SAN FRANCISCO—Early in his career, Daniel Kastner, MD, PhD, scientific director at the National Human Genome Research Institute, saw a 24-year-old patient with a lifelong history of recurrent fever and severe episodes of arthritis. A colleague told him it was most likely familial Mediterranean fever (FMF).
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There was little then known about its mechanisms, and a curiosity about the inner workings of the disease led him to a decades-long pursuit. The quest for knowledge about the single gene responsible for the disease, recounted by Dr. Kastner in his Paul Klemperer, MD, Memorial Lecture given at the 2015 ACR/ARHP Annual Meeting, has, many years later, resulted in a detailed model and is a lesson in scientific doggedness.
It’s one example, Dr. Kastner said, in a series of recent discoveries involving auto-inflammatory diseases in which patients have seemingly unprovoked episodes of inflammation without the usual high titer of autoantibodies or antigen-specific T cells seen in traditional autoimmune diseases.
“There’s really a lot of excitement still in the field,” Dr. Kastner said.
At the time he saw the 24-year-old patient, FMF was known to be caused by a single gene, but “nothing was known about the gene itself,” including its chromosomal location or its protein product, Dr. Kastner said. The Human Genome Project was just taking off, and Dr. Kastner considered it a well-timed “scientific opportunity.”
Meeting in 1989 in Israel, he and colleagues drew blood from FMF patients and their families. He then used those samples to study the DNA, eventually mapping the gene to the distal part of chromosome 16. His lab then further narrowed down the region, and, in 1997, discovered a novel gene that encodes a protein they called pyrin, after pyrexia for fever.
Then, Dr. Kastner said, they had to figure out what the gene did.
They found that the terminal end of the protein encoded a 90-amino-acid section—called the pyrin domain—that can form a cognate interaction, meaning it can interact with other pyrin domains in other proteins. They found that the pyrin domain of the pyrin protein interacts with the pyrin domain of the ASC protein. That protein has a domain called CARD, which interacts with the CARD domain of Caspase-1, the enzyme that activates pro-IL-1-beta into IL-1, a major mediator of fever and inflammation.
This finding gave clinicians a tool for distinguishing patients with FMF, and offered the opportunity to use IL-1 inhibitors in patients who didn’t respond to standard treatments—a therapeutic option that has been vital for many patients, Dr. Kastner said.
Many “inflammasome” molecules like pyrin are sensors for microbial infections—but researchers, at that point, still didn’t know the function of pyrin. A team of researchers in Beijing then reported that the pyrin inflammasome is activated by the toxins of certain bacteria—including Clostridium botulinum and Clostridium difficile—that interact with and inactivate Rho-GTP-ase (RhoA), binding proteins that regulate a wide variety of cell functions.
One of RhoA’s functions is to allow the organization of the cytoskeleton in white blood cells in response to an infection—exactly the kind of function bacteria would want to try to wipe out, Dr. Kastner said.
Over the past year, Dr. Kastner’s lab has delved into the mechanisms by which RhoA affects the activation of the pyrin inflammasome. Bit by bit, they built a mechanistic model.
They now believe that activating RhoA activates protein kinase N1 (PKN1), which phosphorylates pyrin. That leads to the binding of the 14-3-3 protein to pyrin, which acts as a kind of molecular switch to turn off the pyrin inflammasome.
His lab has since found that RhoA is also implicated in another periodic fever syndrome—hyperimmunoglobulinemia D with periodic fever syndrome (HIDS)—except that the process in that disease seems to be brought about by a mutation in the mevalonate kinase gene, Dr. Kastner said.
‘I predict that identification of somatic mutations in known fever genes will be there in at least 5% of adults with unexplained adult-onset recurrent fevers of more than a year’s duration.’ —Dr. Kastner
Research has proceeded in a flourish, with other auto-inflammatory diseases having recently been discovered, including NLRC4-macrophage activation syndrome; DADA2, or deficiency of adenosine deaminase type 2; and a dominantly inherited form of Behçet’s disease, with onset in childhood and characterized by mutations in the TNFAIP3 gene.
The next several years will continue to yield big discoveries in the auto-inflammatory diseases, using new genetic technologies, Dr. Kastner predicted.
In the next five years, he said, exome sequencing will become “available for whoever needs it.” Also, he said, “with big data, there will be more and more opportunities for comparing the sequences of the patients we see with sequences that other people see to put two and two together.”
He also predicted that the next five years will produce at least 50 new germline auto-inflammatory loci and at least 10 new auto-inflammatory pathways.
“I predict that identification of somatic mutations in known fever genes will be there in at least 5% of adults with unexplained adult-onset recurrent fevers of more than a year’s duration,” he said. “And I believe that in the next five years, someone will come up with an effective predictive model for at least one genetically complex auto-inflammatory disease.”
Thomas R. Collins is a medical writer based in Florida.
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