Neuropsychological endpoints for clinical trials in methylmalonic acidemia and propionic acidemia: A pilot study

This pilot study assessed instruments measuring relatively discrete neuropsychological domains to inform the selection of clinical outcome assessments that may be considered for interventional trials in methylmalonic acidemia (MMA) and propionic acidemia (PA).

Tests and questionnaires were selected for their possible relevance to MMA and PA and potential sensitivity to modest changes in functioning and behavior.

Twenty-one patients (<18 years, n = 10;>18 years, n = 11) and/or their caregivers responded to video interviews and paper tests. Language deficits and significant motor deficits in some participants impacted scoring, especially in the verbal and processing speed sections of the Wechsler Intelligence Scale for Children, Fifth Edition (WISC-V) and the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV). However, all participants ≥12 years of age were able to complete the Cookie Theft Picture Task. Thus, verbal discourse remains a potentially useful endpoint for participants in this age group. The Vineland Adaptive Behavior Scales (VABS-3) Adaptive Behavior Composite and Communication Scores confirmed delayed or immature functioning in day-to-day activities in these participants. Significant motor deficits prevented completion of some tests. Computerized processing speed tasks, which require pressing a button or tapping a computer screen, may be easier than writing or checking off boxes on paper in this cohort. Sleep characteristics among MMA participants were within normative ranges of the Child and Adolescent Sleep Checklist (CASC), indicating that this measurement would not provide valuable data in a clinical trial. Despite their challenges, responses to the Metabolic Quality of Life Questionnaire indicated these patients and their caregivers perceive an overall high quality of life.

Overall, test and questionnaire results were notably different between participants with MMA and participants with PA. The study demonstrates that pilot studies can detect instruments that may not be appropriate for individuals with language or motor deficits and that may not provide a broad range of scores reflecting disease severity. It also provides a rationale for focusing on discrete neuropsychological domains since some aspects of functioning were less affected than others and some were more closely related to disease severity. When global measures are used, overall scores may mask specific deficits. A pilot study like this one cannot ensure that scores will change over time in response to a specific treatment in a clinical trial. However, it can avert the selection of instruments that do not show associations with severity or biomedical parameters likely to be the target of a clinical trial. A pilot study can also identify when differences in diagnoses and baseline functioning need to be addressed prior to developing the analytical plan for the trial.