Concordance in Inhibitory Event Related Potentials Among Twins with and without Autism

Background: Concordance rates among twins provide evidence that genetic factors contribute to risk for autism spectrum disorder (ASD). Twin studies may also be informative about potential endophenotyes in ASD. One potential endophenotype, response inhibition, is a core executive function. Inhibition is related to cognitive flexibility, which is impaired in autism (Russo et al 2007). Anokhin et al (2004) identified heritability estimates for the inhibitory paradigm (Go/No-Go) event-related potential (ERP) responses N2 and P3 at 60% and 41%, respectively, in an adult non-affected twin sample. However, heritability in twins with ASD has not been examined. The current study uses neurophysiological measurement (ERP) to explore the correlation between N2 and P3 responses in twins with ASD and typical development (TD). The N2 and P3 are related to monitoring and inhibition, respectively.

Objectives: This study examined correspondence within monozygotic (MZ) twin pairs relative to dizygotic (DZ) twin pairs during a Go/No-Go task for the N2 and P3 ERP components. Stronger correspondence within MZ twin pairs relative to DZ pairs would provide support for genetic contributions to this domain. 

Methods: The sample included 12 MZ and 6 DZ twin pairs with typical development and 8 MZ and 6 DZ twin pairs with ASD. Twins ranged in age from 7 years to 22 years (mean = 12.1 years). Electrophysiological responses were continuously recorded with high-density EEG as twins completed a Go/No-Go task with shapes. The average mean amplitude for the N2 at Fz and P3 at Pz was obtained for each twin in the Go and No-Go conditions. 

Results: Among MZ twins with TD, a significant relation was detected in the N2 Go condition, r(12) = .69, p = .01 and no relations were detected among DZ twins with TD. Among MZ twins with ASD, a trend was detected in the N2 Go condition, r(11) = .87, p = .06. In addition, the DZ group with ASD had significant relations in the N2 Go condition, r(6) = .84, p = .04 and the P3 Go condition, r(6) = .82, p < .05.  

Conclusions: These results suggest that the N2 ERP response was more related within MZ than DZ twins with typical development. This is consistent with a stronger genetic contribution for task monitoring during the Go/No-Go task among typically developing twins. In contrast, among the twins with ASD the N2 ERP in Go condition was related within both MZ and DZ twin pairs. This suggests a stronger environmental contribution to performance among twins with ASD. Additional support for environmental influences on performance among the twin pairs with ASD was observed at the P3 component, which was more related in DZ twins. These results are intriguing as they are suggestive of a different pattern of factors that contribute to task monitoring and response preparation in twins with ASD as compared with TD. However, the sample size of this exploratory study is small, and replication will be essential.