Clinical Research Directory

Inclusion Criteria: * Cytogenetically documented Trisomy 21 or Complete Unbalanced Translocation of Chromosome 21. Mosaic Trisomy 21 and partial translocations will be excluded from the study * No pregnancy by serum testing at screening. Females of child-bearing potential, sexually active must be practicing a reliable method of birth control. Urine pregnancy tests will be done at the 2 follow-up medical visits * Laboratory findings within normal limits or judged clinically insignificant at baseline * Vital signs within normal limits for age. Stable, medically treated hypotension will be allowed * ECG must demonstrate predominately normal sinus rhythm. Minor abnormalities documented as clinically insignificant will be allowed * Participants and their authorized representatives will provide written informed consent * Participants who have received any experimental drug for Down syndrome must undergo a washout * All participants must: Be in general good health as judged by the investigators; Be able to swallow oral medication; Have a reliable caregiver or family member who agrees to accompany participant to all visits, provide information about the participant as required by the protocol, and ensure compliance with the medication schedule; Be sufficiently proficient in English to reliably complete the study assessments * Age and gender matching participants without Down syndrome, must be: Males or females without Down syndrome aged-matching (within 3 years) participants with Down syndrome whom they are expected to serve as controls Exclusion Criteria: * Participant weighing less than 40 kg * Current psychiatric or neurologic diagnosis other than Down syndrome (e.g., major depressive disorder, schizophrenia, bipolar disorder, autism, Alzheimer disease) * Current treatment with psychotropic drugs * Drug or alcohol abuse or dependence * Significant suicide risk or who would require treatment with electro-convulsive therapy or with psychotropic drugs during the study or who have received treatment with a depot neuroleptic drug within 6 months of entering the study. * Current or expected (within the next 6 months) hospitalization or residence in a skilled nursing facility (may reside in group homes or other residential settings with no skilled nursing) * Active or clinically significant conditions affecting absorption, distribution, or metabolism of study drug (e.g. inflammatory bowel disease or celiac disease) * Significant allergies to or other significant intolerance of memantine therapy, its ingredients, or with contraindications to memantine therapy as stated in the prescribing information * Participants who are expected to require general anesthetics during the course of the study * Presence or recent history of seizure disorder (\< 3 years). * Clinically significant and/or clinically unstable systemic disease. (Those with controlled hypothyroidism must be on a stable dose of medication for at least 3 months prior to screening and have normal serum T-4 and TSH at screening; and those with controlled diabetes mellitus must have an HbA1c of \< 8.0% and a random serum glucose value of \< 170 mg/dl) * Severe infections or a major surgical operation within 3 months prior to screening * History of persistent cognitive deficits immediately following head trauma. * Donation of blood or blood products less that 30 days prior to screening, while participating in the study, or four weeks after completion of the study * Inability to comply with the protocol or perform the outcomes measures due to significant hearing or visual impairment or other issues judged relevant by the investigators