White-matter relaxation time and myelin water fraction differences in young adults with autism

<jats:sec id="S0033291714001858_sec_a1"><jats:title>Background</jats:title><jats:p>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 <jats:italic>indirectly</jats:italic> 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.</jats:p></jats:sec><jats:sec id="S0033291714001858_sec_a2" sec-type="methods"><jats:title>Method</jats:title><jats:p>We performed a cross-sectional imaging study that compared 14 individuals with autism and 14 age- and IQ-matched controls. <jats:italic>T</jats:italic><jats:sub>1</jats:sub> relaxation times (<jats:italic>T</jats:italic><jats:sub>1</jats:sub>), <jats:italic>T</jats:italic><jats:sub>2</jats:sub> relaxation times (<jats:italic>T</jats:italic><jats:sub>2</jats:sub>) 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 <jats:italic>T</jats:italic><jats:sub>1</jats:sub>, <jats:italic>T</jats:italic><jats:sub>2</jats:sub> and MWF values with clinical measures [ADI-R, ADOS, and the Autism Quotient (AQ)] were also assessed.</jats:p></jats:sec><jats:sec id="S0033291714001858_sec_a3" sec-type="results"><jats:title>Results</jats:title><jats:p>Individuals with autism showed widespread WM <jats:italic>T</jats:italic><jats:sub>1</jats:sub> 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 <jats:italic>T</jats:italic><jats:sub>1</jats:sub>. No significant differences or correlations with symptoms were observed with respect to <jats:italic>T</jats:italic><jats:sub>2</jats:sub>.</jats:p></jats:sec><jats:sec id="S0033291714001858_sec_a4" sec-type="conclusion"><jats:title>Conclusions</jats:title><jats:p>Autistic individuals have significantly lower global MWF and higher <jats:italic>T</jats:italic><jats:sub>1</jats:sub>, 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.</jats:p></jats:sec>