CurrentConnectiCarePolicy C3894-A

Xenazine (tetrabenazine) Coverage Criteria

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Prior authorization coverage of tetrabenazine/Xenazine for Huntington disease chorea, moderate-to-severe tardive dyskinesia, and Tourette syndrome, subject to condition-specific documentation, prescriber qualifications, dose limits, and contraindication review.

Policy Summary

PayerConnectiCare

PolicyXenazine (tetrabenazine) Coverage Criteria

Policy CodePolicy C3894-A

Change TypeNo material change

Effective DateJun 6, 2026

Next Review DateApr 1, 2027

Key ActionSubmit prior authorization documentation establishing the covered indication, qualified prescriber, applicable age, prescribed dose, and any requirements for doses above 50 mg/day.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

3Covered indication categories

12 monthsInitial authorization

85%Continuation adherence

5 yearsMinimum age: Tourette syndrome

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CurrentConnectiCarePolicy C3894-A

Xenazine (tetrabenazine) Coverage Criteria

Customize your policy alerts

Sign up for ConnectiCare Policy C3894-A alerts

Get alerted when Policy C3894-A changes without checking for updates manually.

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Policy Summary

PayerConnectiCare

PolicyXenazine (tetrabenazine) Coverage Criteria

Policy CodePolicy C3894-A

Change TypeNo material change

Effective DateJun 6, 2026

Next Review DateApr 1, 2027

Key ActionSubmit prior authorization documentation establishing the covered indication, qualified prescriber, applicable age, prescribed dose, and any requirements for doses above 50 mg/day.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

3Covered indication categories

12 monthsInitial authorization

85%Continuation adherence

5 yearsMinimum age: Tourette syndrome

Absolute maximum dose

Coverage Criteria

Initial Therapy: Chorea Associated With Huntington Disease

Coverage for chorea associated with Huntington disease requires ALL of the following:

ALL of the following

ONE of the following
- Huntington disease mutation analysis documents an expanded CAG repeat (≥ 36) in the Huntington gene (HTT), also known as the HD gene.
- Positive family history of Huntington disease with an autosomal dominant inheritance pattern.
Baseline evaluation and documentation of the Total Chorea Score using the Unified Huntington's Disease Rating Scale (UHDRS).
The baseline score is reviewed at continuation of therapy.
The prescriber attests, or the clinical reviewer finds, that the member does not have any FDA-labeled contraindications that have not been addressed in the submitted documentation.

Initial Therapy: Tardive Dyskinesia

Coverage for moderate-to-severe tardive dyskinesia requires ALL of the following:

ALL of the following

Documented diagnosis of moderate-to-severe tardive dyskinesia (TD).
Baseline evaluation documented by an Abnormal Involuntary Movement Scale (AIMS) score or Extrapyramidal Symptom Rating Scale (ESRS) score.
Reauthorization requires a positive response or demonstrated efficacy; the baseline score is reviewed at continuation of therapy.
ONE of the following alternative approaches has had an inadequate response
- Adjustments to possible offending medication(s) known to cause TD, including dose reduction or discontinuation, were attempted but were ineffective in resolving TD symptoms.
- The member was switched from a first-generation to a second-generation antipsychotic.

Initial Therapy: Tourette Syndrome

Coverage for Tourette syndrome requires ALL of the following:

ALL of the following

Documented diagnosis of Tourette syndrome.
Comprehensive Behavioral Intervention for Tics (CBIT) has not been successful or is not accessible for the member.
Documented trial and failure of 3 months of adherent utilization of, or clinical contraindication to, TWO of the following: clonidine, guanfacine, haloperidol, risperidone, aripiprazole, or fluphenazine.
The prescriber attests, or the clinical reviewer finds, that the member does not have any FDA-labeled contraindications that have not been addressed in the submitted documentation.

Continuation Therapy

Continuation of therapy for tardive dyskinesia, chorea associated with Huntington disease, or Tourette syndrome requires ALL of the following:

ALL of the following

Adherence to therapy is at least 85% of the time, as verified by the prescriber or member medication fill history; or adherence is less than 85% because surgery or treatment of an infection caused temporary discontinuation.
- Applicable indication-specific evidence
  - Tardive dyskinesia: Disease stabilization or improvement documented by a decrease from baseline in AIMS score of at least 2 points or ESRS score of at least 4 points.
  - Chorea associated with Huntington disease: Disease stabilization or improvement from baseline in Total Maximal Chorea Scores or chorea symptoms.
  - Tourette syndrome: Disease stabilization or improvement in signs and symptoms of Tourette syndrome.

