There is growing consensus that intervention and treatment of Huntington disease (HD) should occur at the earliest stage possible. Various early-intervention methods for this fatal neurodegenerative disease have been identified, but preventive clinical trials for HD are limited by a lack of knowledge of the natural history of the disease and a dearth of appropriate outcome measures. Objectives of the current study are to document the natural history of premanifest HD progression in the largest cohort ever studied and to develop a battery of imaging and clinical markers of premanifest HD progression that can be used as outcome measures in preventive clinical trials. Neurobiological predictors of Huntington’s disease is a 32-site, international, observational study of premanifest HD, with annual examination of 1013 participants with premanifest HD and 301 gene-expansion negative controls between 2001 and 2012. Findings document 39 variables representing imaging, motor, cognitive, functional, and psychiatric domains, showing different rates of decline between premanifest HD and controls. Required sample size and models of premanifest HD are presented to inform future design of clinical and preclinical research. Preventive clinical trials in premanifest HD with participants who have a medium or high probability of motor onset are calculated to be as resource-effective as those conducted in diagnosed HD and could interrupt disease 7–12 years earlier. Methods and measures for preventive clinical trials in premanifest HD more than a dozen years from motor onset are also feasible. These findings represent the most thorough documentation of a clinical battery for experimental therapeutics in stages of premanifest HD, the time period for which effective intervention may provide the most positive possible outcome for patients and their families affected by this devastating disease.

BACKGROUND Although correlation between cytosine-adenine-guanine (CAG) repeat length and age of Huntington disease (HD) onset is well known, improved prediction of onset would be advantageous for clinical trial design and prognostic counseling. We compared genetic, demographic, motor, cognitive, psychiatric, functional and imaging measures for tracking progression and predicting conversion to manifest HD. METHODS N=1078 research participants with the gene mutation for HD, but without a rating of 4 on the Diagnostic Confidence Level (DCL) following administration of the 15-item motor assessment of the Unified Huntington’s Disease Rating Scale. Participants were from 33 world wide sites and followed for up to 12 years (mean=5, SD=3·3) over the period 2001–2013. A subset of 225 participants prospectively converted to manifest HD according to the DCL (“meets the operational definition of the unequivocal presence of an otherwise unexplained extrapyramidal movement disorder in a subject at risk for HD” with ≥99% confidence). Joint modeling of longitudinal and survival data was used to examine the extent to which baseline and change of 40 variables analyzed separately was predictive of CAG-adjusted age at motor diagnosis. FINDINGS Cross-sectional and longitudinal clinical and imaging measures were significant predictors of motor diagnosis beyond CAG repeat length and age. The strongest predictors in the top three phenotypic domains were total motor score (motor), putamen volume (imaging), and Stroop word test (cognitive). A one standard deviation (SD) difference in total motor score increased the risk of a motor diagnosis by 3·1 times (95% CI=[2·3,4·2]), one SD loss in putamen volume increased risk by 3·3 times ([2·4,4·7]) and one SD cognitive decline increased risk by 2·3 ([1·9,2·9]). INTERPRETATION Prediction of HD diagnosis can be considerably improved beyond that obtained by CAG repeat length and age alone. Such knowledge about potential predictors of manifest HD should inform discussions about revisions to guidelines for diagnosis, and prognosis, and counselling, and might be useful in guiding selection of participants and outcome measures for clinical trials. FUNDING National Institutes of Health, National Institute of Neurological Disorders and Stroke, and CHDI Foundation, Inc.

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