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E79.1 ICD-10-CM Code: Lesch-Nyhan syndrome

E79.1 maps to CMS-HCC V28 50 (RAF 0.648). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC Buddy coding tools

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FY 2026 Apr update / Endocrine, nutritional and metabolic diseases (E00-E89) / Metabolic disorders (E70-E88)

E79.1

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

Lesch-Nyhan syndrome

A rare inherited metabolic disorder affecting purine metabolism, causing intellectual disability, movement problems, and kidney issues.

Buddy the Bee presenting code insight

Buddy Insight

Lesch-Nyhan syndrome is a rare X-linked recessive disorder caused by complete deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT/HPRT), resulting in overproduction of uric acid.

CMS-HCC V28

HCC 50

RAF 0.648

CMS-HCC V24

HCC 23

RAF 0.194

ACA/HHS

HCC 29

Varies by metal level

ESRD/PACE

HCC 23

RAF 0.036

RXHCC

HCC 43

RAF 0.063

Code Book Path

Official
E79Disorders of purine and pyrimidine metabolism
E79.1Lesch-Nyhan syndrome

Inclusion Terms

Official
  • HGPRT deficiency

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E79.1 in this effective period.

Related Child Codes

Official
E79.0Hyperuricemia without signs of inflammatory arthritis and tophaceous disease
E79.2Myoadenylate deaminase deficiency
E79.8Other disorders of purine and pyrimidine metabolism
E79.9Disorder of purine and pyrimidine metabolism, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for E79.1 in this effective period.

Excludes 1

Official
  • Ataxia-telangiectasia (Q87.19)
  • Bloom's syndrome (Q82.8)
  • Cockayne's syndrome (Q87.19)
  • calculus of kidney (N20.0)
  • combined immunodeficiency disorders (D81.-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E79.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E79.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E79.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Provider diagnosis of Lesch-Nyhan syndrome
Confirmatory testing: HPRT enzyme assay showing absent or near-absent activity, or HPRT1 gene mutation
Neurological manifestations: self-injurious behavior, dystonia, choreoathetosis, intellectual disability
Uric acid levels and history of gout, nephrolithiasis, or renal complications

MEAT Support

HCC Buddy guidance
Provider diagnosis of Lesch-Nyhan syndrome
Confirmatory testing: HPRT enzyme assay showing absent or near-absent activity, or HPRT1 gene mutation
Neurological manifestations: self-injurious behavior, dystonia, choreoathetosis, intellectual disability
Uric acid levels and history of gout, nephrolithiasis, or renal complications

Audit Caution

HCC Buddy guidance
Coding only the hyperuricemia or gout without recognizing the underlying Lesch-Nyhan syndrome
Confusing partial HPRT deficiency (Kelley-Seegmiller syndrome, coded E79.89) with complete deficiency (Lesch-Nyhan)
Failing to code the neurological and behavioral manifestations as additional diagnoses
Not recognizing the X-linked inheritance pattern which exclusively affects males

Common Mistakes

HCC Buddy guidance
E79.0 — Hyperuricemia without gout: partial HPRT deficiency causes hyperuricemia without the neurological features of Lesch-Nyhan
M10.9 — Gout, unspecified: gout is a feature of Lesch-Nyhan but does not capture the full syndrome
E79.89 — Other disorders of purine and pyrimidine metabolism: for purine disorders that are NOT Lesch-Nyhan
F63.3 — Trichotillomania: self-injurious behavior may be confused with other behavioral disorders

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 E79.1 an HCC code?

Yes. E79.1 (Lesch-Nyhan syndrome) maps to Amyloidosis, Porphyria, and Other Specified Metabolic Disorders under the CMS-HCC V28 risk adjustment model (and Other Significant Endocrine and Metabolic Disorders under V24), with a community non-dual aged RAF of 0.648. It is billable for payment year 2026.

Coder answer: E79.1 is billable and maps to V28 HCC 50, Amyloidosis, Porphyria, and Other Specified Metabolic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
E79.1
Description
Lesch-Nyhan syndrome
HCC (V28)
HCC 50 — Amyloidosis, Porphyria, and Other Specified Metabolic Disorders
RAF
0.648
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 50, Amyloidosis, Porphyria, and Other Specified Metabolic Disorders
0.648
V24HCC 23, Other Significant Endocrine and Metabolic Disorders
0.194
ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders
0.036
RxHCCHCC 43, Other Significant Endocrine and Metabolic Disorders
0.063

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work E79.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for E79.1

For E79.1 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 E79.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E79.1 is the ICD-10-CM diagnosis code for lesch-nyhan syndrome. A rare inherited metabolic disorder affecting purine metabolism, causing intellectual disability, movement problems, and kidney issues. E79.1 sits in the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89), within the section covering metabolic disorders (e70-e88).

Under the CMS-HCC V28 risk adjustment model, E79.1 maps to Amyloidosis, Porphyria, and Other Specified Metabolic Disorders (HCC 50) with a community, non-dual, aged base RAF weight of 0.648. Under the older CMS-HCC V24 model, E79.1 maps to Other Significant Endocrine and Metabolic Disorders (HCC 23) with a community, non-dual, aged base RAF weight of 0.194. 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 genetic condition requiring documentation of diagnosis confirmation. Because E79.1 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 E79.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •This is a genetic condition requiring documentation of diagnosis confirmation
  • •Often associated with self-injurious behavior and neurological complications that should be coded separately

Clinical Significance

Lesch-Nyhan syndrome is a rare X-linked recessive disorder caused by complete deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT/HPRT), resulting in overproduction of uric acid. It is characterized by severe neurological impairment including compulsive self-injurious behavior (lip and finger biting), dystonia, intellectual disability, and gout, representing one of the most clinically distinctive metabolic disorders.

Documentation Requirements

  • ✓Provider diagnosis of Lesch-Nyhan syndrome
  • ✓Confirmatory testing: HPRT enzyme assay showing absent or near-absent activity, or HPRT1 gene mutation
  • ✓Neurological manifestations: self-injurious behavior, dystonia, choreoathetosis, intellectual disability
  • ✓Uric acid levels and history of gout, nephrolithiasis, or renal complications
  • ✓Behavioral management plan for self-injury (restraints, dental guards, behavioral interventions)
  • ✓Medications: allopurinol for hyperuricemia, other supportive therapies

Commonly Confused Codes

  • •E79.0: Hyperuricemia without gout: partial HPRT deficiency causes hyperuricemia without the neurological features of Lesch-Nyhan
  • •M10.9: Gout, unspecified: gout is a feature of Lesch-Nyhan but does not capture the full syndrome
  • •E79.89: Other disorders of purine and pyrimidine metabolism: for purine disorders that are NOT Lesch-Nyhan
  • •F63.3: Trichotillomania: self-injurious behavior may be confused with other behavioral disorders

Child Codes

E79.0Hyperuricemia without signs of inflammatory arthritis and tophaceous disease
E79.1Lesch-Nyhan syndrome
HCC 50
E79.2Myoadenylate deaminase deficiency
E79.8Other disorders of purine and pyrimidine metabolism
E79.9Disorder of purine and pyrimidine metabolism, unspecified

Code Hierarchy

└E79Disorders of purine and pyrimidine metabolism└E79.1Lesch-Nyhan syndrome
└E79.1Lesch-Nyhan syndrome

Because E79.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

E79.1 maps to CMS-HCC V28 category 50, Amyloidosis, Porphyria, and Other Specified Metabolic Disorders. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because E79.1 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

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Open E79.1 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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