Memantine for the Treatment of Social Deficits in Youth With Disorders of Impaired Social Interactions

Inclusion Criteria: * Male \& female subjects ages 8-18 years (inclusive). * Diagnostic Statistical Manual (DSM)-5 Autism Spectrum Disorder (ASD) diagnostic criteria as established by clinical diagnostic interview * At least moderate severity of social impairment as measured by a total raw score of ≥85 on the parent/guardian-completed Social Responsiveness Scale-Second Edition (SRS-2)14 and a score of ≥4 on the clinician-administered Clinical Global Impression-Severity scale (CGI-S)17. Exclusion Criteria: * IQ ≤70 based on the Wechsler Abbreviated Scale of Intelligence-II (WASI-II) Vocabulary and Matrix Reasoning subtests * Impaired communicative speech * Subjects currently treated with the following medications (known to impact glutamate levels): Lamotrigine, Amantadine, N-acetylcysteine, D-cycloserine * Subjects treated with a psychotropic medication not listed above on a dose that has not been stable for at least 4 weeks prior to study baseline. * Co-administration of drugs that compete with memantine for renal elimination using the same renal cationic system, including hydrochlorothiazide, triamterene, metformin, cimetidine, ranitidine, quinidine, and nicotine * Initiation of a new psychosocial intervention within 30 days prior to randomization. * Subjects who are pregnant and/or nursing. * Subjects with a history of non-febrile seizures without a clear and resolved etiology. * Subjects with a history of or a current liver or kidney disease. * Clinically unstable psychiatric conditions or judged to be at serious suicidal risk. * Subjects who meet on the Kiddie Schedule for Affective Disorders and Schizophrenia (K-SADS-E) for alcohol or drug dependence or abuse. If the subject has a recent history of substance abuse, there will be a two-week washout period before initiating the trial as an added precaution. There are no known safety issues relating to memantine and recent history of substance abuse. * Serious, stable or unstable systemic illness including hepatic, renal, gastroenterological, respiratory, cardiovascular (including ischemic heart disease), endocrinologic, neurologic, immunologic, or hematologic disease. * Subjects with severe hepatic impairment (LFTs \> 3 times ULN). * Subjects with genitourinary conditions that raise urine pH (e.g., renal tubular acidosis, severe infection of the urinary tract). * Known hypersensitivity to memantine. * Severe allergies or multiple adverse drug reactions. * A history of intolerance or adequate exposure to memantine, as determined by the clinician. * Investigator and his/her immediate family defined as the investigator's spouse, parent, child, grandparent, or grandchild.