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= Mouse Models of Down Syndrome = Mouse model s have frequently been used to study Down syndrome due to the close similarity in the genomes of mice and humans, and the prevalence of mice usage in laboratory research.

Background
Trisomy 21, an extra copy of the 21st chromosome, is responsible for causing Down syndrome, and the mouse chromosome 16 closely resembles human chromosome 21. In 1979, trisomy of the mouse chromosome 16 (Ts16) initially showed potential to be a model organism for human Down syndrome. However, Ts16 embryos rarely survive until birth, making them unable to serve as a model for behavior and postnatal development. This dissimilarity in survival between species arises from the presence of genes on mouse chromosome 16 that are not present on human chromosome 21, introducing additional gene dosage imbalances. Because of this disadvantage, more specific mouse models have been utilized.

Model
The Ts65Dn mouse model was first introduced in 1993 and more specifically resembles human trisomy 21 than the Ts16 model. In Ts65Dn, cells possess an extra copy of a segment of genes on chromosome 16 as well as a segment of genes on chromosome 17. From this model, various Down syndrome phenotypes are produced, including behavioral abnormalities and cognitive defects.

Findings
This model was studied to understand the neurological basis of its mental impairment. It was found that it exhibited inhibition in the dentate gyrus, and that GABAA antagonists were able to resolve some of this impairment. These mice were found to experience a delay in development, exhibit unusual behaviors similar to human retardation, and eventually encounter astrocytic hypertrophy and other forms of neurodegeneration. They also contained abnormally large neural synapses and other structural changes.

Model
The Dp(16)1Yu model (also referred to as Dp(16)1Yey) contains a partial duplication of the mouse chromosome 16. Unlike the Ts65Dn model, Dp(16)1Yu contains a duplication of only the parts of chromosome 16 that are homologous to human chromosome 21. This makes the Dp(16)1Yu model a more genetically accurate representation of Down Syndrome. This model presents an array of symptoms, including an increased rate of heart defects and learning and memory deficits which are comparable to symptoms seen in Down Syndrome. These mice also show an increased rate of birth defects in the pancreas (see annuler pancreas) and intestinal malrotation.

Findings

 * 1) Pharmacotherapy for cognitive impairment in a mouse model of Down syndrome.
 * 2) Developmental abnormalities and age-related neurodegeneration in a mouse model of Down syndrome.
 * 3) Synaptic structural abnormalities in the Ts65Dn mouse model of down syndrome.