Indication, Age, and Prescriber Eligibility

The request must meet ALL applicable indication, age, and prescriber requirements:

ALL of the following

Covered indication
- Chorea associated with Huntington disease
  - The member is 18 years of age or older.
  - The drug is prescribed by, or in consultation with, a board-certified neurologist with expertise in Huntington disease.
- Tardive dyskinesia
  - The member is 18 years of age or older.

Doses Above 50 mg/day

For doses greater than 50 mg/day, ALL of the following enhanced requirements apply:

ALL of the following

CYP2D6 genotyping results are submitted and indicate that the member is a CYP2D6 intermediate or extensive metabolizer.
Daily doses above 50 mg should not be administered without CYP2D6 genotyping to determine whether the patient is a poor, intermediate, or extensive metabolizer.
The member has had an adequate trial of 50 mg/day with an inadequate response, supported by documentation of the trial and inadequate response.
The requested dose does not exceed 150 mg/day.≤ 150 mg/day

Coverage requires that FDA-labeled contraindications to Xenazine (tetrabenazine) have been addressed by the prescriber in the submitted documentation. Contraindications include active suicidality; depression that is untreated or undertreated; hepatic impairment; concomitant use of monoamine oxidase inhibitors (including selegiline, isocarboxazid, phenelzine, or tranylcypromine), reserpine, deutetrabenazine, or valbenazine; congenital long QT syndrome; and a history of cardiac arrhythmias.

Requests for doses greater than the maximum recommended dose of 150 mg daily will not be authorized for any member.

Xenazine must not be used concurrently with other VMAT2 inhibitors, including valbenazine or deutetrabenazine. Concomitant use with contraindicated medications, including MAOIs or reserpine, is also not covered unless the applicable contraindication has been addressed as required by the policy.

All other uses of Xenazine (tetrabenazine) outside chorea associated with Huntington disease, tardive dyskinesia, or Tourette syndrome are considered experimental/investigational and are subject to the applicable off-label policy.

Initial Therapy Criteria

Huntington Disease Chorea

Initial therapy requires qualifying Huntington disease chorea documentation, baseline assessment, and contraindication review.

Huntington disease chorea

Disease confirmation
- Genetic confirmation: HTT mutation analysis shows an expanded CAG repeat of at least 36.
- Family-history confirmation: There is a positive family history of Huntington disease with autosomal dominant inheritance.
Baseline assessment: Baseline evaluation and Total Chorea Score using the Unified Huntington's Disease Rating Scale are documented.

Continuation and Reauthorization

Tetrabenazine Continuation

Continuation requires ALL of the following.

Continuation requirements

Adherence is at least 85% based on prescriber verification or medication fill history, or adherence below 85% is due to surgery or infection treatment causing temporary discontinuation.
Clinical response: The condition has stabilized or improved based on the prescriber's assessment.
Safety: There is no evidence of intolerable adverse effects or drug toxicity.

Reauthorization

Reauthorization must continue to meet the applicable indication, prescriber, dose, and documentation requirements.

Clinical Thresholds and Documentation Values

Huntington Disease Genetic Confirmation

Genetic confirmationHTT mutation analysis showing an expanded CAG repeat of at least 36 in the Huntington gene.

Alternative confirmationA positive family history of Huntington disease with autosomal dominant inheritance may also qualify.

Baseline documentationDocument a baseline evaluation and Total Chorea Score using the Unified Huntington's Disease Rating Scale (UHDRS).

Continuation Adherence

Minimum adherenceAt least 85% of the time.

VerificationAdherence is verified by the prescriber or the member's medication fill history.

Authorization and Documentation Requirements

Prior Authorization

Prior Authorization and Authorization Duration

Prior authorization is required for initial and continuation requests for Xenazine (tetrabenazine). Authorization is issued for 12 months initially and for 12 months at continuation, subject to applicable coverage criteria.

Submit the required medical information and supporting documentation with each request.
Coverage may be reviewed case by case when updated FDA labeling, member-specific dosing data, or additional information is relevant.

