White Matter Microstructure of Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD)

Background: Previous researches have shown high rate of comorbidity (30-50%) between attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Several studies reported that impaired structural brain connectivity was related to the core features of ASD and ADHD. However, only a few studies directly compared the white matter microstructure between ASD and ADHD. Sensory hypersensitivity is often existed in both individuals with ASD and those with ADHD, however little is known about the brain substrates related to sensory sensitivity in the two neurodevelopmental disabilities.

Objectives: The aim of the present study is to reveal the commonality and difference of white matter microstructure between adults with ASD and those with ADHD, especially concerning sensory sensitivity, using Diffusion Tenor Imaging (DTI).

Methods: A total of 218 adults participated in this study; 58 Normal Controls (NC), 105 ASD, 55 ADHD. Two medical specialists diagnosed ASD and ADHD according to DSM-5 criteria. ADOS-2 was conducted on 83 out of 105 ASDs. DTI data were processed using programs in the FMRIB Software Library (FSL) version 5.0. Automatic quality control was conducted with DTIprep. TOPUP was performed to correct susceptibility induced distortions. TBSS was used for voxelwise statistical analysis. Simple regression analysis using individual scores for sensory hypersensitivity was applied to FA values within clusters showing significant main effect of diagnosis on FA. The statistical threshold was defined at p < 0.05 (corrected for multiple comparisons). Age, gender and head motion were included as covariates.

Results: FA values of 7 clusters differed in FA across diagnostic groups. These clusters were located at genu, body, and splenium corpus callosum (CC) and posterior cocona radiata in right hemisphere. Post hoc analyses revealed both ASD and ADHD had lower FA compared to TD in 5 clusters. Two small clusters at genu of CC, voxel size 5 and 3, indicated reduced FA in ADHD compared to ASD and TD. Significant interaction effects of FA and sensory sensitivity were identified between Developmental Disabilities (DD) and NC in the cluster located at body of CC in right hemisphere.

Conclusions: Altered white matter microstructures in CC and posterior corona radiata were observed in both ASD and ADHD. Different effect of sensory hypersensitivity on FA was identified in CC between developmental disabilities and NC. This study suggested the similar alternation of white matter microstructure, including regarding sensory hypersensitivity, between ASD and ADHD. However, further studies are required to investigate the disorder-specific alternations since group differences in FA were observed between the two DDs in small regions.