Exclusion Criteria:

•     Life expectancy of less than 18 months
•    Pre-existing conditions:
•        Any contraindication or allergy to study drug (memantine or placebo)
•        Intractable seizures while on adequate anticonvulsant therapy, defined as more than one seizure per month for the past 2 months or since initiating anticonvulsant therapy
•        History of neurodevelopmental disorder such as Down syndrome, Fragile X, William's Syndrome, intellectual disability (presumed intelligence quotient [IQ] < 70), etc
•        Co-morbid systemic illnesses, psychiatric conditions, social situations, or other severe concurrent disease which, in the judgment of the investigator, would make the patient inappropriate for entry into this study or interfere significantly with the proper assessment of safety and toxicity of the prescribed regimens or would limit compliance with the study requirements
•        Patients with a motor, visual, or auditory condition that precludes participation in computerized neurocognitive assessments
•        Patients with any medical condition or taking medications that lead to alterations of urine pH towards the alkaline condition (e.g., renal tubular acidosis, carbonic anhydrase inhibitors, sodium bicarbonate)
•    Personal history of prior cranial or craniospinal radiotherapy is not allowed
•        Note: Prior anti-cancer therapy including surgery, chemotherapy, targeted agents are allowed as per standard of care clinical treatment guidelines
•    Female patients who are pregnant are excluded since fetal toxicities and teratogenic effects have been noted for the study drug. A pregnancy test is required for female patients of childbearing potential
•    Lactating females who plan to breastfeed their infants
•    Sexually active patients of reproductive potential who do not agree to use an effective contraceptive method for the duration of their study participation
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