Baseline Neuropsychological Characteristics of Adolescents and Young Adults with Down Syndrome Who Participated in Two Clinical Trials of the Drug Memantine

Abstract

Background/Objectives: Down syndrome (DS) is a neurodevelopmental and neurodegenerative disorder typically caused by trisomy 21. We recently concluded a two-site (Ohio, USA and São Paulo, Brazil), phase-2, randomized trial to evaluate the efficacy, tolerability, and safety of the drug memantine in enhancing cognitive abilities of adolescents and young adults with DS. This trial was a follow-up study to a pilot trial performed in Colorado, USA. Results of these two clinical trials have been published elsewhere. Here, we present a comparative analysis of the baseline neuropsychological assessments at the three sites of these two studies, including their psychometric properties, and an account of the considerations involved in the test battery design. We compared test results in the different sites as a way of evaluating the replicability and generalizability of the test results. The distribution of the test results at each site was analyzed and combined when no differences were detected between the mean values of these results. We used post-treatment data from the placebo arms of these studies to quantify test–retest reliability. Results: Most measures had comparable mean values across test sites, and had good-to-excellent feasibility, few floor effects, and good-to-excellent test–retest reliability. A few measures, however, were deemed unsuitable for use in future studies. Conclusions: This study demonstrated remarkable consistency of results across studies in two countries with significantly different cultures and levels of socioeconomic development, which provides supporting evidence for the future design and implementation of similar multicenter, international clinical studies involving participants with DS.