<prompt> In autism spectrum disorder, which of the following is identified as the first biomarker ?Decreased brain volume in children less than 4 yearsReduced latency of sleepIncreased level of serotonin in the plateletsIncreased levels of dopamine  <response>: In autism spectrum disorder, level of serotonin in the platelets is identified as the first biomarker. Other biomarkers are mTOR pathway Increased total brain volume in children 4 years of age g-aminobutyric acid GABA inhibitory system 