ICD-10 Code G90.1: Familial dysautonomia (Riley-Day syndrome)

Key Takeaways

ICD-10 Code G90.1 is the billable, specific code for familial dysautonomia (Riley-Day syndrome), valid for FY2026 HIPAA-covered transactions.

G90.1 falls under Chapter 6 (Diseases of the nervous system), block G89-G99, category G90 (Disorders of autonomic nervous system).

G90.0, the parent code for idiopathic peripheral autonomic neuropathy, is non-billable; G90.1 by contrast is specific and billable without additional specificity.

Pabau’s claims management software supports accurate ICD-10 coding workflows, helping practices submit G90.1 and related autonomic disorder codes with complete documentation.

ICD-10 Code G90.1 is the official ICD-10-CM designation for familial dysautonomia, also listed in the tabular with its eponymous name Riley-Day syndrome. The code is billable and specific, meaning it requires no further digit extension and is valid for HIPAA-covered transactions from October 1, 2025 through September 30, 2026 (FY2026), according to the CMS ICD-10-CM update files.

Familial dysautonomia is a hereditary disorder of the autonomic nervous system, classified under Hereditary Sensory and Autonomic Neuropathy Type III (HSAN III). It results from mutations in the ELP1 gene (formerly IKBKAP) and follows an autosomal recessive inheritance pattern. The condition primarily affects individuals of Ashkenazi Jewish descent.

Classification hierarchy for ICD-10 Code G90.1

Understanding where G90.1 sits in the ICD-10-CM structure helps coders apply the correct code quickly and avoid selecting a parent category by mistake.

The WHO’s ICD-10 browser lists G90.1 within the Diseases of the nervous system chapter. The U.S. clinical modification (ICD-10-CM) mirrors this structure but adds specificity for billing and reimbursement purposes under CMS and HIPAA guidelines.

Coders should note that G90.1 sits at the same level as G90.2 (Horner’s syndrome) and G90.3 (Multi-system degeneration of the autonomic nervous system), making accurate history review essential for correct code selection. Cross-referencing the tabular list before assigning the code remains best practice when documentation is ambiguous.

Billable status and valid code information for G90.1

G90.1 is confirmed billable and specific for FY2026. No additional digits are required to achieve specificity, unlike many category-level codes in the ICD-10-CM system.

• Billable: Yes. G90.1 can be submitted as a standalone diagnosis code on HIPAA-covered claims.
• Valid dates: October 1, 2025 through September 30, 2026.
• ICD-10 transition: Reimbursement claims with a date of service on or after October 1, 2015 require ICD-10-CM codes. G90.1 has been active since that transition.
• No exclusions or “Code First” notes: No Excludes 1, Excludes 2, or Code First directives apply specifically to G90.1 in the FY2026 tabular list.
• Inclusion term: The bracketed notation [Riley-Day] is an official inclusion term, not an alternate code. Both “familial dysautonomia” and “Riley-Day syndrome” map directly to G90.1.

Contrast this with G90.0 (Idiopathic peripheral autonomic neuropathy), which is non-billable and requires coders to select G90.01 (Carotid sinus syncope) or G90.09 (Other idiopathic peripheral autonomic neuropathy) for valid claims. Practices coding autonomic disorders frequently encounter this distinction when a patient has mixed or overlapping presentations.

Related codes and G90 category overview

G90.1 sits within a category that covers a wide spectrum of autonomic nervous system disorders. Knowing the neighboring codes helps coders identify the right choice when documentation is ambiguous, and it supports accurate differential coding when a patient carries multiple autonomic diagnoses.

Other nervous-system codes sit in the same chapter and may appear alongside G90.1 when a patient carries overlapping neurological diagnoses, including G59 (mononeuropathy in diseases classified elsewhere) and G14 (postpolio syndrome).

Autonomic neuropathy also appears outside the G90 category. The most common acquired form is diabetic neuropathy, coded as E11.40 (type 2 diabetes with diabetic neuropathy), which coders should distinguish from the hereditary autonomic disorder captured by G90.1.

G90.1 vs G90.9: The key distinction

G90.9 (Disorder of the autonomic nervous system, unspecified) is a common fallback code, but it should not be used when a specific hereditary condition such as familial dysautonomia has been diagnosed. Payers increasingly flag unspecified codes for additional documentation requests, particularly for rare inherited neurological disorders.

When physician notes confirm the Riley-Day diagnosis — through genetic testing or established family history — G90.1 is the appropriate and more defensible choice.

ICD-10 Code G90.1 documentation requirements

Accurate documentation is the difference between a clean claim and a denial. For G90.1, payers expect clinical notes to establish the hereditary basis of the dysautonomia rather than describing it as idiopathic or unspecified. Using digital intake forms that capture family history systematically makes this documentation routine rather than reactive.

• Confirm hereditary or familial basis: Documentation should state familial dysautonomia, Riley-Day syndrome, or HSAN III, not merely “autonomic dysfunction.”
• Genetic or family history evidence: ELP1/IKBKAP gene mutation results or a documented family pedigree strongly support the diagnosis in the medical record.
• Ashkenazi Jewish ancestry notation: While not required for billing, noting ethnic background supports medical necessity when payers review rare hereditary diagnoses.
• Symptom specificity: Record the presenting autonomic symptoms (blood pressure instability, feeding difficulties, sensory deficits) with sufficient clinical detail to justify specialist evaluation and ongoing management.
• Physician authorship: The diagnosing or treating physician must author or co-sign the note. Coder assumptions from lab results alone are insufficient.

