Participants with IDDD failures were reported.

FPSS is a sanfilippo-specific disability assessment which assesses motor function, expressive/speech language, and cognitive function on a 0 to 3 point scale. A score of 3 points is assigned for normal function, 2 points for beginning of regression, 1 point for severe level of regression, and 0 points for lost skills. The total disability score (TDS) is the average (0-3) of the motor skills (MS), speech abilities (SA), and cognitive function (CF) scores. Lower scores indicate developmental regression.

SBRS a parent-scored behavioral inventory measuring: comprehensive language skills, expressive language skills, tantrums, mood and emotions, and other behaviors not otherwise classified. Subscale items are scored 0=Never, 1=Occasionally(5-10%), 2=Sometimes (25%), 3=About half the time, 4=Often(75%), 5=Almost always (90%), 6=Always. Summary scores are the sum of responses within a given domain. Higher values = undesirable behavior. Total score range listed below with the abbreviations. Current Communication (CC)(0-42), Past Communication (PC)(0-42), Orality (0-36), Body Movements (BM)(0-30), Interaction With Objects (IWO)(0-24), Activity And Routines (AAR)(0-36), Emotional Function (EF)(0-18), Safety-consciousness (SC)(0-18), Fearfulness (0-36), Social Interaction (SI)(0-36), Eye Contact (EC)(0-18), Emotional Engagement (EE)(0-18), Comfort Seeking (CS)(0-30), Attention (0-18), Self-control/Compliance (SCC)(0-18), Mood, Anger/Aggression (MAA)(0-42), Self-gratification (SG)(0-24).

VABS-II measures adaptive behaviors, including the ability to cope with environmental changes, to learn new everyday skills, and to demonstrate independence. It is an instrument that supports the diagnosis of intellectual and developmental disabilities in participants. This test measures 5 key domains: communication, daily living skills, socialization, motor skills, and the adaptive behavior composite (a composite of the other four domains). Scoring is 'Usually' = 2, 'Sometimes'/Partially' = 1 or 'Never' = 0. The raw scores will be converted to domain standard scores (mean 100, SD 15). Higher scores indicate undesirable behavior. The Overall DQ score was calculated from the mean age-equivalent score obtained by averaging out the age equivalent scores for all the sub-domains except for Gross and Fine motor skills.

Movement Assessment Battery for Children, Second Edition (MABC-II) was to be used to identify, describe and guide the treatment of motor impairment in children from 3.0 to 16:11 years of age. As per statistical analysis plan, the outcome was to be assessed only if greater than (>) 50 percent (%) of participants were available for the evaluation.

CHQ-PF50 which was designed to measure the physical and psychosocial well-being of children 5 years to 18 years of age, consists of 13 health concepts including 11 multi-item and 2 single item scales: Physical Function (PF), Role/Social-Emotional/Behavioral (REB), Role/Social-Physical (RP), bodily pain (BP), General Behavior (BE), Mental Health (MH), Self Esteem (SE), General Health Perceptions (GH), Change in Health (CH), Parental Impact-Emotional (PE), Parental Impact-Time (PT), Family Activities (FA), and Family Cohesion (FC). Transformed scores for all subscales range from 0 to 100, with a higher score indicating better health. Physical and Psychosocial Summary measures (SM) were scored with the use of norm-based methods that standardize the scores to a mean (± Standard Deviation) of 50 ± 10 on the basis of an assessment of the general United States population. Higher values represent better health.

ITQOL is a generic, validated health status measure for children aged 2 months up to 5 years, including items and scales to measure aspects of physical functioning, development, pain, mood, behavior, general health and impact on parents. The ITQOL consists of 97 items that are scored, summed, and transformed on a scale from 0 (worst health) to 100 (best health). The score range for all individual subscales is 0 (worst health) to 100 (best health). Abbreviation: Overall Health (OH), Physical Abilities (PA), Growth And Development (GAD), Bodily Pain (BP), Temperament And Moods (TAM), General Behavior (GEB), Global Behavior (GLB), Getting Along (GA), General Health Perceptions (GHP), PI-Emotion (PIE), PI-Time (PIT), Family Cohesion (FC).

