The researchers discovered that the number of alopecia-associated genes a person had correlated with the severity of the condition. Those who carried 16 or more genes (the genes are in pairs) were more likely to progress to alopecia universalis, or total hair loss.
Researchers had expected that alopecia genes would be the same as those associated with other autoimmune diseases of the skin, such as psoriasis (in which the immune system signals the overproduction of skin cells, resulting in dry, scaly lesions) or vitiligo (loss of pigment to the skin when cells called melanocytes no longer function).
Yet alopecia and psoriasis had only one of the eight genes in common, Christiano said.
"We undertook this genome-wide association study to ask in an unbiased way, and to let the genes tell us, what are the likely associations with alopecia areata," Christiano said. "We were very surprised to find the genes that came up have a mechanism shared by type I diabetes and rheumatoid arthritis."
In people with alopecia, immune system T cells are present in large numbers in the hair follicle. Under a microscope, "it looks like the hair follicle is being swarmed or attacked by bees, which are the T cells," she explained.
What researchers didn't know was what attracted the "bees" in the first place, though the study hints at the answer.
Among the eight genes, one in particular -- ULBP3 -- has been shown to attract toxic cells that can invade and destroy an organ. In a person without alopecia, ULBP3 is turned off. But in people with alopecia, ULBP3 proteins are plentiful in the follicle.
"In people with alopecia areata, we see a huge expression of the ULBP3 gene in the outermost layer of the follicle," Christiano said. "ULBP3 is a danger signal that signals to T cells to come in and attack the follicle. It's like putting nectar on the hair follicle, then the 'bees' come in and do their damage."
When the follicle is attack
All rights reserved