a daily matching placebo administered over 16 weeks

Semantic Fluency Score. Definition: The Semantic Fluency Score is the number of words a person can produce given a category, including naming (1) Animal names, (2) Fruit names, (3) Boy names, (4) Girl names, and (5) Vegetable names. Construct Measured: Working memory and verbal initiation. Scale Range: The Semantic Fluency Score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance on working memory tasks. Change Calculation Details: Compares change in working memory performance from visit 2 (week 0) where patients named fruit names to the weighted average of visits 5 (week 12) & 6 (week 15) where patients named girl names and vegetable names respectively for the citalopram versus placebo cohort.

Full Scale Name: The Symbol Digit Modalities Test (SDMT). Definition: The SDMT screens for organic cerebral dysfunction by having the examinee use a reference key to pair specific numbers with given geometric figures in 90 seconds. Construct Measured: Attention, processing speed, and working memory. SDMT Scale Range: Raw scores may range from 0 to 110, where lower scores indicate poorer performance. Change Calculation Details: Compares change in performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort.

Full Scale Name: The Verbal Fluency Score (VFC). Definition: The VFC is the number of words a person can produce given a letter, including (1) Naming words that start with F, A, and S; (2) naming words that start with K, W, and R; (3) naming words that start with V, I, and P; (4) naming words that start with O, G, and B; (5) naming words that start with E, N, and T; and (6) naming words that start with J, C, and S. Construct Measured: Verbal initiation and flexibility. Scale Range: The Verbal Fluency Composite Score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance. Change Calculation Details: Compares change in verbal initiation and flexibility from visit 2 (week 0) where patients named words starting with O, G, and B to the weighted average of visits 5 (week 12) and 6 (week 15) where patients named words starting with E, N, and T, and J, C, and S respectively for the citalopram versus placebo cohort.

Full Scale Name: Stroop Interference subtest from The Stroop Color and Word Test. Definition: Participants are asked to name the ink color in which a word is printed when the word itself (which is irrelevant to the task) is the name of a different color rather than the same color. For example, participants may be asked to say "red" to the word blue printed in red ink. Constructs Measured: Selective attention, response inhibition, cognitive flexibility, and processing speed. Scale Range: The Stroop Interference score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance. Change Calculation Details: Compares change in attention and processing speed performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) and 6 (week 15) for the citalopram versus placebo cohort.

Full Scale Name: Trail Making Test Part B (TMT-B). Definition: The TMT-B test requires participants to "connect-the-dots" of 25 consecutive targets on a sheet of paper where the subject alternates between numbers and letters, going in both numerical and alphabetical order. Constructs Measured: Attention, set shifting, and processing speed. Scale range: The TMT-B score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance. Change Calculation Details: Compares change in attention and processing speed performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) and 6 (week 15) for the citalopram versus placebo cohort.

Full Scale Name: Hamilton Rating Scale for Depression (HAM-D). Definition: The Hamilton Rating Scale for Depression is a clinician-administered multiple item questionnaire used to provide an indication of depression. Construct Measured: Depression. HAM-D Score Range: Raw scores may range from 0 to 54, where higher scores indicate worsening mood. Change Calculation Details: Compares change in mood from screening (intake visit) to visit 6 (week 15) for the citalopram versus placebo cohort.

Full Scale Name: The Total Functional Capacity (TFC) subscale from the Unified Huntington's Disease Rating Scale (UHDRS). Definition: The TFC is a score that classifies five stages of Huntington's Disease and five levels of function in the domains of workplace, finances, domestic chores, activities of daily living and requirements for unskilled or skilled care. Construct Measured: Activities of Daily Living. Scale Range: The TFC score ranges from 0 to 13, where lower scores indicate poorer performance in activities of daily living. Change Calculation Details: Compares change in TFC performance from Baseline (week -4) to the weighted average of visits 4 (week 6) and 6 (week 15) for the citalopram versus placebo cohort.

Full Scale Name: Hamilton Rating Scale for Depression (HAM-D). Definition: The Hamilton Rating Scale for Depression is a clinician-administered multiple item questionnaire used to provide an indication of depression. Construct Measured: Depression. HAM-D Score Range: Raw scores may range from 0 to 54, where higher scores indicate worsening mood. Change Calculation Details: This analysis was restricted to a subgroup and, accordingly, does not reflect the total number of participants as reported in the Participant Flow. This analysis compares change in mood from screening (intake visit) to visit 6 (week 15) for the citalopram versus placebo cohort.

