There are over 1,000 X-linked genes, including the genes for red-green color blindness, hemophilia, male pattern baldness, and body fat distribution. And if you remember your high school genetics, males have one “X” and one “Y” chromosome, and females have two “X” chromosomes.
Since females have two “X” chromosomes, only one of the X chromosomes will be expressed in any given cell. The determination of which one is expressed is random. Tortoiseshell and calico cats (all females) are the perfect example- they have a gene for orange fur on one of their X chromosomes, and a gene for black fur on the other. Their random coat patterns are due to the random expression of X-chromosomes; areas where the fur is black express the X-chromosome with the black fur gene, and areas where the fur is orange express the X-chromosome with the orange fur gene.
OK, so the cats look pretty awesome. But it doesn’t stop there. Researchers are working with calico cats to try to understand how X-chromosomes are inactivated, in an attempt to figure out a way to turn certain genes on or off in a way that isn’t random. How cool would it be if genes linked to obesity or other diseases could be selectively silenced without altering a person’s DNA? Or if X-chromosome linked disorders could be silenced in a way that they wouldn’t be passed down to our offspring?
Millions of people around the world suffer from hemophilia, a bleeding disorder that prevents the blood from clotting properly. Often, diseases that are found in humans are also found in animals, and in this study, researchers worked to find a treatment for dogs with naturally occurring hemophilia A.
Patients that suffer from hemophilia lack a coagulation factor (factor VIII) in their blood plasma. One treatment is to replace factor VIII via injection, but many hemophiliacs don’t respond to factor VIII therapy.
So researchers at the Medical College of Wisconsin figured out a way to ‘sneak’ factor VIII into the body. They took cells that would eventually turn into platelets and engineered them to express factor VIII. The cells were put into the dogs and began to make platelets. And when bleeding events started, these platelets did their jobs and dumped their contents at the bleeding site- sending factor VIII right where it was needed!
Before this gene therapy, these Great Pyrenees had approximately five serious bleeding events each year. But after introducing these engineered platelet precursor cells, that number was significantly reduced, and the bleeding events were easily treatable! And 2 1/2 years after the gene therapy, platelets are still expressing factor VIII.
Next step: human clinical trials. Is this an example of humans helping animals… or animals helping humans?