In this same sense, XIST has been used to perform chromosomal silencing studies on chromosome 21 (Down syndrome), and it was found that overexpression of XIST leads not only to inactivation of the extra chromosome but also to a defined effect on the expression profile genomics that triggers stable heterochromatin modifications, chromosome‐wide transcriptional silencing, and DNA methylation to form a “chromosome 21 Barr body.” This initiates effects on heterochromatin, regulates transcription, and induces some biochemical variations such as DNA methylation. This evidence concerns the gene XIST and Down syndrome.