Prior Authorization

Coverage Criteria and Authorization Requirements

Coverage requires a qualifying indication and satisfaction of the applicable prescriber, age, dose, and documentation requirements. Submit clinical records supporting the diagnosis, treatment plan, requested dose, and all applicable prerequisites.

Huntington disease chorea: documentation of an expanded HTT CAG repeat of at least 36 or a positive autosomal-dominant family history, plus baseline UHDRS Total Chorea Score.
Tardive dyskinesia: documented moderate-to-severe TD, baseline AIMS or ESRS score, and inadequate response or clinical ineligibility for at least one alternative approach.

Required Alternative Therapy Trials

Step	Requirement	Duration / outcome
1	Tourette syndrome: trial and failure of, or clinical contraindication to, TWO of the following medications: clonidine, guanfacine, haloperidol, risperidone, aripiprazole, or fluphenazine.	3 months of adherent utilization, with failure, or clinical contraindication

Step	Requirement	Acceptable alternative approach / outcome
1	Tardive dyskinesia: document an inadequate response to at least ONE alternative approach.	Dose reduction or discontinuation of the offending medication was attempted but ineffective; switch from a first-generation to a second-generation antipsychotic; switch to an antipsychotic with a different mechanism of action; or documentation that the member is not a candidate for these changes.

Dosage and Quantity Limits

Xenazine (Tetrabenazine) Dose Limits

Standard maximum dose50 mg per day.

High-dose authorizationDoses above 50 mg/day require CYP2D6 genotyping showing an intermediate or extensive metabolizer and documentation of an adequate 50 mg/day trial with inadequate response.

Maximum authorized dose150 mg daily; requests above 150 mg/day will not be authorized.

Benefit and Administration Setting

Billing Rule

Bill oral Xenazine under the pharmacy benefit

Oral medication under this policy is covered through the pharmacy benefit and is intended for patient self-administration.

Route of administration: oral.
Site of care: patient self-administration.

Policy Background

This policy addresses prior authorization for oral tetrabenazine (Xenazine) used to treat chorea associated with Huntington disease, moderate-to-severe tardive dyskinesia, and Tourette syndrome. Coverage requires indication-specific clinical documentation, appropriate prescriber qualifications, and review of contraindications; continuation also depends on adherence and documented clinical stabilization or improvement.

Definitions and Abbreviations

Expanded CAG Repeat

TestHTT mutation analysis.

FindingAn expanded CAG repeat of at least 36.

GeneThe Huntington gene, also known as HTT or the HD gene.

AIMS

AbbreviationAIMS.

Full nameAbnormal Involuntary Movement Scale.

Policy useUsed to document the baseline evaluation and assess response during reauthorization.

Policy Summary

PayerConnectiCare

PolicyXenazine (tetrabenazine) Coverage Criteria

Policy CodePolicy C3894-A

Change TypeNo material change

Effective DateJun 6, 2026

Next Review DateApr 1, 2027

Key ActionSubmit prior authorization documentation establishing the covered indication, qualified prescriber, applicable age, prescribed dose, and any requirements for doses above 50 mg/day.

SourceLink

On This Page

The member was switched to an antipsychotic with a different mechanism of action, such as xanomeline/trospium.

The member is not a candidate for a trial of dose reduction, tapering, discontinuation of the offending medication, or switching to an alternative antipsychotic therapy.

The prescriber attests, or the clinical reviewer finds, that the member does not have any FDA-labeled contraindications that have not been addressed in the submitted documentation.

The prescriber attests, or the clinical reviewer finds, that there is no evidence of intolerable adverse effects or drug toxicity.

The drug is prescribed by, or in consultation with, a board-certified psychiatrist or neurologist.

Tourette syndrome

The member is 5 years of age or older.
The drug is prescribed by, or in consultation with, a board-certified psychiatrist or neurologist.

If prescribed in consultation, consultation notes must be submitted with the initial request and reauthorization requests.

Contraindication review: The prescriber attests, or the clinical reviewer finds, that the member has no unaddressed FDA-labeled contraindication to Xenazine.

Tardive Dyskinesia

Initial therapy requires ALL applicable tardive dyskinesia criteria.

