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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.

Background Multiple Sclerosis is characterized by neural demyelination. Structural magnetic resonance imaging (MRI) provides soft tissue contrast, which forms the basis of techniques for extracting regional biomarkers across a participant's brain. Objectives To investigate the clinical presentation of multiple sclerosis in a large‐scale MRI analysis that includes thorough consideration of extractable structural measurements (average and variability of regional cortical thicknesses, cortical surface measurements, and volumes). Methods We performed a large‐scale retrospective analysis of 370 T1 structural volumetric MRIs from 64 participants with multiple sclerosis and compared them with a large cohort of neurotypical participants, consisting of 993 MRIs from 988 participants. Regionally distributed measurements of cortical thickness (average and standard deviation) were extracted along with surface area, surface curvature, and volumetric measurements. Results The largest observed finding involved regionally distributed reductions in average cortical thickness, with the parahippocampal region exhibiting the largest effect size, a finding that may be linked with known hippocampal atrophy in multiple sclerosis. Group‐wise differences were also observed in terms of distributed volume, surface area, and surface curvature measurements. Conclusions Participants with pediatric‐onset multiple sclerosis present clinically with a variety of structural abnormalities, including perirhinal cortex thickness abnormalities not previously reported in the literature.

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