A variety of mouse models for Down syndrome (Trisomy 21) have been created to test hypotheses about the correlation of phenotypes to gene content and copy number. Ts1Rhr mice are trisomic for a region on mouse chromosome 16 that is homologous to 5.3 Mb of human chromosome 21. Ms1Rhr mice are monosomic for this region. Magnetic Resonance Imaging (MRI) has revealed characteristic volumetric changes in the brains of humans with Down syndrome such as reductions in the cerebellum, hippocampus, and brain stem, and increases in the ventricles and thalamus. We used MRI with region of interest analysis to measure the volume of the thalamus and hypothalamus in Ts1Rhr, Ms1Rhr, and euploid control mice (n = 10-11 per group). Ts1Rhr mice had a 6.6% reduction and Ms1Rhr mice had an 8.2% reduction in the volume of the thalamus. Ts1Rhr and Ms1Rhr hypothalamic volumes were equivalent to controls. Conflicting data in mouse models show a lack of clarity on causative roles of regions homologous to human chromosome 21 in phenotypes related to the thalamus and hypothalamus in Down syndrome.
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