Tardive dyskinesia

Diagnosis: Documented diagnosis of moderate-to-severe tardive dyskinesia.Moderate to severe
Baseline assessment: Baseline evaluation is documented by AIMS score or ESRS score.
Alternative treatment response
- Medication adjustment: Dose reduction or discontinuation of a possible offending medication was attempted but ineffective in resolving symptoms.
- Antipsychotic switch: The member was switched from a first-generation to a second-generation antipsychotic.
- Different mechanism switch: The member was switched to an antipsychotic with a different mechanism of action.
- Clinical ineligibility: The member is not a candidate for dose reduction, tapering, discontinuation, or switching to an alternative antipsychotic therapy.
Contraindication review: The prescriber attests, or the clinical reviewer finds, that the member has no unaddressed FDA-labeled contraindication to Xenazine.

Tourette Syndrome

Initial therapy requires ALL applicable Tourette syndrome criteria.

Tourette syndrome

Diagnosis: Documented diagnosis of Tourette syndrome.
CBIT prerequisite: CBIT was unsuccessful or is not accessible for the member.
Medication trials: There was a trial and failure of 3 months of adherent utilization of, or a clinical contraindication to, two of clonidine, guanfacine, haloperidol, risperidone, aripiprazole, or fluphenazine.2 medications; 3 months
Contraindication review: The prescriber attests, or the clinical reviewer finds, that the member has no unaddressed FDA-labeled contraindication to Xenazine.

Initial Therapy Eligibility

Initial coverage requires the applicable indication, prescriber qualification, age requirement, and dose criteria.

Initial authorization eligibility: The requested use is a covered indication; the member meets the indication-specific minimum age; the prescriber meets the required specialty qualification; and the prescribed dose is within the applicable limit or satisfies the high-dose exception requirements.Tourette syndrome: age ≥ 5 years; Huntington disease chorea or tardive dyskinesia: age ≥ 18 years; absolute maximum dose: 150 mg/day

Submit consultation notes when the prescription is issued in consultation. Doses above 50 mg/day require CYP2D6 genotyping and documentation of inadequate response to 50 mg/day.

Reauthorization requirements

Covered indication and prescriber: The member continues to meet the covered indication and applicable prescriber qualification requirements.
Dose requirements: The requested dose does not exceed 150 mg/day and any dose greater than 50 mg/day is supported by the required CYP2D6 genotype and inadequate-response documentation.Maximum: 150 mg/day
Documentation: Required consultation notes are submitted when the drug is prescribed in consultation.

Allowed interruption

Adherence below 85% may qualify when surgery or infection treatment caused a temporary discontinuation.

Tardive Dyskinesia AIMS Response

MeasureAbnormal Involuntary Movement Scale (AIMS).

Required responseDecrease from baseline of at least 2 points.

Continuation assessmentThe decrease documents stabilization or improvement in tardive dyskinesia symptoms.

Tardive Dyskinesia ESRS Response

MeasureExtrapyramidal Symptom Rating Scale (ESRS).

Required responseDecrease from baseline of at least 4 points.

Continuation assessmentThe decrease documents stabilization or improvement in tardive dyskinesia symptoms.

Tourette Alternative Therapy Trial

Required duration3 months.

Utilization standardThe trial must involve adherent utilization.

OutcomeThe two selected therapies must have failed, unless there is a clinical contraindication.

Tourette syndrome: documented diagnosis, unsuccessful or inaccessible CBIT, and trial and failure of 3 months of adherent use of—or clinical contraindication to—two specified medications.

Meet specialty prescriber and minimum age requirements.

Maximum and high-dose requirements must be met, including CYP2D6 documentation when applicable.

Step Therapy

Tardive Dyskinesia Alternatives

For tardive dyskinesia, document an inadequate response to at least one alternative approach before requesting Xenazine.

Attempted dose reduction or discontinuation of the offending medication without adequate resolution of TD symptoms.
Switch from a first-generation to a second-generation antipsychotic.
Switch to an antipsychotic with a different mechanism of action, such as xanomeline/trospium.
Documentation that the member is not a candidate for dose reduction, tapering, discontinuation, or switching to an alternative antipsychotic.

Step Therapy

Tourette Syndrome Prerequisites

For Tourette syndrome, document that Comprehensive Behavioral Intervention for Tics (CBIT) was unsuccessful or inaccessible and that required medication prerequisites have been met.