Full Scale Name: Letter Number Sequencing (LNS) subtest from the Wechsler Adult Intelligence Scale (WAIS) third edition. Definition: LNS is a task that requires the reordering of an initially unordered set of letters and numbers. Construct Measured: Working memory. LNS Score Range: Raw scores may range from 0 to 21, where lower scores indicate poorer performance in working memory. Change Calculation Details: Compares change in working memory performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model controlling for practice effects comparing visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort

Semantic Fluency Score. Definition: The Semantic Fluency Score is the number of words a person can produce given a category, including naming (1) Animal names, (2) Fruit names, (3) Boy names, (4) Girl names, and (5) Vegetable names. Construct Measured: Working memory and verbal initiation. Scale Range: The Semantic Fluency Score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance on working memory tasks. Change Calculation Details: Compares change in working memory performance from visit 2 (week 0) where patients named fruit names to the weighted average of visits 5 (week 12) & 6 (week 15) where patients named girl names and vegetable names respectively for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model controlling for practice effects comparing visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: The Symbol Digit Modalities Test (SDMT). Definition: The SDMT screens for organic cerebral dysfunction by having the examinee use a reference key to pair specific numbers with given geometric figures in 90 seconds. Construct Measured: Attention, processing speed, and working memory. SDMT Scale Range: Raw scores may range from 0 to 110, where lower scores indicate poorer performance. Change Calculation Details: Compares change in performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model controlling for practice effects comparing visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: The Verbal Fluency Score (VFC). Definition: The VFC is the number of words a person can produce given a letter, including (1) Naming words that start with F, A, and S; (2) naming words that start with K, W, and R; (3) naming words that start with V, I, and P; (4) naming words that start with O, G, and B; (5) naming words that start with E, N, and T; and (6) naming words that start with J, C, and S. Construct Measured: Verbal initiation and flexibility. Scale Range: The Verbal Fluency Composite Score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance. Change Calculation Details: Compares change in verbal initiation and flexibility from visit 2 (week 0) where patients named words starting with O, G, and B to the weighted average of visits 5 (week 12) and 6 (week 15) where patients named words starting with E, N, and T, and J, C, and S respectively for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model controlling for practice effects comparing visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: Stroop Interference subtest from The Stroop Color and Word Test. Definition: Participants are asked to name the ink color in which a word is printed when the word itself (which is irrelevant to the task) is the name of a different color rather than the same color. For example, participants may be asked to say "red" to the word blue printed in red ink. Constructs Measured: Selective attention, response inhibition, cognitive flexibility, and processing speed. Scale Range: The Stroop Interference score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance. Change Calculation Details: Compares change in attention and processing speed performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) and 6 (week 15) for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model controlling for practice effects comparing visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: Trail Making Test Part B (TMT-B). Definition: The TMT-B test requires participants to "connect-the-dots" of 25 consecutive targets on a sheet of paper where the subject alternates between numbers and letters, going in both numerical and alphabetical order. Constructs Measured: Attention, set shifting, and processing speed. Scale range: The TMT-B score ranges from -5 to +5 on a standardized (Z) score scale, where lower scores indicate poorer performance. Change Calculation Details: Compares change in attention and processing speed performance from visit 2 (week 0) to the weighted average of visits 5 (week 12) and 6 (week 15) for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model controlling for practice effects comparing visit 2 (week 0) to the weighted average of visits 5 (week 12) & 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: Hamilton Rating Scale for Depression (HAM-D). Definition: The Hamilton Rating Scale for Depression is a clinician-administered multiple item questionnaire used to provide an indication of depression. Construct Measured: Depression. HAM-D Score Range: Raw scores may range from 0 to 54, where higher scores indicate worsening mood. Change Calculation Details: Compares change in mood from screening (intake visit) to visit 6 (week 15) for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model comparing screening (intake visit) to Visit 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: The Total Functional Capacity (TFC) subscale from the Unified Huntington's Disease Rating Scale (UHDRS). Definition: The TFC is a score that classifies five stages of Huntington's Disease and five levels of function in the domains of workplace, finances, domestic chores, activities of daily living and requirements for unskilled or skilled care. Construct Measured: Activities of Daily Living. Scale Range: The TFC score ranges from 0 to 13, where lower scores indicate poorer performance in activities of daily living. Change Calculation Details: Compares change in TFC performance from Baseline (week -4) to the weighted average of visits 4 (week 6) and 6 (week 15) for the citalopram versus placebo cohort.

Intention to treat analysis was performed using a mixed linear model comparing baseline (week -4) to the weighted average of Visits 4 (week 6) & 6 (week 15) for the citalopram versus placebo cohort

Full Scale Name: Hamilton Rating Scale for Depression (HAM-D). Definition: The Hamilton Rating Scale for Depression is a clinician-administered multiple item questionnaire used to provide an indication of depression. Construct Measured: Depression. HAM-D Score Range: Raw scores may range from 0 to 54, where higher scores indicate worsening mood. Change Calculation Details: This analysis was restricted to a subgroup and, accordingly, does not reflect the total number of participants as reported in the Participant Flow. This analysis compares change in mood from screening (intake visit) to visit 6 (week 15) for the citalopram versus placebo cohort.

This analysis was restricted to a subgroup and, accordingly, does not reflect the total number of participants as reported in the Participant Flow. This analysis compares change in mood from screening (intake visit) to visit 6 (week 15) for the citalopram versus placebo cohort.

Matching daily placebo