**5. Conclusions**

This study has provided further confirmation that CAG repeat length significantly predicts AMO in patients with JOHD. In fact, more than 80% of the variance of AMO was explained by CAG repeat length. This provides additional information that allows for more accurate modeling of JOHD, which is critical for future clinical trials.

**Author Contributions:** Conceptualization, J.L.S., A.D.M., and P.C.N.; methodology, J.L.S. and P.C.N.; software, J.L.S.; validation, A.D.M. and P.C.N.; formal analysis, J.L.S.; investigation, J.L.S. and A.D.M.; resources, P.C.N.; data curation, P.C.N.; writing—original draft preparation, J.L.S.; writing—review and editing, A.D.M. and P.C.N.; visualization, J.L.S.; supervision, P.C.N.; project administration, P.C.N.; funding acquisition, P.C.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by National Institute of Neurological Disorders and Stroke (NINDS; R01NS055903). The APC was funded by National Institute of Neurological Disorders and Stroke (NINDS; R01NS055903).

**Acknowledgments:** Enroll-HD is a longitudinal observational study for Huntington's disease families intended to accelerate progress towards therapeutics; it is sponsored by CHDI Foundation, a nonprofit biomedical research organization exclusively dedicated to developing therapeutics for HD. Enroll-HD would not be possible without the vital contributions of the research participants and their families. We also thank the patients and families that participated in the Predict-HD study and the Kids-JOHD study. We also wish to extend our thanks to the CHDI Foundation for their dedication to advancing scientific discovery in the HD community through data sharing.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
