[346/ 350 words]Background and Objectives:Huntington’s Disease (HD) is a rare, inherited and highly complex neuro-degenerative disorder with no currently approved disease modifying treatments. We investigated the impact of HD on health-related quality of life (HRQoL) and other patient-reported outcomes in the Huntington’s Disease Burden of Illness (HDBOI) study.Methods:The HDBOI study is a retrospective, cross-sectional study conducted between September 2020 and May 2021 in France, Germany, Italy, Spain, the United Kingdom and the United States. People with symptomatic onset HD (PwHD) were recruited by their HD-treating physicians and categorized as early (ES), mid (MS) or advanced stage (AS) HD. Physicians provided sociodemographic and clinical information from the participant’s medical records in electronic case report forms (eCRF); participants or their proxies completed online Patient Public Involvement Engagement questionnaires (PPIE-P). Patient-reported outcomes included the EQ-5D-5L, SF-36 v2 (and SF-6D utility), Huntington Quality of Life Instrument (H-QoL-I), and the Work Productivity and Activity Impairment Specific Health Problem (WPAI-SHP). All outcomes were summarized using descriptive statistics, differences between disease stages were assessed by Kruskal-Wallis tests.Results:A total of 2,094 PwHD were enrolled with completed eCRFs (100%) and PPIE-P forms (n=482, 23%). Participants mean age was 47.3 years, they were generally evenly distributed across countries, with the majority being ES (40%) followed by MS (33%) and LS (26%). Mean EQ-5D-5L (n=336) utility scores was 0.59 (SD, 0.27), with the highest mean utility scores [SD] in ES (0.72 [0.22]) followed by MS (0.62 [0.18]) and AS (0.37 [0.30]), p<0.001. Mean SF-6D score (n=482) was 0.57 (SD, 0.10), with mean values decreasing with advanced disease (ES, 0.61; MS, 0.56; AS, 0.50, p<0.001). H-QoL-I mean scores (n=482) also worsened with more advanced disease, from 0.58 for ES to 0.49 for MS and 0.37 for AS, p<0.001. Impairment in daily activities and in work productivity. Overall proxy-respondents reported on average worse outcomes than PwHD (self-reported) across all outcomes and disease stages suggesting a possible unawareness of deficits by PwHD.Conclusion:The HDBOI study provides new insights into the characteristics and humanistic burden of PwHD, and offers a meaningful contribution to this underserved research area.

Background and purpose:The prevalence of Huntington disease (HD) has increased over time; however, there is a lack of up-to-date evidence documenting the economic burden of HD by disease stage. This study provides an estimate of the annual direct medical, nonmedical, and indirect costs associated with HD from participants in the Huntington's Disease Burden of Illness (HDBOI) study in five European countries and the USA. Methods:The HDBOI is a retrospective, cross-sectional study. Data collection was conducted between September 2020 and May 2021. Participants were recruited by their HD-treating physicians and categorized as early stage (ES), mid stage (MS), or advanced stage (AS) HD. Data were collected via three questionnaires: a case report form, completed by physicians who collected health care resource use associated with HD to compute direct medical cost, and optional patient and caregiver questionnaires, which