Objective: To gain insight into the pathophysiology of an unusual autoinflammatory syndrome, in a patient of Armenian origin, that mimicked familial Mediterranean fever (FMF) but with episodes triggered by generalized exposure to cold, and to further elucidate the controversial function of the protein encoded by PYPAF1, whose mutations (exclusively missense to date) have been identified in 3 hereditary recurrent fever syndromes.
Methods: The patient's DNA was screened for mutations in both MEFV, the gene responsible for FMF, and PYPAF1. The ability of different recombinant PYPAF1 isoforms, expressed in HEK 293 cells, to regulate NF-kappaB signaling was subsequently assessed.
Results: No disease-causing mutation was found in MEFV. However, a nonsense mutation (p.Arg554X) was identified in PYPAF1; this defect resulted in a truncated protein lacking all leucine-rich repeats. Study of the wild-type and mutant PYPAF1 recombinant proteins revealed that PYPAF1 inhibited NF-kappaB proinflammatory pathways, and that the identified nonsense mutation impaired this property.
Conclusion: These molecular and clinical findings, together with the clinical manifestations in the patient, which call into question the current nosology of the hereditary recurrent fever syndromes, are consistent with the hypothesis that PYPAF1 acts as an inhibitor of NF-kappaB signaling. They also provide a clear elucidation of the functional consequences of this nonsense PYPAF1 mutation not previously described in the literature, which result in a partial loss of function and may thereby explain the pathophysiology of the autoinflammatory syndrome observed in this patient.