The assessment and diagnosis of intellectual disability when development is atypical. A Norwegian population study of individuals with CHARGE syndrome

Lynn Skei; Sigmund Skei; Stephen von Tetzchner; Timothy Hartshorne; Nils Inge Landrø

doi:10.1080/00207454.2023.2240485

The assessment and diagnosis of intellectual disability when development is atypical. A Norwegian population study of individuals with CHARGE syndrome

Int J Neurosci. 2023 Sep 7:1-14. doi: 10.1080/00207454.2023.2240485. Online ahead of print.

Authors

Lynn Skei^{1

2}, Sigmund Skei³, Stephen von Tetzchner¹, Timothy Hartshorne⁴, Nils Inge Landrø¹

Affiliations

¹ Department of Psychology, University of Oslo, Oslo, Norway.
² Signo Resource Centre, Sandefjord, Norway.
³ County Governor Vestfold & Telemark, Vestfold, Norway.
⁴ Department of Psychology, Central MI University, Michigan.

PMID: 37675478
DOI: 10.1080/00207454.2023.2240485

Abstract

Aim: This paper aimed to answer how psychometric methods based on neurotypical populations can serve as valid instruments in the assessment and diagnosis of intellectual disability in individuals with atypical development. The genetic, structural, and functional features of CHARGE make it uniquely suited to address this question.

Method: A Norwegian population of individuals with CHARGE (N = 35) underwent assessment procedures according to DSM-5 guidelines for the evaluation of an intellectual disability diagnosis. Results from cognitive testing (Wechsler Intelligence Scales) and parental evaluation of adaptive skills (Vineland Adaptive Behavioral Scale) were obtained and compared to their respective norm samples to explore any methodological inconsistencies.

Result: Significant differences emerged between the participants and the norm samples. Global cognition obtained from Wechsler revealed a bimodal distribution, suggesting a two-group sample, with the youngest children forming their own subgroup. Comparisons of the different age-groups' performances demonstrated the lowest results among the preschoolers while the adults scored the highest. The global adaptive behavior score turned out significantly lower than the performance-based scores, thereby deflating the overall estimate of global intellectual abilities.

Conclusion: For individuals with CHARGE, the effect of the atypicality seemed most apparent during early childhood, stabilizing and subsiding towards adulthood. The test results' interpretability was weakest for the preschoolers progressively increasing until peaking in adulthood, emphasizing the importance of delaying the assessment and diagnosis of intellectual disability. Because of several validity issues connected to the observation-based measure, complementary testing should precede clinical evaluations when possible in the diagnostics of individuals with CHARGE.

Keywords: Assessment and diagnosis of intellectual disability; CHARGE syndrome; atypical development; norm-referenced assessment; population study.