Document a trial and failure of 3 months of adherent use of, or a clinical contraindication to, two of the following: clonidine, guanfacine, haloperidol, risperidone, aripiprazole, or fluphenazine.

Documentation Required

General Medical Necessity Documentation

The plan may require additional documentation to support medical necessity, non-investigational status, benefit coverage, and appropriate utilization. Incomplete or unsupported documentation may result in denial or other appropriate action.

Patient medical records and relevant test results.
Credentials of the provider ordering or performing the service.
Member-specific dosing data when dosing is based on weight, body surface area, or another individual measurement.
Any additional information needed for adequate review.

Documentation Required

Huntington Disease Documentation

For Huntington disease chorea, submit documentation supporting the diagnosis and genetic or clinical basis for Huntington disease.

HTT mutation analysis showing an expanded CAG repeat of at least 36; or
Positive family history consistent with autosomal-dominant inheritance.
Baseline evaluation and UHDRS Total Chorea Score are also required.

Documentation Required

Tardive Dyskinesia Documentation

For tardive dyskinesia, document moderate-to-severe disease, a baseline severity assessment, and the member’s response to prior treatment approaches.

Baseline AIMS or ESRS score is required.
Document inadequate response to at least one qualifying alternative approach or that the member is not a candidate for those alternatives.
The baseline score is reviewed at continuation; reauthorization requires positive response or demonstrated efficacy.

Documentation Required

Tourette Syndrome Documentation

For Tourette syndrome, submit documentation establishing the diagnosis and showing completion or inaccessibility of CBIT and the required medication trials.

Documented Tourette syndrome diagnosis.
CBIT was unsuccessful or is not accessible.
Trial and failure of 3 months of adherent use of, or clinical contraindication to, two specified medications.

Documentation Required

Continuation Documentation

Continuation requests must document ongoing appropriate use and clinical benefit. Reauthorization requires adherence, stabilization or improvement, and absence of intolerable adverse effects or toxicity.

Adherence of at least 85% based on prescriber verification or medication fill history, unless a temporary interruption was required for surgery or infection treatment.
TD: at least a 2-point decrease from baseline in AIMS score or a 4-point decrease in ESRS score.
Huntington disease chorea: stabilization or improvement in Total Maximal Chorea Scores or chorea symptoms.
Tourette syndrome: stabilization or improvement in signs and symptoms.

Documentation Required

Consultation Documentation

When Xenazine is prescribed in consultation, submit the consultation documentation with both the initial authorization request and each reauthorization request.

Consultation notes must support the indication, treatment plan, and requested dose.

Documentation Required

Consultation Notes Required

If the drug is prescribed in consultation, the required consultation notes must accompany the request rather than being submitted only upon request.

Initial requests: submit consultation notes.
Reauthorization requests: submit updated consultation notes.

Documentation Required

High-Dose Documentation

Requests for doses above 50 mg per day require documentation that the member is an appropriate CYP2D6 metabolizer and that 50 mg per day was tried without adequate response.

Submit CYP2D6 genotyping results showing intermediate or extensive metabolizer status.
Document an adequate trial of 50 mg per day and inadequate response.
Doses above 50 mg per day may not exceed 150 mg daily; doses above 150 mg daily will not be authorized.

Denial Risk

Unaddressed Contraindications

Coverage may be denied when an FDA-labeled contraindication is present or when the prescriber does not address the contraindication in the submitted documentation.

Actively suicidal or untreated or inadequately treated depression.
Hepatic impairment.
Concurrent MAOI, reserpine, deutetrabenazine, or valbenazine use.
Congenital long QT syndrome or a history of cardiac arrhythmias.

Denial Risk

Insufficient Tardive Dyskinesia Documentation

A tardive dyskinesia request may be denied when disease severity, a baseline movement-disorder scale, or the required response to prior treatment is not documented.

Document moderate-to-severe TD.
Provide a baseline AIMS or ESRS score.
Document inadequate response to a qualifying alternative approach or why alternatives are clinically inappropriate.
Continuation requests must include positive response or demonstrated efficacy.

Denial Risk

Unmet Tourette Treatment Prerequisites

A Tourette syndrome request may be denied when CBIT requirements or the required medication prerequisites are not documented.

Document that CBIT was unsuccessful or inaccessible.
Document 3 months of adherent use and failure of, or a clinical contraindication to, two specified medications.

