OpiCalc

Favorites Specialties Drugs Guidelines Most Used

All Specialties

Favorites Specialties Drugs Guidelines Most Used

Faves Specs Drugs Guides Top

ACMG/AMP Variant Classifier Amsterdam Criteria II CYP2C19 Phenotype Interpreter DLCN Score (FH)GJB2 Variant Interpreter Ghent-2 Criteria (Marfan)HTT CAG Repeat (Huntington)Hereditary Thrombophilia VTE Risk Revised Bethesda Guidelines Tyrer-Cuzick Breast Risk

OpiCalc

Easy, fast, and private medical tools for clinicians. Always free.

No Login Required

Ready for the Bedside

Resources

About Us Editorial Policy Medical Disclaimer Privacy Policy Terms of Use Cookie Policy

Support

Clinical Notice:OpiCalc is not a substitute for professional clinical judgment. Always verify dosages and guidelines.

OpiCalc © 2018-2026

•

All Rights Reserved

In Recent Clinical News

Scanning Medical Journals

No new significant updates or guidelines matching this topic were found today. We will check again soon.

HTT CAG Repeat (Huntington)

HTT CAG Repeat Interpreter — Huntington Disease

Interprets CAG repeat length from HTT gene analysis. Normal ≤ 26 | Intermediate 27–35 | Reduced penetrance 36–39 | Full penetrance ≥ 40. Presymptomatic testing requires formal genetic counselling protocol.

Enter HTT CAG Repeat Length

CAG repeats

Report from accredited genetic laboratory

Reference Ranges

≤ 26

Normal

27–35

Intermediate

36–39

Reduced Pen.

≥ 40

Full Pen.

Guidelines & Evidence

Verified

Last Review: 2026

When to Use

When to Use

Interpreting CAG repeat length results from HTT (huntingtin) gene diagnostic testing.

Presymptomatic predictive testing in adults at 50% risk (parent with HD).

Clarifying allele status in borderline/intermediate CAG repeat range cases.

Prenatal and preimplantation genetic testing (PGT) in known carriers.

Endorsed by ACMG, ACHDG, and EHN as the definitive molecular diagnostic for Huntington Disease.

Critical Ethical Note

Predictive HD testing must ONLY be performed through a formal presymptomatic testing protocol with pre- and post-test genetic counselling. Testing must never be offered without psychological support infrastructure (ACMG, HDSA guidelines).

Last Comprehensive Review: 2026