKL5)
- •G40.814 — Lennox-Gastaut syndrome; distinct EEG and clinical features
- •G40.824 — Epileptic spasms, intractable; CDKL5 may present with spasms but has its own specific code
- •F84.2 — Rett syndrome; historically overlapped with CDKL5 but now recognized as distinct conditions