Objectives: Familial Mediterranean fever (FMF) is caused by mutations in MEFV, which encodes pyrin. The nature of substitutions P369S and R408Q in exon 3 remains unclear. Exon 3 encoding pyrin’s B-box domain is necessary for interactions with PSTPIP1. We aimed to characterize the phenotype of patients with these substitutions and to determine their functional significance.
Methods: A database of genetic tests undertaken in our institution was interrogated. Symptoms and signs were classified according to Tel-Hashomer criteria. Co-immunoprecipation techniques were employed to determine the variants’ effects on pyrin/PSTPIP1 interactions.
Results: We identified 40 symptomatic and 4 asymptomatic family members with these substitutions. P369S and R408Q were found in cis, and co-segregated in all patients sequenced. Clinical details were available on 22 patients. Five patients had symptoms and signs fulfilling a clinical diagnosis of FMF. Fourteen received colchicine. In patients not reaching the criteria, trials of anti-TNF agents resulted in partial or no benefit; resolution of symptoms was noted in those receiving anakinra. The carrier frequency was higher in the patient cohort than in controls but was not statistically significant. Co-immunoprecipitation studies demonstrated that these pyrin variants did not affect binding to PSTPIP1.
Conclusions: P369S/R408Q substitutions are associated with a highly variable phenotype, and are infrequently associated with typical FMF symptoms, however a trial of colchicine is warranted in all. Functional and modeling studies suggest that these substitutions do not significantly affect pyrin's interaction with PSTPIP1. This study highlights the need for caution in interpreting genetic tests in patients with atypical symptoms.