An Open-Label Phase II Feasibility Study for the Use of Ublituximab in Adults With Down Syndrome Regression Disorder

Safety will be evaluated by the incidence, type, severity (graded per CTCAE v5.0), and relationship of treatment-emergent adverse events (AEs) occurring after the first dose of ublituximab. Tolerability will be assessed by the proportion of participants completing both doses and follow-up without dose modifications, interruptions, or discontinuation due to AEs.

Change from baseline in adaptive functioning measured by the Vineland Adaptive Behavior Scales, Third Edition (VABS-3), including communication, daily living skills, socialization, and maladaptive behavior domains as reported by caregivers.

Change from baseline in catatonia symptoms measured by the Bush-Francis Catatonia Rating Scale (BFCRS), with decreases in total score indicating improvement in symptom severity.

0 (no catatonia) - 45 (Severe Catatonia)

Change from baseline in neuropsychiatric symptom burden as measured by the Neuropsychiatric Inventory Questionnaire (NPI-Q), a caregiver-reported assessment of symptom frequency and severity across behavioral domains.

Change from baseline in time (seconds) required to complete the Timed 25-Foot Walk (T25-FW), reflecting gait speed and motor function, with decreased time indicating improvement.

Change from baseline in global clinical status assessed using the Clinician Global Impression of Change-Down Syndrome (CGIC-DS), a Down syndrome-adapted clinician-rated instrument. The Baseline version generates a Clinical Global Impression-Severity (CGI-S) rating to assess overall illness severity, and the Follow-up version generates a Clinical Global Impression-Improvement (CGI-I) rating to assess clinical change relative to baseline. CGI-S scores range from 1 (normal, not at all ill) to 7 (among the most extremely ill), while CGI-I scores range from 1 (very much improved) to 7 (very much worse). Assessments will be conducted at Baseline, Week 12, and Week 24.

Change from baseline in global clinical status measured using CGI-S and CGI-I ratings derived from the Clinician Global Impression of Change-Down Syndrome (CGIC-DS). CGI-S assesses overall illness severity, and CGI-I assesses improvement or worsening relative to baseline. Assessments will be conducted at Baseline, Week 12, and Week 24. Lower CGI-S scores indicate reduced illness severity, and lower CGI-I scores indicate greater clinical improvement.

Change from baseline in participant quality of life measured by the Pediatric Quality of Life Inventory (PedsQL) Parent Report. This caregiver-reported assessment evaluates health-related quality of life across physical functioning, emotional functioning, social functioning, and work/studies functioning domains. Higher scores indicate better quality of life and functional status. Assessments will be conducted at Baseline, Week 12, and Week 24.

Change from baseline in caregiver and family functioning measured by the Pediatric Quality of Life Inventory Family Impact Module (PedsQL-FIM). This caregiver-reported assessment evaluates the impact of the participant's condition on caregiver well-being and family functioning across physical, emotional, social, cognitive, communication, daily activities, and family relationship domains. Higher scores indicate better caregiver quality of life, improved family functioning, and less negative impact on the family. Assessments will be conducted at Baseline, Week 12, and Week 24.

Change from baseline in communication abilities measured by the Observer-Reported Communication Ability (ORCA) Measure, a caregiver-reported assessment of expressive and receptive communication skills. The ORCA evaluates verbal communication, use of gestures, social communication, requesting, conversation, comprehension, and functional communication abilities in everyday settings. Higher scores indicate greater communication ability and improved functional communication.

Change from baseline in caregiver and family functioning measured by the Pediatric Quality of Life Inventory Family Impact Module (PedsQL-FIM). This caregiver-reported assessment evaluates the impact of the participant's condition on caregiver well-being and family functioning across physical, emotional, social, cognitive, communication, daily activity, and family relationship domains. Higher scores indicate better caregiver and family functioning and lower family burden.

Change from baseline in obsessive-compulsive symptom severity measured by the Children's Yale-Brown Obsessive Compulsive Scale (CY-BOCS), a clinician-administered assessment of obsessions and compulsions. The CY-BOCS evaluates symptom severity across domains including time occupied, interference, distress, resistance, and degree of control. Higher scores indicate greater obsessive-compulsive symptom severity, and decreases in total score indicate improvement.

Change from baseline in peripheral B-cell populations measured by high-sensitivity flow cytometry, including absolute B-cell counts and percentages of CD19+ and CD20+ B cells. Exploratory analyses will evaluate the extent and duration of B-cell depletion following ublituximab treatment and the association between B-cell depletion and clinical outcomes.

Change from baseline in circulating inflammatory cytokine concentrations measured using multiplex immunoassay platforms. Cytokines and related inflammatory biomarkers will be evaluated to characterize immunologic changes associated with ublituximab treatment and Down Syndrome Regression Disorder (DSRD).

Change from baseline in plasma proteomic profiles measured using high-throughput proteomic platforms. Exploratory analyses will identify protein expression patterns associated with DSRD and evaluate molecular changes occurring following ublituximab treatment.

Change from baseline in plasma metabolomic signatures measured using mass spectrometry-based metabolomic analyses. Exploratory analyses will evaluate treatment-associated changes in metabolic pathways and identify biomarkers associated with disease activity and therapeutic response.

Change from baseline in whole-blood transcriptomic signatures, including interferon-related gene expression profiles, measured from RNA biospecimens. Exploratory analyses will characterize molecular pathways associated with DSRD and assess the impact of B-cell depletion therapy on interferon signaling and other transcriptional biomarkers.

Change from baseline in circulating autoantibody profiles measured using high-throughput autoantibody profiling technologies. Exploratory analyses will evaluate changes in autoantibody repertoires following ublituximab treatment and assess associations wi

Change from baseline in plasma biomarkers of neurodegeneration and neuroinflammation, including neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), ubiquitin C-terminal hydrolase L1 (UCHL1), total tau, and other validated biomarkers. Exploratory analyses will evaluate relationships between biomarker changes and clinical outcomes following ublituximab treatment.