White-matter relaxation time and myelin water fraction differences in young adults with autism
Deoni SCL., Zinkstok JR., Daly E., Ecker C., Williams SCR., Murphy DGM., Bailey AJ., Baron-Cohen S., Bolton PF., Bullmore ET., Carrington S., Chakrabarti B., Daly EM., Deoni SC., Ecker C., Happe F., Henty J., Jezzard P., Johnston P., Jones DK., Lombardo M., Madden A., Mullins D., Murphy CM., Murphy DG., Pasco G., Sadek S., Spain D., Steward R., Suckling J., Wheelwright S., Williams SC.
Copyright © 2014 Cambridge University Press. Background. Increasing evidence suggests that autism is associated with abnormal white-matter (WM) anatomy and impaired brain 'connectivity'. While myelin plays a critical role in synchronized brain communication, its aetiological role in autistic symptoms has only been indirectly addressed by WM volumetric, relaxometry and diffusion tensor imaging studies. A potentially more specific measure of myelin content, termed myelin water fraction (MWF), could provide improved sensitivity to myelin alteration in autism. Method. We performed a cross-sectional imaging study that compared 14 individuals with autism and 14 age- and IQ-matched controls. T < inf > 1 < /inf > relaxation times (T < inf > 1 < /inf > ), T < inf > 2 < /inf > relaxation times (T < inf > 2 < /inf > ) and MWF values were compared between autistic subjects, diagnosed using the Autism Diagnostic Interview - Revised (ADI-R), with current symptoms assessed using the Autism Diagnostic Observation Schedule (ADOS) and typical healthy controls. Correlations between T < inf > 1 < /inf > , T < inf > 2 < /inf > and MWF values with clinical measures [ADI-R, ADOS, and the Autism Quotient (AQ)] were also assessed. Results. Individuals with autism showed widespread WM T < inf > 1 < /inf > and MWF differences compared to typical controls. Within autistic individuals, worse current social interaction skill as measured by the ADOS was related to reduced MWF although not T < inf > 1 < /inf > . No significant differences or correlations with symptoms were observed with respect to T < inf > 2 < /inf > . Conclusions. Autistic individuals have significantly lower global MWF and higher T < inf > 1 < /inf > , suggesting widespread alteration in tissue microstructure and biochemistry. Areas of difference, including thalamic projections, cerebellum and cingulum, have previously been implicated in the disorder; however, this is the first study to specifically indicate myelin alteration in these regions.