Leucovorin for the Treatment of Language Impairment in Children With Autism Spectrum Disorder

Inclusion Criteria: * Boys and girls ≥ 5 years and \< 17 years 5 months of age; * Weight ≥ 15 kg; * DSM-5 diagnosis of Autism Spectrum Disorder as established by clinical assessment, corroborated by the Social Communication Questionnaire and the Autism Diagnostic Observational Schedule. * A score \< 80 on the Core Language score of the Clinical Evaluation of Language Fundamentals -4 (CELF)- 4 or the Second Edition of the CELF-Preschool test (CELF-P). * Current Clinical Global Impression Severity score ≥ 4 on ASD + communication delay. * IQ at least 40 as measured by the Leiter-3 or mental age at least 18 months as measured on the Receptive Language Scale of the Mullen. * Stable educational plan (one month) with no planned changes in the intensity of treatment for 12 weeks. (Otherwise eligible subjects with anticipated changes in their school program in the near term will be invited to return when the transition has been accomplished. * Stable speech therapy program in the community (one month) with no planned changes for 12 weeks. * English is spoken in the home and at least one parent is able to read, write and speak English. * Stable medication (no changes in past 6 weeks and no planned changes for the next 6 months (duration of the study). Exclusion Criteria: * IQ below 40 as measured by the Leiter-3 or below a mental age of 18 months on the Receptive Language Scale of Mullen. (N.B. subjects who test below 18 months of age, but are otherwise eligible, may be enrolled fo…