Researchers find cause of new autoinflammatory disease
By Prabarna Ganguly, Ph.D.
Members of three families came to NIH’s Clinical Center with symptoms similar to those caused by an autoinflammatory disease, but with no known cause. The seven patients ranged from 10 to 82 years old. Their symptoms included fevers, swollen lymph nodes, severe abdominal pain, gastrointestinal problems, headaches and, in some cases, abnormally enlarged spleen and liver. Although their condition isn’t life-threatening, they can have persistent fever and swollen lymph nodes from childhood to old age, as well as other symptoms that can lead to lifelong pain and disability.
A team of researchers led by Dr. Daniel Kastner of NIH’s National Human Genome Research Institute (NHGRI) and Dr. John Silke at the Walter and Eliza Hall Institute in Australia carried out a study looking for the cause of the syndrome. After ruling out infections and cancer, they sought answers by genomic sequencing. The study, which was funded by several NIH components, was published on January 2, 2020, in Nature.
The team discovered only one gene—RIPK1—that was consistently different in all patients. Each of the three families had its own unique mutation affecting the very same DNA letter in the RIPK1 gene. Each affected person had one mutant and one normal copy of the gene, while unaffected family members had two normal copies.
The protein encoded by the RIPK1 gene is involved in inflammation and programmed cell death—the process by which old cells die so they can be replaced by new ones. Each of the patients’ mutations occur at the location where RIPK1 can be cleaved to prevent it from initiating inflammation and cell death. Thus, Kastner’s team named the disease cleavage-resistant RIPK1-induced autoinflammatory, or CRIA, syndrome.
Mouse embryos with two mutant copies of RIPK1 did not survive in the uterus due to excessive cell death signals. However, mice with one mutant copy and one normal copy, like the CRIA patients, were mostly normal but had heightened inflammatory responses.
The team tested therapies known to reduce inflammation in seven patients with CRIA syndrome. While drugs such as etanercept and anakinra, which are used to treat autoinflammatory and chronic diseases such as rheumatoid arthritis, had little effect, one drug called tocilizumab did. Tocilizumab is a drug that suppresses a specific signaling molecule in the immune system. It reduced the severity and frequency of CRIA syndrome symptoms in five out of the seven patients—in some cases with life-changing effects.
“This discovery underscores the tremendous power of combining astute clinical observation, state-of-the-art DNA sequencing, and the sharing of sequence data in large publicly-accessible databases,” Kastner says.
Researchers are now trying to understand the molecular mechanism that enables tocilizumab to treat CRIA syndrome. Specific inhibitors of RIPK1, which are under development, may also hold promise in both CRIA syndrome and other seemingly intractable inflammatory conditions.