University of Washington researchers have done something seemingly impossible: they have removed the extra copy of chromosome 21 in cells taken from a patient with Down syndrome. This gene therapy technique targets only the extra genetic material in the cell, and scientists were able to successfully remove the extra chromosome 21 without damaging the integrity of the rest of the chromosomes present in the nucleus.
The first reaction to this news is to shout, “there’s a cure for Down Syndrome!” Unfortunately that is not the case. However, it might be a way to treat Down Syndrome patients who have blood cancers. Down syndrome patients are at increased risk for leukemia, and this technique, pioneered by Dr. David Russell and his colleagues is meant to fix the errant bone marrow cells in culture and then reintroduce the fixed cells back into the patient.
Dr. Russell explained: “We are certainly not proposing that the method we describe would lead to a treatment for Down syndrome. What we are looking at is the possibility that medical scientists could create cell therapies for some of the blood-forming disorders that accompany Down syndrome.” Dr. Russell is from the University of Washington’s Department of Medicine.
This technique works on cultured cells grown in a laboratory. The cells are infected with an engineered virus that inserts into the extra chromosome. Then the cells are grown under conditions that kill all cells with the viral DNA. Only those cells that spontaneously lose the extra copy of chromosome 21 survive the culture conditions.
This protocol could potentially treat Down syndrome patients with leukemia with genetically-modified stem cells that are derived from their own cells, but lack the extra chromosome. Stem cells could be taken from the bone marrow of the patients, the doctors could remove the extra chromosome, and then the healthy cells could then be grown and transplanted back into the bone marrow of the patient. This same technique could also be used for leukemia patients whose bone marrow cells have an extra chromosome, but do not have Down syndrome.
This is great news for those with Down syndrome and for all those who live with any kind of trisomy. Also, since gene therapy can introduce new defects into the patient’s DNA, this technique could potentially remove unwanted extra bits of DNA without adversely affecting other chromosomes. This is certainly a major achievement.