CHQ-CF87 form was designed to be a self-report for participants 10 years and older. It consists of 87 questions and contains the same scales as the PF-50, (with the omission of the parental impact scales and there are no psychosocial and physical summary scores derived). As per statistical analysis plan, the outcome was to be assessed only if greater than (>) 50 percent (%) of participants were available for the evaluation.

Children's sleep habits rating scale consisting of 35 item parent questionnaire sleep screening tool. Items are scored on a 3-point scale from 1 (rarely) to 3 (usually) with a Total Sleep Disturbance score (TSDS) ranging from 35-105. Eight subscale scores are totaled to create the TSDS. The subscales are: Bedtime Resistance (BR)(6 items, score = 6-18), Sleep Duration (SD)(3 items, score = 3-9), Parasomnias (P)(7 items, score = 7-21), Sleep Disordered Breathing (SDB)(3 items, score = 3-9), Night Waking (NW)(3 items, score = 3-9), Daytime Sleepiness (DS)(8 items, score = 8-24), Sleep Anxiety (SA)(4 items, score = 4-12), and Sleep Onset Delay (SOD)(1 item, score = 1-3). The questionnaire was designed for children aged 4 through 12 years. A higher score is indicative of more disturbed sleep.

Cerebrospinal fluid samples were collected from participants through an implanted IDDD or via lumbar puncture (LP) immediately prior to each administration of HGT-1410.

Levels of heparan sulfate and its derivatives were evaluated using the proprietary Sensi-Pro (SP) high-performance liquid chromatography (HPLC) based assay. Abbreviation: SP Total Heparan Sulfate (SPTHS), SP Non-Reducing End Assay (SPNREA),

Brain MRI was measured for grey matter volume (GMV) , white matter volume (WMV) and Intracranial cerebrospinal fluid Volume (ICSFV) (Ventricles + Additional CSF Space).

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Mean ABR air and bone conduction threshold were assessed. Mean ABR bone conduction threshold was not possible to be reported as there was insufficient data to be analysed.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. The Inter-peak Latencies (IPL) were calculated by subtracting the absolute latencies (AL). The Inter-aural Latencies (IAL) were calculated by subtracting the absolute wave V latencies of the right and left ear. IAL, IPL and AL were reported. Abbreviation: Right Ear (RE), Left Ear (LE), Wave (W), Wave V (WV)

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR amplitudes by left ear (LE) and right ear (RE) were reported.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR amplitudes(A), log-transformed amplitudes (LTA), square-root transformed amplitudes (STA) by left ear (LE) and right ear (RE) wave V/I in ratio was reported.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR log-transformed latencies (LTL) by left and right ear were reported.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR log-transformed amplitudes (LTA) by left and right ear were reported.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR square-root transformed latency (STL) by left and right ear were reported.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR square-root transformed amplitude (STA) by left and right ear were reported.

HGT-1410/rhHNS 45 mg dose every 14 [±2 days] for a monthly total dose of 90 mg via an IDDD for 6 months.

Total of all reporting groups

HGT-1410/rhHNS 45 mg monthly via an IDDD (every 28 [±7 days]) for a total of 6 months.

HGT-1410/rhHNS 45 mg dose every 14 [±2 days] for a monthly total dose of 90 mg via an IDDD for 6 months.

An adverse event (AE) was defined as any untoward medical occurrence in a clinical investigation participant administered as a pharmaceutical product that did not necessarily have a causal relationship with this treatment. A serious adverse event (SAE) was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged in-patient hospitalization; life threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly. Treatment-emergent AEs (TEAEs) were defined as all adverse events (AEs) from the time of the surgery for IDDD implantation to the last follow up contact, 30 (±7) days after the end of study (EOS) procedures.

Safety population.

Participants with positive, negative and missing status were reported.

Intent to treat (ITT) population was defined as all enrolled participants who received at least 1 dose (full or partial) of study drug.

Participants with positive, negative and missing status were reported.

ITT population

Participants with IDDD failures were reported.

ITT population.

