Memantine in Adult Autism Spectrum Disorder

Inclusion criteria * Participant is currently in treatment in the Johns Hopkins Bayview Medical Center (JHBMC) * Participant has a diagnosis of: * Autistic Disorder * Asperger's Disorder * Pervasive Developmental Disorder (PDD) NOS * Participant meets one of the following criteria: * CGI-S \>= 4 (CGI-S: \_\_\_\_\_\_\_\_) * Participant has the following problematic behaviors (at least one) that might be expected to benefit from memantine: 1. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 2. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 3. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Exclusion criteria The patient meets none of the following criteria (mark if absent): * Active seizures (Patients with a history of seizures, who have been seizure-free on an antiepileptic regimen for six months or more would be eligible). * Rett's Syndrome or Childhood Disintegrative Disorder * Active treatment with an acetylcholinesterase inhibitor * Prior or current treatment with memantine * Current treatment with lamotrigine * Genetic, metabolic or degenerative disorder (excepting Fragile X). * Brain malformation or known severe brain trauma * Pregnancy or breastfeeding * Glomerular Filtration Rate (GFR) \< 30 mL/min