Scientists have successfully turned off the chromosome defect that causes Down syndrome.
Down syndrome, also called Trisomy 21, is a genetic condition in which a person has three copies of chromosome 21, resulting in 47 chromosomes instead of 46. It is one of the most common causes of human birth defects. According to the Centers for Disease Control and Prevention, Down syndrome had an incidence rate of 11.8 babies per 10,000 live births from 1999 to 2003.
While gene therapy has been used to fix defective genes, this is the first time scientists were able to completely shut off an entire chromosome, they said.
Researchers found a way to copy the natural way the body turns off one of the two X chromosomes that all female mammals have. They found that both chromosomes have a gene they called “XIST” that when turned on, makes an RNA molecule that envelops a chromosome. This stops this chromosome from having its genes expressed. When the XIST is turned on in women, it quiets their other X chromosome.