Denial Risk

Failure of Continuation Criteria

Continuation authorization may be denied when adherence, clinical benefit, or other continuation requirements are not demonstrated.

Adherence below 85% without an allowed temporary interruption.
No documented stabilization or improvement from baseline.
Intolerable adverse effects or drug toxicity.
Missing required continuation assessments or supporting documentation.

Denial Risk

Prescriber Requirements Not Met

Requests may be denied when the prescriber does not meet the specialty qualification required for the indication.

TD and Tourette syndrome: prescribing or consultation by a board-certified psychiatrist or neurologist.
Huntington disease chorea: prescribing or consultation by a board-certified neurologist with expertise in Huntington disease.
Submit consultation notes when the drug is prescribed in consultation.

Denial Risk

Age Requirements Not Met

Requests may be denied when the member does not meet the minimum age requirement for the requested indication.

Tourette syndrome: member must be at least 5 years old.
Huntington disease chorea and tardive dyskinesia: member must be at least 18 years old.

Denial Risk

Dose Limits and High-Dose Rules

Requests may be denied when the requested dose exceeds policy limits or when required high-dose documentation is missing.

Doses above 50 mg per day require CYP2D6 genotyping and documentation of an inadequate response to an adequate 50 mg per day trial.
Maximum authorized dose is 150 mg daily.
Requests above 150 mg daily will not be authorized.

Denial Risk

Prescriber or Age Criteria Not Met

Failure to meet the applicable specialty prescriber or minimum age criteria is a denial condition, even when the indication is otherwise supported.

Verify the prescriber or consultant’s board certification and indication-specific expertise.
Verify age: at least 5 years for Tourette syndrome and at least 18 years for Huntington disease chorea or tardive dyskinesia.

Denial Risk

Other Uses Are Experimental or Investigational

Uses of Xenazine other than covered Huntington disease chorea, tardive dyskinesia, or Tourette syndrome criteria are considered experimental or investigational and are handled under the plan’s Off-Label policy.

Submit supporting evidence and documentation required by the applicable Off-Label policy for other uses.

Denial Risk

Contraindications and Concurrent VMAT2 Therapy

Do not authorize or continue Xenazine when applicable psychiatric contraindications, interacting medications, or concurrent VMAT2 therapy are present and not appropriately addressed.

Contraindications include active suicidality, untreated or undertreated depression, and hepatic impairment.
Do not use with MAOIs, reserpine, deutetrabenazine, or valbenazine.
Do not use concurrently with another VMAT2 inhibitor, including valbenazine or deutetrabenazine.
Assess for depression, suicidality, and unusual behavioral changes during treatment.

Denial Risk

Cardiac Risk Exclusions

Xenazine should be avoided in members with congenital long QT syndrome or a history of cardiac arrhythmias. Requests with these cardiac risks may be excluded or denied.

Document that congenital long QT syndrome is absent.
Document that there is no history of cardiac arrhythmias or explain how the risk has been addressed.

ESRS

AbbreviationESRS.

Full nameExtrapyramidal Symptom Rating Scale.

Policy useUsed to document the baseline evaluation and assess response during reauthorization.

CBIT

AbbreviationCBIT.

Full nameComprehensive Behavioral Intervention for Tics.

Tourette prerequisiteCBIT must be unsuccessful or inaccessible for the member.

VMAT2 Inhibitor

AbbreviationVMAT2 inhibitor.

Full nameVesicular Monoamine Transporter 2 inhibitor.

Therapeutic roleVMAT2 inhibitors are included among pharmacologic treatments for chorea associated with Huntington disease.

Tardive Dyskinesia

Clinical conditionA potentially irreversible involuntary movement disorder.

Movement patternCharacterized by repetitive choreiform or athetoid movements.

Common distributionOften involves the orofacial region, trunk, and extremities.

Huntington Disease–Associated Chorea

Disorder typeA hyperkinetic movement disorder.

Movement patternInvoluntary, irregular, and unpredictable muscle movements.

Primary areas affectedPrimarily affects the face, trunk, and limbs.

Huntington Disease Chorea

Disease typeA progressive neurodegenerative condition.

Genetic causeCaused by a CAG trinucleotide repeat expansion in the HTT gene.

Characteristic manifestationChorea involving the face, trunk, and limbs.