Huntington’s disease (HD) is a neurodegenerative movement disorder caused by abnormal cytosine-adenine-guanine (CAG) expansion on the HTT gene. As both a proteinopathy and the most common PolyQ disease, HD shares key features with several disorders that disproportionately affect the growing elderly population in the United States, including delayed-onset, selective neuronal death, and protein misfolding. Across these conditions, there are few treatments and no known cures; however, their shared features suggest common underlying mechanisms, and delayed-onset hints at possible prevention or reversal. CAG-expansion-number and age are related to diagnosis and can be used to estimate age-of-onset for prodromal (pre-diagnosis) individuals, who possess the causal mutation but have not manifested diagnosis-associated motor symptoms. Over a decade before diagnosis, prodromal individuals differ from controls in brain structure and connectivity, cognition, and motor functioning. Although age and CAG-number account for most observed variability in HD-onset, persons with identical CAG-numbers often develop symptoms at different ages, indicating that additional genetic and environmental factors also mediate decline. Little is known about detrimental and protective genetic factors in HD. Studying prodromal progression can inform interventions by highlighting early prevention targets.

This research leverages advanced multivariate techniques applied to legacy PREDICT-HD data to characterize brain structure, cognition, and motor functioning across prodromal HD and investigate genetic factors accounting for variability in these domains. Regarding brain structure, these experiments provide evidence for: regional co-occurrence in prodromal decline, early fronto-striatal degradation, dorso-ventral reduction gradients, and delayed atrophy in certain movement-related and subcortical regions. The genetic findings suggest a protective role of NTRK2 and identify NCOR1 and ADORA2B variants with early, CAG-independent detrimental effects on gray matter. Previously identified onset-delaying variants are also confirmed as CAG-independent modulators of brain structure and clinical functioning. Clinical findings highlight motor functioning as the best indicator of brain-structural integrity until the late prodrome and demonstrate that distinct regions coincide with cognitive compared to motor functioning; furthermore, regions that most align with clinical functioning vary at different prodromal stages.