What is ICD-10 code E76.1?

E76.1 is the ICD-10-CM diagnosis code for Mucopolysaccharidosis, type II. Mucopolysaccharidosis type II, also known as Hunter syndrome, is an inherited disorder where the body accumulates complex sugars in cells, causing progressive damage to organs, bones, and the nervous system. E76.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. E76.1 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. E76.1 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. E76.1 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 E76.1?

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. For E76.1, V28 maps to Lysosomal Storage Disorders at RAF 0.226 while V24 mapped to Other Significant Endocrine and Metabolic Disorders at RAF 0.230. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting E76.1?

MPS II is X-linked recessive; document whether the patient is a carrier, affected male, or affected female Specify the severity (mild, moderate, or severe) if documented, as this affects management and prognosis Because E76.1 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.

E76.1 ICD-10 Code: Mucopolysaccharidosis, type II

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupE76.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

E76.1

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

Mucopolysaccharidosis, type II

Mucopolysaccharidosis type II, also known as Hunter syndrome, is an inherited disorder where the body accumulates complex sugars in cells, causing progressive damage to organs, bones, and the nervous system.

Buddy Insight

CMS-HCC V28

Mapped

HCC 49

Lysosomal Storage Disorders

RAF 0.226

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 41

Lysosomal Storage Disorders

RAF 0.0

Code Trumping

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Code Book Path

Official

E76Disorders of glycosaminoglycan metabolism

E76.1Mucopolysaccharidosis, type II

Inclusion Terms

Official

Hunter's syndrome

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for E76.1 in this effective period.

Related Child Codes

Official

E76.0Mucopolysaccharidosis, type I

E76.2Other mucopolysaccharidoses

E76.3Mucopolysaccharidosis, unspecified

E76.8Other disorders of glucosaminoglycan metabolism

E76.9Glucosaminoglycan metabolism disorder, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for E76.1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for E76.1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for E76.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for E76.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for E76.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Specific diagnosis of MPS II (Hunter syndrome) documented by provider

Confirmatory enzyme assay showing iduronate-2-sulfatase deficiency or IDS gene mutation analysis

Disease severity classification (severe/neuronopathic vs. attenuated/non-neuronopathic)

Current manifestations: coarse facial features, hepatosplenomegaly, cardiac involvement, skeletal abnormalities, airway obstruction

MEAT Support

HCC Buddy guidance

Specific diagnosis of MPS II (Hunter syndrome) documented by provider

Confirmatory enzyme assay showing iduronate-2-sulfatase deficiency or IDS gene mutation analysis

Disease severity classification (severe/neuronopathic vs. attenuated/non-neuronopathic)

Current manifestations: coarse facial features, hepatosplenomegaly, cardiac involvement, skeletal abnormalities, airway obstruction

Audit Caution

HCC Buddy guidance

Confusing Hunter (MPS II, X-linked) with Hurler (MPS I, autosomal recessive) — Hunter lacks corneal clouding

Failing to identify the X-linked inheritance pattern which helps distinguish MPS II from other MPS types

Using E76.3 (unspecified MPS) when Hunter syndrome is documented

Not coding the associated cardiac, respiratory, and skeletal manifestations as additional diagnoses

Common Mistakes

HCC Buddy guidance

E76.01 — Hurler syndrome (MPS I-H): autosomal recessive, different enzyme (alpha-L-iduronidase), includes corneal clouding (absent in Hunter)

E76.22 — Sanfilippo syndrome (MPS III): primarily neurological with behavioral changes, different enzyme deficiencies

E76.210 — Morquio A (MPS IVA): predominantly skeletal with normal intelligence

E76.29 — Other mucopolysaccharidoses: for MPS types without specific codes (VI, VII, IX)

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 E76.1 an HCC code?

Yes. E76.1 maps to Lysosomal Storage Disorders under the CMS-HCC V28 risk adjustment model (and Other Significant Endocrine and Metabolic Disorders under V24).

HCC Category Mapping

V28HCC 49, Lysosomal Storage Disorders

0.226

V24HCC 23, Other Significant Endocrine and Metabolic Disorders

0.230

ESRDHCC 23, Other Significant Endocrine and Metabolic Disorders

0.000

RxHCCHCC 41, Lysosomal Storage 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.

MEAT Criteria for E76.1

For E76.1to 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 E76.1 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

E76.1 is the ICD-10-CM diagnosis code for mucopolysaccharidosis, type ii. Mucopolysaccharidosis type II, also known as Hunter syndrome, is an inherited disorder where the body accumulates complex sugars in cells, causing progressive damage to organs, bones, and the nervous system. E76.1 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, E76.1 maps to Lysosomal Storage Disorders (HCC 49) with a community, non-dual, aged base RAF weight of 0.226. Under the older CMS-HCC V24 model, E76.1 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.

MPS II is X-linked recessive; document whether the patient is a carrier, affected male, or affected female. Because E76.1 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 E76.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•MPS II is X-linked recessive; document whether the patient is a carrier, affected male, or affected female
•Specify the severity (mild, moderate, or severe) if documented, as this affects management and prognosis

Clinical Significance

Mucopolysaccharidosis type II (Hunter syndrome) is an X-linked recessive lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase, leading to accumulation of dermatan and heparan sulfate. It primarily affects males and ranges from severe (with neurodegeneration) to attenuated forms, requiring enzyme replacement therapy and multidisciplinary care.

Documentation Requirements

✓Specific diagnosis of MPS II (Hunter syndrome) documented by provider
✓Confirmatory enzyme assay showing iduronate-2-sulfatase deficiency or IDS gene mutation analysis
✓Disease severity classification (severe/neuronopathic vs. attenuated/non-neuronopathic)
✓Current manifestations: coarse facial features, hepatosplenomegaly, cardiac involvement, skeletal abnormalities, airway obstruction
✓Treatment status: enzyme replacement therapy (idursulfase/Elaprase), intrathecal therapy, or supportive care

Commonly Confused Codes

•E76.01 — Hurler syndrome (MPS I-H): autosomal recessive, different enzyme (alpha-L-iduronidase), includes corneal clouding (absent in Hunter)
•E76.22 — Sanfilippo syndrome (MPS III): primarily neurological with behavioral changes, different enzyme deficiencies
•E76.210 — Morquio A (MPS IVA): predominantly skeletal with normal intelligence
•E76.29 — Other mucopolysaccharidoses: for MPS types without specific codes (VI, VII, IX)