An adverse event (AE) means any untoward medical occurrence in a participant or participant administered a pharmaceutical product; the untoward medical occurrence does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product whether or not it is related to the medicinal product. The severity of AEs will be determined per the investigator's assessment.

An AE means any untoward medical occurrence in a participant or participant administered a pharmaceutical product; the untoward medical occurrence does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product whether or not it is related to the medicinal product. Any adverse event related to idursulfase-IT will be reported in this outcome measure.

An AE means any untoward medical occurrence in a participant or participant administered a pharmaceutical product; the untoward medical occurrence does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product whether or not it is related to the medicinal product. Any adverse event related to the IDDD will be reported in this outcome measure.

An AE means any untoward medical occurrence in a participant or participant administered a pharmaceutical product; the untoward medical occurrence does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product whether or not it is related to the medicinal product. Any adverse event related to device surgical procedure will be reported in this outcome measure.

An AE means any untoward medical occurrence in a participant or participant administered a pharmaceutical product; the untoward medical occurrence does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product whether or not it is related to the medicinal product. Any adverse event related to IT administration process will be reported in this outcome measure.

An AE means any untoward medical occurrence in a participant or participant administered a pharmaceutical product; the untoward medical occurrence does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product whether or not it is related to the medicinal product. Any adverse event related to IV elaprase infusion will be reported in this outcome measure.

An AE is any noxious, pathologic, or unintended change in anatomical, physiologic, or metabolic function as indicated by physical signs, symptoms, or laboratory changes occurring in any phase of a clinical study, whether or not considered investigational product-related.

Participants were assessed for clinically significant changes in vital signs like injection (IT) vital signs and regular vital signs (temperature, pulse, blood pressure \[systolic and diastolic\], oxygen saturation, and respiration rate).

Participants were assessed for clinically significant changes in laboratory parameters such as chemistry, hematology, urinalysis and cerebrospinal fluid (CSF) values.

Participants were assessed for clinically significant changes in 12-lead ECG findings (such as heart rate, PR interval, QRS interval, QT interval, and the corrected QT interval).

Idursulfase concentrations in serum were determined using a validated Enzyme -Linked Immunosorbent Assay (ELISA) method. Concentration for Cmax is presented in this endpoint.

The percent change in concentration of GAG in CSF was assessed. GAGs are long sugar chains that are like building blocks for the body's tissues, especially connective tissues like cartilage, skin, and tendons, and play a crucial role in cell signaling and interactions.

The percent change in concentration of GAG in urine was assessed. GAGs are long sugar chains that are like building blocks for the body's tissues, especially connective tissues like cartilage, skin, and tendons, and play a crucial role in cell signaling and interactions.

The DAS-II was used to assess cognitive development in all randomized participants. The GCA standard score of the DAS-II was used to obtain a general measure of cognitive ability. The GCA score represent a score (mean = 100 and standard deviation of 15) on which higher scores indicate a higher level of cognitive ability. The score ranges from 30 to 170. A positive change value indicates improvement in cognitive ability.

An adverse event (AE) is any noxious, pathologic, or unintended change in anatomical, physiologic, or metabolic function as indicated by physical signs, symptoms, and/or laboratory changes occurring in any phase of a clinical trial, and whether or not considered study drug-related. TEAEs were defined as all AEs occurring on or after the first IDDD surgery date or first dose (whichever is earlier) for the participant (whether it is in this extension study or in HGT HIT-045 \[NCT00920647\]) and before the end of the study (EOS) visit (+30 days). For Idursulfase-IT 1 mg+10 mg arm the summary presented includes only the TEAEs that occurred while the participants were assigned to 10 mg.

Number of participants with clinically significant changes in laboratory parameters (chemistry, hematology, urinalysis and CSF values) were collected.

Number of participants with clinically significant changes in 12-lead Electrocardiogram (ECG) findings (heart rate, PR interval, QRS interval, QT interval and the corrected QT interval) were collected.

ITT patient population

White blood cell count in CSF was monitored throughout the study as a way of assessing any potential inflammation of the meninges induced by idursulfase-IT.

Reflects development of anti-idursulfase antibodies post baseline.

Electrocardiogram (ECG) parameters included: heart rate, sinus rhythm, atrial/ventricular hypertrophy, PR, QRS, QT and QTc intervals.