Vexas would have been discovered a long time ago if it were a garden variety genetic disease, caused by an inherited genetic mutation. For instance, the single gene responsible for familial Mediterranean fever, also an inflammatory disease, was identified in 1997 by screening the DNA of families that carried the disease. But Vexas can’t run in families. Like cancer, Vexas is caused by what scientists call a “somatic mutation,” a gene mutation that develops in someone’s body after they are born.
Because somatic mutations appear later in life, they affect only a fraction of a person’s cells, which makes them difficult to find. Conventional genetic analyses will miss them entirely:
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