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The likelihood of being affected with Huntington disease by a particular age, for a specific CAG size
R R Brinkman1, M M Mezei, J Theilmann
1Department of Medical Genetics, University of British Columbia, Vancouver, Canada.
Insights
Huntington disease (HD) CAG repeat size strongly influences age of onset. Larger CAG expansions correlate with earlier symptom onset, aiding in predictive testing and clinical trial design for at-risk individuals.
Area of Science:
- Genetics
- Neurology
- Clinical Research
Background:
- Previous research on Huntington disease (HD) and CAG repeat size focused primarily on affected individuals.
- Understanding the CAG repeat size-age at onset relationship is crucial for genetic counseling and therapeutic development.
Purpose of the Study:
- To analyze the relationship between CAG repeat size and age of onset in a large cohort of both affected and asymptomatic at-risk individuals with Huntington disease (HD).
- To provide data for predictive testing programs and the design of clinical trials for individuals at increased risk for HD.
Main Methods:
- Analysis of a cohort of 1,049 individuals (321 at-risk, 728 affected) with CAG repeat sizes ranging from 29 to 121.
- Kaplan-Meier analysis to generate curves predicting the likelihood of HD onset at specific ages for different CAG repeat lengths (39-50).
- Examination of HD mutation penetrance across various CAG repeat sizes.
Main Results:
- Statistically significant differences (P < .0005) were observed in onset curves based on CAG repeat length, with narrow 95% confidence intervals (+/-10%).
- Complete penetrance of HD was confirmed for CAG sizes of 42 or greater.
- Individuals with CAG repeat lengths between 36-41 showed variable penetrance, with only a proportion developing symptoms within a normal lifespan.
Conclusions:
- CAG repeat size is a significant determinant of age of onset in Huntington disease (HD).
- The study provides valuable data for predicting HD onset likelihood based on specific CAG sizes and age.
- Findings support the utility of this data in predictive genetic testing and the development of targeted clinical trials for HD.
Abstract:
Prior studies describing the relationship between CAG size and the age at onset of Huntington disease (HD) have focused on affected persons. To further define the relationship between CAG repeat size and age at onset of HD, we now have analyzed a large cohort of affected and asymptomatic at-risk persons with CAG expansion. This cohort numbered 1,049 persons, including 321 at-risk and 728 affected individuals with a CAG size of 29-121 repeats. Kaplan-Meier analysis has provided curves for determining the likelihood of onset at a given age, for each CAG repeat length in the 39-50 range. The curves were significantly different (P < .0005), with relatively narrow 95% confidence intervals (95% CI) (+/-10%). Penetrance of the mutation for HD also was examined. Although complete penetrance of HD was observed for CAG sizes of > or = 42, only a proportion of those with a CAG repeat length of 36-41 showed signs or symptoms of HD within a normal life span. These data provide information concerning the likelihood of being affected, by a specific age, with a particular CAG size, and they may be useful in predictive-testing programs and for the design of clinical trials for persons at increased risk for HD.