Gene therapy for Down syndrome.

The presence of an additional copy of HSA21 chromosome in Down syndrome (DS) individuals leads to the overexpression of 30-50% of HSA21 genes. This upregulation can, in turn, trigger a deregulation on the expression of non-HSA21 genes. Moreover, the overdose of HSA21 microRNAs (miRNAs) may result in the downregulation of its target genes. Additional complexity can also arise from epigenetic changes modulating gene expression. Thus, a myriad of transcriptional and posttranscriptional alterations participate to produce abnormal phenotypes in almost all tissues and organs of DS individuals. The study of the physiological roles of genes dysregulated in DS, as well as their characterization in murine models with gene(s) dosage imbalance, pointed out several genes, and functional noncoding elements to be particularly critical in the etiology of DS. Recent findings indicate that gene therapy strategies-based on the introduction of genetic elements by means of delivery vectors-toward the correction of phenotypic abnormalities in DS are also very promising tool to identify HSA21 and non-HSA21 gene candidates, contributing to DS phenotype. In this chapter, we focus on the impact of normalizing the expression levels of up or downregulated genes to rescue particular phenotypes of DS. Attempts toward gene-based treatment approaches in mouse models will be discussed as new opportunities to ameliorate DS alterations.