A strange study on lab mice indicates that giving bone marrow transplants might not just change a person's immune system, it might even change the way they act. Take a look at the mouse study and see what you think.
In humans, it's called trichotillomania. Certain people feel a compulsion to pull out their hair, their eyebrows, or their eyelashes. They can have a mild form of the disorder, or they can learn to mask it by picking hair from spots that most people don't see, but it almost always results in bald patches.
Humans are not the only ones to have this disorder. A number of other mammals pull out their hair, or the hair of their companions. (Young children with trichotillomania also pull out other people's hair, but they stop as they get older.) Mice who do this are called barbers. They will pull out specific patches of their own hair or whiskers, and will sometimes pull the hair and whiskers out of the mice around them. Their companions can accept this quite placidly, and sometimes even go up to the barber to be plucked.
Because it has only been observed in captive populations, people considered it a disorder brought on by stress or boredom. Although stress still might precipitate the behavior, one study indicates that the source of trichotillomania could be physical, not mental. A group of mutant mice, missing the Hoxb8 gene, grew up to be extreme barbers. When they ran out of hair, they would scratch at their skin until they had sores, but in other ways, they were normal mice.
The Hoxb8 gene is part of a group of 39 genes. The Hox genes regulate functions as diverse as embryonic development, hair development in adults, and breast tissue development. Hoxb8 helps develop the macrophages — cells that eat viruses, bacteria, and other foreign objects inside the body — that are specifically found in the brain. These macrophages, called microglia, are one of the elements of the immune system made by bone marrow. The mutant Hoxb8-deprived mice got bone marrow transplants from regular mice. A month later, the mice stopped self-barbering. Three months later, they were normal, hairy mice.
We've seen that a bone marrow transplant can have odd, lasting effects. It can, for example, change a person's blood type . This study indicates that it can also change a person's behavior by changing the ecology of their brain.
There are a number of leaps to be made between mice and humans. We have to see if people with trichotillomania also have defective Hoxb8 genes — or analogous problem genes. And it's certainly possible that a treatment that works on mice doesn't work on humans. Still, it's an interesting idea. We might be at least capable of manipulating how a human being acts by manipulating their bone marrow.
Top Image: Rama.