What is ICD-10 code E79.2?

E79.2 is the ICD-10-CM diagnosis code for Myoadenylate deaminase deficiency. A rare genetic disorder affecting muscle metabolism that can cause muscle pain, weakness, and exercise intolerance. It belongs to the ICD-10-CM chapter for endocrine, nutritional and metabolic diseases (e00-e89). E79.2 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E79.2 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. E79.2 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. E79.2 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for E79.2?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. E79.2 was a payment HCC under V24 (Other Significant Endocrine and Metabolic Disorders) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting E79.2?

Document whether symptoms are present or if this is an incidental finding May be associated with myalgia or muscle weakness that should be coded separately Because E79.2 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.

E79.2: Myoadenylate deaminase deficiency — ICD-10 | Other Significant Endocrine and Metabolic

ICD-10-CM Code View

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Code lookupE79.2Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

E79.2

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

Myoadenylate deaminase deficiency

A rare genetic disorder affecting muscle metabolism that can cause muscle pain, weakness, and exercise intolerance.

Buddy Insight

Myoadenylate deaminase deficiency (MAD deficiency) is the most common metabolic myopathy, affecting approximately 2% of the population.

CMS-HCC V28

Not risk-adjusted for this model/period.

RAF 0

CMS-HCC V24

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.230

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.0

RXHCC

Mapped

HCC 43

Other Significant Endocrine a...

RAF 0.0

Code Trumping

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Code Book Path

Official

E79Disorders of purine and pyrimidine metabolism

E79.2Myoadenylate deaminase deficiency

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for E79.2 in this effective period.

Excludes 2

Official

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

Related Child Codes

Official

E79.0Hyperuricemia without signs of inflammatory arthritis and tophaceous disease

E79.1Lesch-Nyhan syndrome

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 E79.2 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 E79.2 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E79.2 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E79.2 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Provider diagnosis of myoadenylate deaminase deficiency

Confirmatory testing: muscle biopsy with histochemical staining showing absent MAD activity, or AMPD1 gene mutation

Forearm ischemic exercise test results if performed (absence of ammonia rise)

Symptom documentation: exercise intolerance, myalgia, cramping, early fatigue

MEAT Support

HCC Buddy guidance

Provider diagnosis of myoadenylate deaminase deficiency

Confirmatory testing: muscle biopsy with histochemical staining showing absent MAD activity, or AMPD1 gene mutation

Forearm ischemic exercise test results if performed (absence of ammonia rise)

Symptom documentation: exercise intolerance, myalgia, cramping, early fatigue

Audit Caution

HCC Buddy guidance

Coding only the symptom (myalgia, exercise intolerance) without the underlying metabolic diagnosis

Not recognizing that many asymptomatic carriers exist — only code when clinically significant

Confusing MAD deficiency with McArdle disease (glycogen storage disease type V) which also causes exercise intolerance

Using a general myopathy code when the specific metabolic deficiency has been confirmed

Common Mistakes

HCC Buddy guidance

G72.9 — Myopathy, unspecified: MAD deficiency is a specific metabolic myopathy, not an unspecified one

M79.1 — Myalgia: symptom code only; use E79.2 for the underlying metabolic cause

E79.89 — Other disorders of purine and pyrimidine metabolism: for purine disorders that are not specifically MAD deficiency

G71.14 — Myotonic dystrophy: different myopathy that may cause similar exercise intolerance

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is E79.2 an HCC code?

Yes. E79.2 maps to Other Significant Endocrine and Metabolic Disorders under the V24 model but is not retained in V28.

HCC Category Mapping

V24HCC 23, Other Significant Endocrine and Metabolic Disorders

0.230

ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders

0.000

RxHCCHCC 43, Other Significant Endocrine and Metabolic Disorders

0.000

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.

Work E79.2 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for E79.2

For E79.2to 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 E79.2 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E79.2 is the ICD-10-CM diagnosis code for myoadenylate deaminase deficiency. A rare genetic disorder affecting muscle metabolism that can cause muscle pain, weakness, and exercise intolerance. E79.2 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 older CMS-HCC V24 model, E79.2 maps to Other Significant Endocrine and Metabolic Disorders (HCC 23) with a community, non-dual, aged base RAF weight of 0.230. 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.

Document whether symptoms are present or if this is an incidental finding. Because E79.2 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 E79.2 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Document whether symptoms are present or if this is an incidental finding
•May be associated with myalgia or muscle weakness that should be coded separately

Clinical Significance

Myoadenylate deaminase deficiency (MAD deficiency) is the most common metabolic myopathy, affecting approximately 2% of the population. While many carriers are asymptomatic, affected individuals experience exercise-induced muscle pain, cramping, and early fatigue due to impaired purine nucleotide cycling in skeletal muscle.

Documentation Requirements

✓Provider diagnosis of myoadenylate deaminase deficiency
✓Confirmatory testing: muscle biopsy with histochemical staining showing absent MAD activity, or AMPD1 gene mutation
✓Forearm ischemic exercise test results if performed (absence of ammonia rise)
✓Symptom documentation: exercise intolerance, myalgia, cramping, early fatigue
✓Exclusion of other myopathies
✓Activity modification plan and symptom management

Commonly Confused Codes

•G72.9: Myopathy, unspecified: MAD deficiency is a specific metabolic myopathy, not an unspecified one
•M79.1: Myalgia: symptom code only; use E79.2 for the underlying metabolic cause
•E79.89: Other disorders of purine and pyrimidine metabolism: for purine disorders that are not specifically MAD deficiency
•G71.14: Myotonic dystrophy: different myopathy that may cause similar exercise intolerance