The AAPC’s ICD-10-CM code lookup provides additional coding notes and official guideline references that can help documentation teams identify specific requirements for G90 category codes. Practices using practice management software and dedicated clinical documentation software reduce the risk of incomplete records reaching the billing stage.

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MS-DRG grouping and hospital billing for G90.1

For inpatient hospital billing, ICD-10 codes map to Medicare Severity Diagnosis Related Groups (MS-DRGs), which drive reimbursement under the Inpatient Prospective Payment System. G90.1, like most codes in the G90 category, groups under MS-DRG v43.0 assignments for cranial and peripheral nerve disorders.

The neighboring code G90.01 is confirmed to map to MS-DRG 073 (Cranial and peripheral nerve disorders with MCC) and MS-DRG 074 (Cranial and peripheral nerve disorders without MCC).

G90.1 is expected to follow the same grouping logic given its category placement, though coders should verify the specific assignment using the ICD List DRG grouper tool for their facility’s fiscal year grouper version. EHR workflows for rare conditions like G90.1 benefit from purpose-built EHR workflows that flag MS-DRG mapping alerts at coding review.

Sequencing G90.1 in multi-diagnosis encounters

In encounters where familial dysautonomia is the primary reason for the visit, G90.1 should be sequenced as the principal diagnosis. When the visit addresses a complication or manifestation — such as respiratory complications, feeding difficulties, or cardiovascular instability — the complication code takes the principal position, with G90.1 coded as an additional secondary diagnosis.

No “Code First” instructions apply to G90.1 itself. However, coders must review any co-occurring conditions to determine whether combination codes or sequencing guidelines from the ICD-10-CM Official Guidelines for Coding and Reporting apply to the secondary codes in the claim. Using patient record management systems with structured problem lists helps clinical teams track the principal versus secondary distinction encounter by encounter.

Clinical overview of familial dysautonomia for coding context

Coders do not diagnose, but understanding the clinical picture behind G90.1 reduces miscoding and supports medical necessity justification when payers question the diagnosis.

Familial dysautonomia is caused by a splicing mutation in the ELP1 gene (formerly IKBKAP), located on chromosome 9q31. This disrupts the production of the elongator protein complex subunit 1, impairing the development and survival of sensory and autonomic neurons.

The condition is autosomal recessive, meaning a child must inherit one defective copy from each parent to develop the disorder. Carrier frequency in the Ashkenazi Jewish population is approximately 1 in 30, with disease prevalence estimated at around 1 in 3,600 births in that community, according to data cited by the National Organization for Rare Disorders (NORD).

Core clinical features

• Autonomic instability: Blood pressure fluctuations (hypertension with excitement, hypotension with standing), excessive sweating, and blotching of the skin.
• Sensory deficits: Reduced pain and temperature sensitivity, absent corneal reflexes, and diminished deep tendon reflexes.
• Feeding and swallowing difficulties: Dysphagia and aspiration risk are common in infancy and early childhood.
• Respiratory complications: Abnormal ventilatory responses to hypoxia and hypercapnia increase the risk of respiratory crises.
• Absence of overflow tears: Alacrima (inability to produce emotional tears) is a characteristic finding used diagnostically.

When a patient presents with this constellation of features in a child of Ashkenazi Jewish heritage, clinical suspicion should prompt genetic testing. The ELP1 founder mutation accounts for over 99% of cases in this population.

Specialty practices managing these patients benefit from neurology and mental health EMR tools that support longitudinal tracking of complex, multi-system hereditary conditions across encounters.

Coding workflow: How to assign ICD-10 Code G90.1 in practice

A consistent coding workflow eliminates the most common G90.1 errors: landing on the non-billable G90.0, defaulting to the unspecified G90.9, or failing to capture supporting secondary codes. EHR integration for complex diagnoses connects clinical documentation to medical billing workflows, reducing manual lookup errors.

1. Confirm the diagnosis in the physician note: Look for “familial dysautonomia,” “Riley-Day syndrome,” or “HSAN III” explicitly. Vague references to autonomic dysfunction do not support G90.1.
2. Search the ICD-10-CM index: Enter “dysautonomia, familial” in the alphabetic index. The index directs to G90.1 directly. Verify in the tabular list before assigning.
3. Verify billable status: Confirm G90.1 is billable (it is). No additional digits are needed.
4. Review sequencing: Determine whether G90.1 is the principal or an additional diagnosis based on the reason for the encounter.
5. Code concurrent conditions: Identify any complications (respiratory, cardiovascular, nutritional) documented in the same encounter and assign appropriate secondary codes.
6. Submit with supporting documentation: Ensure the claim includes the physician note or relevant sections confirming the hereditary diagnosis.

Pabau’s claims management software supports structured coding review at the point of claim submission, helping billing teams catch sequencing and specificity issues before they reach the payer.

Conclusion

Familial dysautonomia is a rare hereditary condition, but the coding decision for G90.1 is straightforward once the documentation is in place. The code is billable, specific, and valid for FY2026, covering all encounters where a confirmed diagnosis of familial dysautonomia (Riley-Day syndrome) is the reason for or a secondary factor in the visit.

The most common errors – using the non-billable G90.0 parent code or defaulting to the unspecified G90.9 — are preventable with clear physician documentation and a structured coding workflow.

Pabau’s compliance management tools and digital forms help practices build documentation habits that support clean, defensible claims from the outset. To see how Pabau supports complex ICD-10 coding workflows across specialty and rare-disease practices, book a demo.

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