Autism is a group of complex neurodevelopmental disorders characterized by impaired social interaction, restricted and repetitive behavior. We performed a large-scale retrospective analysis of 1,996 structural magnetic resonance imaging (MRI) examinations of the brain from 1,769 autistic and neurologically typically developing patients (aged 0-32 years), and extracted regional volumetric measurements distributed across 463 brain regions of each patient. The youngest autistic patients (<2.5 years) were diagnosed after imaging and identified retrospectively. Our study demonstrates corpus callosum volumetric abnormalities among autistic patients that are associated with brain overgrowth in early childhood (0-5 years old), followed by a shift towards known decreased volumes in later ages. Results confirm known increases in ventricular volumes among autistic populations and extends those findings to increased volumes of the choroid plexus. Our study also demonstrates distributed volumetric abnormalities among autistic patients that affect a variety of key regional white and grey matter areas of the brain potentially associated with known symptoms of autism.

Autism is a group of complex neurodevelopmental disorders characterized by impaired social interaction and restricted/repetitive behavior. We performed a large-scale retrospective analysis of 1,996 clinical neurological structural magnetic resonance imaging (MRI) examinations of 781 autistic and 988 control subjects (aged 0–32 years), and extracted regionally distributed cortical thickness measurements, including average measurements as well as standard deviations which supports the assessment of intra-regional cortical thickness variability. The youngest autistic participants (<2.5 years) were diagnosed after imaging and were identified retrospectively. The largest effect sizes and the most common findings not previously published in the scientific literature involve abnormal intra-regional variability in cortical thickness affecting many (but not all) regions of the autistic brain, suggesting irregular gray matter development in autism that can be detected with MRI. Atypical developmental patterns have been detected as early as 0 years old in individuals who would later be diagnosed with autism.

Down syndrome (DS) is a genetic disorder caused by an extra copy of all or part of chromosome 21 and is characterized by intellectual disability. We performed a retrospective analysis of 47 magnetic resonance imaging (MRI) examinations of participants with DS (aged 5 to 22 years) and compared them with a large cohort of 854 brain MRIs obtained from neurotypical participants (aged 5 to 32 years) with the objective of assessing the clinical presentation of Down syndrome, towards better understanding the neurological development associated with the condition. An additional cohort of 26 MRI exams from patients with DS and 139 exams from neurotypical participants (aged 0–5 years) are included as part of a supplementary analysis. Regionally distributed cortical thickness measurements, including average measurements as well as standard deviations (intra-regional cortical thickness variability) were extracted from each examination. The largest effect sizes observed were associated with increased average cortical thickness in the postcentral gyrus with specific abnormalities observed in Brodmann's areas 1 and 3b in DS, which was observed across all age ranges. We also observed strong effect sizes associated with decreased cortical thickness variability in the lateral orbitofrontal gyrus, the postcentral gyrus and more in DS participants. Findings suggest regionally irregular gray matter development in DS that can be detected with MRI.