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The HD-ISS Calculator is a CHDI Foundation collaborative project. CHDI is committed to open science, but any modifications to the HD-ISS Calculator or its underlying code may alter validity of the output. The HD-ISS Calculator and its underlying code are being made available pursuant to a Creative Commons Attribution-NoDerivatives 4.0 International Public License. If you would like to create a derivative work of the HD-ISS Calculator or its underlying code, or have other questions, please contact info@chdifoundation.org to discuss.

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HD-ISS Calculator

Based on the paper, A biological classification of Huntington's disease: the Integrated Staging System, by Tabrizi et al.

Directions: insert values for each variable indicated (missing data is not allowed). Then click Calculate Stage for results.


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Age in Years

Round to nearest year (18 or older)

 CAG Expansion

Must be 40 or longer

Putamen Volume

Must be proportion of
ICV ICV: intra-cranial volume
(range 0 to 1)

Caudate Volume

Must be proportion of
ICV ICV: intra-cranial volume
(range 0 to 1)

UHDRS UHDRS: Unified HD Rating Scale
Total Motor Score (TMS)

Range 0 to 124
UHDRS UHDRS: Unified HD Rating Scale
Symbol Digit Modalities Test (SDMT)
(0 or greater)

Education: Required for SDMT interpretation
0 = HS or less, 1 = more than HS
(0 or 1)
UHDRS UHDRS: Unified HD Rating Scale
Total Functional Capacity (TFC)

Range 0 to 13
UHDRS UHDRS: Unified HD Rating Scale
Independence Scale (IS)

Range 0 to 100 (increments of 10)

Huntington's Disease Integrated Staging System Overview

stage