A small segment of the population is literally allergic to vibrations, an annoying condition that gives rise to hives and other symptoms. Researchers at the NIH have now isolated the genetic mutation responsible for the disorder, and it's offering new insight into related conditions. This type of allergy is called a physical urticaria, and it typically produces hives after exposure to heat, cold, water, sunlight, sweat and exercise. But for a select group of people, this exaggerated autoimmune response is triggered by vibrations -- things like running, towel drying, hand clapping and even motorcycle rides can all cause symptoms. The new NIH study, which now appears in the New England Journal of Medicine, suggests that people with this rare form of urticaria are prone to an out-of-whack cellular response when their skin touches something that vibrates. This response causes their immune system to release inflammatory chemicals that produce hives and other allergic symptoms.
In addition to the itchy red welts at the site of the vibration, people with this form of urticaria experience flushing, headaches, fatigue, blurry vision and sometimes a metallic taste in the mouth. Thankfully, these symptoms don't tend to last long, and they disappear within a few hours.
To give you a sense of how rare this condition is, the NIH researchers had only three multi-generational families to work with. Analysis of their DNA, including those of unaffected family members, pointed to a mutation in the ADGRE2 gene. At the same time, the researchers didn't detect the mutation in databases or in the DNA of more than 1000 unaffected individuals with similar genetic ancestry.
This particular gene provides instructions for a protein that's present on the surface of certain immune cells, including mast cells (a type of white blood cell). These cells reside in the skin and other tissues, and release histamine and other inflammatory chemicals into the bloodstream and nearby tissue in response to certain stimuli. In the case of this urticaria, that stimuli is vibration. Tests showed that individuals with this form of urticaria experience a significant increase in blood histamine levels and a major release of tryptase (another trigger of mast cell activity) in the presence of vibrations. The same could not be said for unaffected individuals.
What's more, the researchers learned the protein encoded by ADGRE2 produces two subunits -- one on the cell's outer membrane and one on the outside surface of the cell -- that normally interact and stay close together. But people with vibratory urticaria make mutated ADGRE2 proteins in which these subunits are less stable, leading to "degranulation", which causes hives and other symptoms.
"This work marks, to the best of our knowledge, the first identification of a genetic basis for a mast-cell-mediated urticaria induced by a mechanical stimulus," noted study co-author Dean Metcalfe in a press statement.
This research means that ADGRE2 is probably responsible for other diseases in which mast cells are involved. Looking ahead, the NIH researchers want to study what happens at the cellular level immediately after exposure to vibrations. They're also hoping to study more families with this rare allergic disorder.
This is all enlightening research, but unfortunately for people who suffer from the condition, a treatment isn't on the drawing board. In the future, presumably some gene therapy could shake up the disorder and rid people of this annoying allergy.
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