Study characteristics.

* not provided ** We used “vitamins” as a category for studies using either folic acid alone or a combination of vitamins, minerals and/or antioxidants. Abbreviations: Down Syndrome (DS), Fragile X Syndrome (FX) and Prader-Willi Syndrome (PW). Gamma-Aminobutyric acid (GABA) agonist, N-metyl-D-aspartat (NMDA) antagonist, Acetylcholinesterase Inhibitor (AchEI). Descriptive features of the studies included in the placebo controlled trials of the meta-analysis.