Date of Award

December 2017

Degree Type


Degree Name

Master of Science (MS)




Natalie Russo


autism spectrum disorder, concordance, intellectual functioning, monozygotic twins

Subject Categories

Social and Behavioral Sciences


This study sought to examine the cognitive and neuropsychological performance of monozygotic twin pairs who vary in concordance for ASD. The study used secondary data collected from a larger pilot study, resulting in a final sample of 28 children, all of whom were monozygotic twins (IQ range: 36 – 109). First, the study sought to determine whether pairwise concordance for ASD among monozygotic twins has changed with the use of new diagnostic criteria. McNemar tests found that pairwise concordance rates were not significantly different across DSM-IV-TR and DSM-5 diagnostic criteria, but were significantly greater with the use of either parent report or direct observation as compared to both measures for DSM-5 criteria. Secondly, the study examined the relationship between IQ and ASD symptomatology using ordinal logistic regression, finding that a decrease in IQ did not predict greater severity of ASD symptoms as measured by the Calibrated Severity Score (Gotham, Pickles, & Lord, 2009), but did predict greater symptom severity as measured by the total algorithm score of the Autism Diagnostic Interview-Revised (Lord, Rutter, & Le Couteur, 1994). Third, the study examined IQ performance in relation to concordance, finding that the relationship between concordance and IQ was not significant for any area score. Finally, the study examined relative strengths and weaknesses of neuropsychological performance for children with ASD, with no significant differences in performance found for any of the NEPSY subtests examined (Korkman, Kirk, and Kemp, 1998). Results from this study support the idea that the phenotypic characteristics of autism spectrum disorder are heterogeneous even among children with the same genotype.


Open Access



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