In order to identify early risk markers for autism spectrum disorder (ASD), investigators at University of California Davis School of Medicine and Davis Children’s Hospital conducted a longitudinal brain MRI study of infant siblings in conjunction with behavioral assessments leading to an outcome classification at 24 months or later (mean age 32.5 months). Fifty-five infants (33 ‘high-risk’ infants having an older sibling with ASD and 22 ‘low-risk’ infants having no relatives with ASD) were imaged at three time points: 6-9 months, 12-15 months, and 18-24 months of age. Compared to infants classified as developmental delay or typical development, 10 infants who developed ASD had significantly greater extra-axial fluid at 6-9 months, which remained elevated at 12-15 and 18-24 months. The amount of extra-axial fluid detected at 6 months was predictive of more severe ASD symptoms at time of outcome. Infants who developed ASD also had significantly larger total cerebral volumes at both 12-15 and 18-24 months of age. These novel findings raise the potential for use of structural MRI to aid in early detection (6-9 months of age) of children at risk for ASD. 
COMMENT. The clinical diagnosis of ASD is usually delayed until at least 18 months of age. This study provides a potential brain MRI biomarker for the earlier diagnosis and treatment of ASD in at risk infants.
Extra-axial fluid accumulation (communicating hydrocephalus) with rapid head growth in the first year of life typically resolves without intervention, but it may be associated with seizures and motor delays  and now is associated with development of ASD. Extra-axial fluid and rapid head growth in infancy is not always a benign reversible disorder.
Neurobiological abnormalities in infants who later develop ASD
Studies since 2009 showing abnormalities in head circumference, electrophysiological markers and interhemispheric synchronization and differences in various brain regions (amygdala, cerebellum, frontal and temporal cortex) are reviewed by investigators at the University of Glasgow, Scotland. Cross-disciplinary approaches are essential to elucidate sequence of developmental abnormalities during early infancy leading to ASD. 
Eyeblink conditioning (EBC) is proposed as a non-invasive biomarker for ASD that can be employed shortly after birth . The neural circuitry for EBC involves sensory information from the cornea to the trigeminal nucleus, the interpositus nucleus and cerebellar cortex.