BSID-III was used to assess the motor (fine and gross), language (receptive and expressive), and cognitive development of infants and toddlers. This measure consists of a series of developmental play tasks. Raw scores of successfully completed items are converted to scale scores and to composite scores. The mean composite score is 100 and the standard deviation (SD) is 15.Higher scores are indicative of decreased development. KABC-II was an individually administered measure of the processing and reasoning abilities of children and adolescents between the ages of 3 and 18 years and is an alternative to BSID-III. BSID-III DQ score was based on the Cognitive domain. The DQ score was calculated from the data obtained from either BSID-III/KABC-II mental age equivalent of the child in months divided by the calendar age in months (multiplied by 100 to give percentage points).

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

FPSS is a sanfilippo-specific disability assessment which assesses motor function, expressive/speech language, and cognitive function on a 0 to 3 point scale. A score of 3 points is assigned for normal function, 2 points for beginning of regression, 1 point for severe level of regression, and 0 points for lost skills. The total disability score (TDS) is the average (0-3) of the motor skills (MS), speech abilities (SA), and cognitive function (CF) scores. Lower scores indicate developmental regression.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

SBRS a parent-scored behavioral inventory measuring: comprehensive language skills, expressive language skills, tantrums, mood and emotions, and other behaviors not otherwise classified. Subscale items are scored 0=Never, 1=Occasionally(5-10%), 2=Sometimes (25%), 3=About half the time, 4=Often(75%), 5=Almost always (90%), 6=Always. Summary scores are the sum of responses within a given domain. Higher values = undesirable behavior. Total score range listed below with the abbreviations. Current Communication (CC)(0-42), Past Communication (PC)(0-42), Orality (0-36), Body Movements (BM)(0-30), Interaction With Objects (IWO)(0-24), Activity And Routines (AAR)(0-36), Emotional Function (EF)(0-18), Safety-consciousness (SC)(0-18), Fearfulness (0-36), Social Interaction (SI)(0-36), Eye Contact (EC)(0-18), Emotional Engagement (EE)(0-18), Comfort Seeking (CS)(0-30), Attention (0-18), Self-control/Compliance (SCC)(0-18), Mood, Anger/Aggression (MAA)(0-42), Self-gratification (SG)(0-24).

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

VABS-II measures adaptive behaviors, including the ability to cope with environmental changes, to learn new everyday skills, and to demonstrate independence. It is an instrument that supports the diagnosis of intellectual and developmental disabilities in participants. This test measures 5 key domains: communication, daily living skills, socialization, motor skills, and the adaptive behavior composite (a composite of the other four domains). Scoring is 'Usually' = 2, 'Sometimes'/Partially' = 1 or 'Never' = 0. The raw scores will be converted to domain standard scores (mean 100, SD 15). Higher scores indicate undesirable behavior. The Overall DQ score was calculated from the mean age-equivalent score obtained by averaging out the age equivalent scores for all the sub-domains except for Gross and Fine motor skills.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

Movement Assessment Battery for Children, Second Edition (MABC-II) was to be used to identify, describe and guide the treatment of motor impairment in children from 3.0 to 16:11 years of age. As per statistical analysis plan, the outcome was to be assessed only if greater than (>) 50 percent (%) of participants were available for the evaluation.

This outcome measure was not analyzed as it does not meet the pre-specified SAP criteria (outcome was to be assessed only if greater than (>) 50 percent (%) of participants were available for the evaluation).

CHQ-PF50 which was designed to measure the physical and psychosocial well-being of children 5 years to 18 years of age, consists of 13 health concepts including 11 multi-item and 2 single item scales: Physical Function (PF), Role/Social-Emotional/Behavioral (REB), Role/Social-Physical (RP), bodily pain (BP), General Behavior (BE), Mental Health (MH), Self Esteem (SE), General Health Perceptions (GH), Change in Health (CH), Parental Impact-Emotional (PE), Parental Impact-Time (PT), Family Activities (FA), and Family Cohesion (FC). Transformed scores for all subscales range from 0 to 100, with a higher score indicating better health. Physical and Psychosocial Summary measures (SM) were scored with the use of norm-based methods that standardize the scores to a mean (± Standard Deviation) of 50 ± 10 on the basis of an assessment of the general United States population. Higher values represent better health.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ITQOL is a generic, validated health status measure for children aged 2 months up to 5 years, including items and scales to measure aspects of physical functioning, development, pain, mood, behavior, general health and impact on parents. The ITQOL consists of 97 items that are scored, summed, and transformed on a scale from 0 (worst health) to 100 (best health). The score range for all individual subscales is 0 (worst health) to 100 (best health). Abbreviation: Overall Health (OH), Physical Abilities (PA), Growth And Development (GAD), Bodily Pain (BP), Temperament And Moods (TAM), General Behavior (GEB), Global Behavior (GLB), Getting Along (GA), General Health Perceptions (GHP), PI-Emotion (PIE), PI-Time (PIT), Family Cohesion (FC).

