Enroll-HD is a worldwide observational study of individuals who have (or are at-risk for) HD.

Cross-sectional analyses were conducted in North American patients (≥18 years) with manifest HD and Unified Huntington’s Disease Rating Scale (UHDRS) diagnostic confidence level of 4 (“motor abnormalities that are unequivocal signs of HD”). Data included: sociodemographics; UHDRS total functional capacity (TFC) with mapped disease severity (Stages I [TFC score=11-13] to V [TFC score=0]) and maximal chorea scores by body region; and medications.

Among 2205 eligible patients, mean age (±SD) was 53.9±12.9 years, 52.4% were female, with staging as follows: I (n=569), II (n=884), III (n=550), IV (n=156), V (n=42). TMC mean scores increased from 7.9±4.0 (Stage I) to 10.7±6.7 (Stage IV). Based on a maximal chorea score ≥2 (“mild common” or “moderate intermittent” to “marked/prolonged”) in any body region, 70.4% had chorea, which increased from Stage I (61.2%) to IV (77.6%). 647 (29.3%) patients were prescribed medications indicated for chorea any time during Enroll-HD, more commonly in later stages (Stage I=13.4%, II=26.8%, III=42.9%, IV=44.9%, V=61.9%). These chorea medications included tetrabenazine monotherapy (36.0%), tetrabenazine plus an antipsychotic and/or other medication (e.g., amantadine) (10.5%), antipsychotic monotherapy (34.6%), antipsychotic plus other medication (3.9%), and other medication (15.0%). Of 319 patients taking tetrabenazine, 94.4% were taking it for chorea; in contrast, only 36.2% of 793 patients taking an antipsychotic had an indication for chorea.

Interestingly, chorea rates in this study appeared to increase with disease severity, contrary to previous data that demonstrated a lessening of chorea with disease progression. Despite 70.4% of manifest HD patients having chorea, only 29.3% were prescribed medication with an indication for chorea. Results are limited by the inherent constraints of a real-world database.