Convergent Validity of the Fine Motor, Speech, and Cognitive Domains of the 5-Domain Niemann-Pick Disease Type C Clinical Severity Scale

The 5-Domain Niemann Pick Type C Clinical Severity Scale (5DNPCCSS) is used in clinical practice and trials. Although psychometric data support the clinical meaningfulness of the concepts and the scale's interrater reliability, more information is needed to support its construct validity. Here, we evaluated the convergent validity of the Cognition, Speech, and Fine Motor domains. Data from 121 individuals with Niemann-Pick disease type C were drawn from several studies conducted at 2 US sites. Direct standardized assessments included the Nine-Hole pegboard or Purdue pegboard, a portion of the Clinical Evaluation of Language Fundamentals, and the age-appropriate Wechsler IQ test or the Mullen Scales of Early Learning. The 5DNPCCSS domains were significantly related in the expected directions to their respective direct assessments, supporting their construct validity. In combination with previous evidence presented for the Ambulation and Swallow domains, these results support the fitness of purpose of the (5DNPCCSS for clinical studies in Niemann-Pick disease type C. ClinicalTrials.gov: NCT00344331, NCT01747135, NCT02534844.