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

CHQ-CF87 form was designed to be a self-report for participants 10 years and older. It consists of 87 questions and contains the same scales as the PF-50, (with the omission of the parental impact scales and there are no psychosocial and physical summary scores derived). As per statistical analysis plan, the outcome was to be assessed only if greater than (>) 50 percent (%) of participants were available for the evaluation.

This outcome measure was not analyzed as it does not meet the pre-specified SAP criteria (outcome was to be assessed only if greater than (>) 50 percent (%) of participants were available for the evaluation).

Children's sleep habits rating scale consisting of 35 item parent questionnaire sleep screening tool. Items are scored on a 3-point scale from 1 (rarely) to 3 (usually) with a Total Sleep Disturbance score (TSDS) ranging from 35-105. Eight subscale scores are totaled to create the TSDS. The subscales are: Bedtime Resistance (BR)(6 items, score = 6-18), Sleep Duration (SD)(3 items, score = 3-9), Parasomnias (P)(7 items, score = 7-21), Sleep Disordered Breathing (SDB)(3 items, score = 3-9), Night Waking (NW)(3 items, score = 3-9), Daytime Sleepiness (DS)(8 items, score = 8-24), Sleep Anxiety (SA)(4 items, score = 4-12), and Sleep Onset Delay (SOD)(1 item, score = 1-3). The questionnaire was designed for children aged 4 through 12 years. A higher score is indicative of more disturbed sleep.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

Cerebrospinal fluid samples were collected from participants through an implanted IDDD or via lumbar puncture (LP) immediately prior to each administration of HGT-1410.

ITT population.

Levels of heparan sulfate and its derivatives were evaluated using the proprietary Sensi-Pro (SP) high-performance liquid chromatography (HPLC) based assay. Abbreviation: SP Total Heparan Sulfate (SPTHS), SP Non-Reducing End Assay (SPNREA),

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

Brain MRI was measured for grey matter volume (GMV) , white matter volume (WMV) and Intracranial cerebrospinal fluid Volume (ICSFV) (Ventricles + Additional CSF Space).

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Mean ABR air and bone conduction threshold were assessed. Mean ABR bone conduction threshold was not possible to be reported as there was insufficient data to be analysed.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. The Inter-peak Latencies (IPL) were calculated by subtracting the absolute latencies (AL). The Inter-aural Latencies (IAL) were calculated by subtracting the absolute wave V latencies of the right and left ear. IAL, IPL and AL were reported. Abbreviation: Right Ear (RE), Left Ear (LE), Wave (W), Wave V (WV)

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR amplitudes by left ear (LE) and right ear (RE) were reported.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR amplitudes(A), log-transformed amplitudes (LTA), square-root transformed amplitudes (STA) by left ear (LE) and right ear (RE) wave V/I in ratio was reported.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR log-transformed latencies (LTL) by left and right ear were reported.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR log-transformed amplitudes (LTA) by left and right ear were reported.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR square-root transformed latency (STL) by left and right ear were reported.

ITT population.Here, n = participants evaluable for specified category for each arm, respectively.

ABR assessments were to be conducted under anesthesia and measured the electrical response evoked by acoustic stimuli as sound is processed along the auditory pathway. Data for change from baseline in ABR square-root transformed amplitude (STA) by left and right ear were reported.

ITT population. Here, n = participants evaluable for specified category for each arm, respectively.

HGT-1410/rhHNS 45 mg monthly via an IDDD (every 28 [±7 days]) for a total of 6 months.

HGT-1410/rhHNS 45 mg dose every 14 [±2 days] for a monthly total dose of 90 mg via an IDDD for 6 months.