What is ICD-10 code E77.0?

E77.0 is the ICD-10-CM diagnosis code for Defects in post-translational modification of lysosomal enzymes. A rare genetic disorder affecting how the body modifies and processes lysosomal enzymes, which are proteins that break down waste materials in cells. E77.0 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E77.0 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. E77.0 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. E77.0 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 E77.0?

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. E77.0 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 E77.0?

This code requires documentation of the specific enzyme defect when available Often associated with lysosomal storage diseases; review clinical findings for more specific diagnosis Because E77.0 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.

2026 ICD-10-CM E77.0: Defects in post-translational

ICD-10-CM Code View

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Code lookupE77.0Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

E77.0

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

Defects in post-translational modification of lysosomal enzymes

A rare genetic disorder affecting how the body modifies and processes lysosomal enzymes, which are proteins that break down waste materials in cells.

Buddy Insight

CMS-HCC V28

N/A

—

Not risk-adjusted for this model/period.

Not mapped

CMS-HCC V24

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.194

ACA/HHS

Mapped

HCC 27

HHS-HCC 27

Varies by metal level

ESRD/PACE

Mapped

HCC 23

Other Significant Endocrine a...

RAF 0.036

RXHCC

Mapped

HCC 41

Lysosomal Storage Disorders

RAF 3.081

Code Book Path

Official

E77Disorders of glycoprotein metabolism

E77.0Defects in post-translational modification of lysosomal enzymes

Inclusion Terms

Official

Mucolipidosis II [I-cell disease]
Mucolipidosis III [pseudo-Hurler polydystrophy]

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E77.0 in this effective period.

Related Child Codes

Official

E77.1Defects in glycoprotein degradation

E77.8Other disorders of glycoprotein metabolism

E77.9Disorder of glycoprotein metabolism, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for E77.0 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for E77.0 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E77.0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E77.0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E77.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Specific disorder documented: mucolipidosis II (I-cell disease) or mucolipidosis III (pseudo-Hurler polydystrophy)

Confirmatory testing: elevated serum lysosomal enzyme levels, decreased intracellular enzyme activity, or GNPTAB/GNPTG gene mutations

Clinical manifestations: skeletal abnormalities, coarse features, developmental delay, cardiac involvement

Differentiation from MPS documented (different enzyme trafficking defect mechanism)

MEAT Support

HCC Buddy guidance

Specific disorder documented: mucolipidosis II (I-cell disease) or mucolipidosis III (pseudo-Hurler polydystrophy)

Confirmatory testing: elevated serum lysosomal enzyme levels, decreased intracellular enzyme activity, or GNPTAB/GNPTG gene mutations

Clinical manifestations: skeletal abnormalities, coarse features, developmental delay, cardiac involvement

Differentiation from MPS documented (different enzyme trafficking defect mechanism)

Audit Caution

HCC Buddy guidance

Misclassifying mucolipidosis as a mucopolysaccharidosis due to overlapping clinical features

Not recognizing 'I-cell disease' as mucolipidosis II, which should be coded to E77.0

Confusing post-translational modification defects (E77.0) with glycoprotein degradation defects (E77.1)

Failing to code manifestations like cardiac valve disease and skeletal abnormalities separately

Common Mistakes

HCC Buddy guidance

E76.01 — Hurler syndrome: similar clinical features but different pathophysiology (direct enzyme deficiency vs. enzyme trafficking defect)

E77.1 — Defects in glycoprotein degradation: different step in glycoprotein processing

E76.3 — Mucopolysaccharidosis, unspecified: mucolipidoses are NOT mucopolysaccharidoses despite overlapping features

E77.8 — Other disorders of glycoprotein metabolism: for glycoprotein disorders not classified in E77.0 or E77.1

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 E77.0 an HCC code?

Yes. E77.0 maps to Other Significant Endocrine and Metabolic Disorders under the V24 model but is not retained in V28.

Code: E77.0
Description: Defects in post-translational modification of lysosomal enzymes
HCC (V28): No CMS-HCC V28 mapping
RAF: —
Billable: Yes
Payment year: 2026

HCC Category Mapping

V24HCC 23, Other Significant Endocrine and Metabolic Disorders

0.194

ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders

0.036

RxHCCHCC 41, Lysosomal Storage Disorders

3.081

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 E77.0 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for E77.0

For E77.0 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 E77.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

E77.0 is the ICD-10-CM diagnosis code for defects in post-translational modification of lysosomal enzymes. A rare genetic disorder affecting how the body modifies and processes lysosomal enzymes, which are proteins that break down waste materials in cells. E77.0 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, E77.0 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 code requires documentation of the specific enzyme defect when available. Because E77.0 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 E77.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This code requires documentation of the specific enzyme defect when available
•Often associated with lysosomal storage diseases; review clinical findings for more specific diagnosis

Clinical Significance

Defects in post-translational modification of lysosomal enzymes includes mucolipidosis II (I-cell disease) and mucolipidosis III (pseudo-Hurler polydystrophy), where lysosomal enzymes are not properly tagged for delivery to lysosomes. These are severe conditions with clinical features overlapping MPS but with distinct pathophysiology, requiring differentiation for appropriate genetic counseling and management.

Documentation Requirements

✓Specific disorder documented: mucolipidosis II (I-cell disease) or mucolipidosis III (pseudo-Hurler polydystrophy)
✓Confirmatory testing: elevated serum lysosomal enzyme levels, decreased intracellular enzyme activity, or GNPTAB/GNPTG gene mutations
✓Clinical manifestations: skeletal abnormalities, coarse features, developmental delay, cardiac involvement
✓Differentiation from MPS documented (different enzyme trafficking defect mechanism)
✓Treatment plan and current disease status

Commonly Confused Codes

•E76.01: Hurler syndrome: similar clinical features but different pathophysiology (direct enzyme deficiency vs. enzyme trafficking defect)
•E77.1: Defects in glycoprotein degradation: different step in glycoprotein processing
•E76.3: Mucopolysaccharidosis, unspecified: mucolipidoses are NOT mucopolysaccharidoses despite overlapping features
•E77.8: Other disorders of glycoprotein metabolism: for glycoprotein disorders not classified in E77.0 or E77.1